key: cord-0009314-d0a1dobq
authors: Andersson, Tommy; Mohammed, Abdul K.H.; Henriksson, Bengt G.; Wickman, Charlotte; Norrby, Erling; Schultzberg, Marianne; Kristensson, Krister
title: Immunohistochemical and behaviour pharmacological analysis of rats inoculated intranasally with vesicular stomatitis virus
date: 2003-03-19
journal: J Chem Neuroanat
DOI: 10.1016/0891-0618(93)90003-m
sha: cca041657183da140d9bff16a7ec097eb67cdc41
doc_id: 9314
cord_uid: d0a1dobq

A temperature-sensitive mutant of vesicular stomatitis virus was inoculated intranasally into infant Sprague Dawley rats aged 9 to 17 days. Rats receiving the virus at 9 days of age had an extensive spread of infection throughout the brain and the animals died after a few days. Rats inoculated at day 11 postnatally survived and the infection was limited to the olfactory pathways, hypothalamus, diagonal bands and the anterior raphe nuclei. Stereological measurements showed that the volume of infected neurons constituted 67 ± 10% of the total neuronal volume in the dorsal raphe nucleus. Double-labelling experiments revealed that both 5-hydroxytryptamine- and substance P-immunoreactive neurons contained the virus antigen. The motor stimulant effect of amphetamine was studied at 3 months post infection. The increase in amphetamine-induced frequency and duration of rearing was significantly attenuated in infected rats and the amphetamine-induced locomotion was slightly reduced.

Certain neurotropic viruses can invade the brain along the olfactory routc after an infection of the olfactory mucosa (for review see Johnson, 1982: Tomlinson and Esiri, 1983; Morales el al., 1988; Barthold. 1988 : Perlman et al., 1989 Shankar el al., 1992) . Neurons in the diagonal bands, locus coeruleus and anterior raphe nuclei, which form part of the reticular core, project directly to the olfactory bulbs and can, via retrograde axonal transport, be labelled by tracers injected into the ollitctory bulb (Shipley and Adamek, 1984) or even instilled into the nasal cavity (Shipley, 1985) . These groups of neurons were also labelled by vesicular stomatitis virus (VSV) antigen following intranasal infection with the virus in mice (Lundh el al., 1987) . B\ using a temperature-sensitive mutant (G41) o1" VSV and the fact that olfactory spread of VSV is age-dependent (Sabin and Olitsky, 1937) a non-lethal infection involving these neurons was obtained in stickling mice (Lundh el al., 1988) . In ordcr to pcrl\~rm corrclativc neurochemical and behavioural studies, infant rats were then infected and we have previously shown that intranasal instillation of the VSV mutant G41 results in a marked depletion of serotonin in the hippocampus and cerebral cortex with no substantial effects oll dopamine, noradrenaline, choline acetyltranst'erase and glutamate decarboxylase (Mohammed ~' 1 ~d., 1990 (Mohammed ~' 1 ~d., , 1991 . Behavioural changes induced by the infection included increased motor activity. Both the serotonergic raphe neurons and the dopaminergic nigro-cortical neurons have been implicated in arousal and motor activation (Fibiger and Campbell, 1971 : Lucot and Seiden, 1986 : Mabry and Campbell, 1974 . As a first step towards studying the behavioural pharmacology of VSVinduced hyperactivity, we examined the effect of amphetamine. This drug has been widely used as a tool to release monoaminergic transmitters from their axon terminals in studies on the ett'ects of monoamines on motor activity (for review sec Moore, 1974) . Here we present a detailed account of the distribution of VSV antigen in the rat brain and report that VSV antigen is present in a ma,iority of the anterior raphe neurons and that amphetamineinduced increase in duration and frequency of rearing was attenuated by VSV infection.

A temperature-sensitive mutant of VSV, designated G41, was used in all experiments. The characteristics of this mutant have been described previously (Rabinowitz et al., 1976) . The VSV strain was generously provided by Dr Mauro Dal Canto, Department of Pathology, Northwestern University, Illinois, USA. The mutants were grown in BHK21 cells and plaque titrated as described earlier (Lundh et al., 1987 (Lundh et al., , 1988 . Ten gl of virus suspension were instilled twice into each nostril of suckling Sprague-Dawley rats (ALAB, Sollentuna, Sweden) (n = 197) using a micropipette, exposing each animal to about 3-6 x 10 6 plaque-forming units of the virus. Controls (n=77) received an equal amount of the virus vehicle (Eagle's Minimal Essential Medium, Flow Laboratories, Scotland). The animals were kept under standard laboratory conditions, employing a 12/12 h light cycle.

In order to determine age-dependency of virus spread through the olfactory system, one to four litters, aged 9, 10, 11, 12, 13, 15 and 17 days, were used (in total 140 infected and 40 uninfected rats). The size of the litters was standardized immediately after birth to ten pups per litter, each consisting of five male and five female pups. The rats were weighed once a day during the whole observation period.

Seventeen rats, inoculated with virus at 11 days of age, were perfused through the heart with 4% paraformaldehyde in S6rensens phosphate buffer (pH 7.2) at days 3, 5, 7, 9 and 11 post inoculation (p.i.). The brains were dissected, postfixed for 90min, subsequently rinsed and kept in 10% sucrose for at least 24 h prior to cutting on a cryostat (Frigocut 2800E, Reichert-Jung, Germany). Four uninfected rats perfused at days 5 and 11 p.i. served as controls. Twelve gm thick sections, from more than 50 different levels of each brain, were stained with cresyl violet and mounted in Entellan (Merck, Germany). Viral antigen was demonstrated in adjacent sections by the peroxidase-antiperoxidase method (Sternberger, 1979 ) employing a sheep anti-VSV hyperimmune serum (kindly provided by Dr Jan Zfivada, Institute of Virology, Slovak Academy of Sciences, Bratislava, Czechoslovakia; for characterization and details of procedure see Lundh et al., 1988) . Sections were also processed for doublelabelling with the sheep anti-VSV hyperimmune serum and antibodies raised in rabbits to 5-hydroxytryptamine (5HT) (Steinbusch, 1981; Steinbusch and Verhofstad, 1979) (generously provided by Dr Harry W. M. Steinbusch, Faculty of Medicine, Department of Pharmacology, Free University of Amsterdam, The Netherlands) or synthetic substance P (Brodin et al., 1986) . Incubation with the primary antisera at 4C overnight was followed by a thorough rinse of the sections in 0.01 M-phosphatebuffered saline (PBS; pH 7.4). The sections were then incubated for 30 min at 37'~C with tetramethylrhodamine isothiocyanate-labelled swine anti-rabbit antibodies (Dakopatts, Copenhagen, Denmark) and after thorough washing in PBS, with fluorescein isothiocyanate-labelled rabbit anti-sheep antibodies for 30 min. Finally, the slides were washed in PBS, mounted in PBS-buffered glycerine with 0.1% pphenylene diamine (Johnson and de C. Nogueira Araujo, 1981) and examined in a Nikon Optiphot fluorescence microscope.

In order to improve visualization of substance P immunoreactivity in nerve cell bodies, three I l-dayold rats were infected and at day 7 p.i. injected stereotactically into the right lateral ventricle with 5 ~1 of colchicine (2 gg/!al; Sigma Chemical Company, St Louis, USA) dissolved in 0.9% saline. Two uninfected control rats were treated in the same way. Twenty-four hours later the rats were perfused and processed for immunohistochemistry using the double-labelling method described above.

Four animals, inoculated at 9 days of age, were perfused at day 5 p.i. and processed for demonstration of viral antigen as described above.

Stereology in order to quantify the extent of virus infection in the raphe nuclei, the proportion of infected neurons in the dorsal raphe nucleus was determined by stereological measurements (see Weibel, 1979) in five infected rats and two controls, sampled at days 5 and 7 p.i. Firstly, the volume density (I,/",) of the neurons in the dorsal raphe nucleus, i.e. their relative volume as compared to the total volume of the nucleus, was calculated in sections from six random levels of the dorsal raphe nucleus of each animal (infected and uninfected). This was done in order to evaluate if there was any cell loss in the raphe nuclei of the infected rats. Secondly, the volume density of the infected neurons, i.e. their relative volume as compared to the total volume of neurons, was determined. In addition, the absolute volume of the dorsal raphe nucleus was calculated. The volume of the infected neurons was calculated from micrographs of sections immunohistochemically labelled for virus antigen, whereas the total volume of nerve cells and the volume of the whole dorsal raphe nuclei was evaluated on adjacent cresyl violet-stained sections using a Reichert-Jung Visopan microscope.

Rats inoculated at 11 days of age were used for motor activity tests. This group consisted of 64 animals (26 males and 38 females), about half of which were infected. Motor activity was tested 3 months p.i., separately for males and females, using automated activity cages (Mohammed et al., 1990) tests x~ere perl\irmed between 9 a.m. and 2 p.m. Thcse cages were equipped with two rows of photocells which registered both locomotion (horizontal activity) and rearing (vertical activity). Four activity cages were used at the same time. The animals were placed in the cages and the activity was registered cver> 10rain during I h. After a l-h habituation period, half of the animals received a subcutaneous injection of Img:kg d-amphetamine sulphate (Apotcksbolaget, Stockholm, Sweden), while the othcr half received a subcutaneous injection of saline. The rats were then placed in the activity cages, and the motor activity was registered every If)rain for a period of 90rnin. The resulting data were analysed by a two-way analysis of variance t ANOVA), and the Tukey test was used lk)r post hoc conlpa risons.

All rats inoculated with virus at 9 days of age underwent a significant weight loss as compared to uninfected controls, and died within 1 week p.i. Rats inoculated at 10 days of age showed a mortality of 68~!. (l:ig. 1 ), while those aged 11 days or more at the timc of inoculation displayed a mortality rate not significantly higher than that of controls. The rats infected at 1 I days of age did not exhibit any significant loss of body weight, with the exception of five rats (out of the 40 infected rats used in the agedepcndency studies), which suffered from a severe x~eight loss of about 30 40% before death. At the time of the behavioural test, the mean weights of the female rats were 280:k5 g. and 27"7+5 g for VSV-infected and uninfected, respcctixety. Thc corresponding figures for the males \~crc 450 +_ 1 I g and 450= 10 g.

The studies of virus spread and motor activity were perl\~rmed on the rats which showed no signiticant lossofbody weight when infected at day 11 postnatallv. Virus antigen was detected at day 3 p.i. m neurons in the anterior ollhctory nucleus, the anterior part of the olfactory cortex, the horizontal and vertical limbs of the diagonal band, and scattered in the hypothalamus (anterior, dorsal, lateral and paraventricular). In the diagonal bands, an average of 55 70"i. of the neurons were immunereactive for virus antigen. Thc horizontal band appeared to be somewhat more all'ecled than the vertical band. Thc spread of virus at 5 days p.i. is depicted in Fig. 2 . A largc nuinbcr of xirus-positi~e neurons could then be seen in the central, median and dorsal raphe nuclei (Fig. 3A ) . No xirus antigen could be seen in the nucleus raphe magnus, obscurus and pallidus. In the locus coeruleus only a few neurons, not exceeding 5%, were labelled. Virus antigcn could not be detected in other nuclei of the brainstem, nor in the basal ganglia, the substantia nigra, the ventral tegmental area, thc hippocampus or the neocortex. Rats examined at day 7p.i. showed immunoreactivity for virus antigen in the brain, with a similar distribution pattern as seen at day 5 p.i. The amount of virus antigen ,aas markedly redticed 9 days p.i., due to the c,vtocidal effects of this virus (Wagner, 1990) . After II days. only a few cells containing antigen could be seen in these a r e~.l s.

Three of the live rats infected at day 11 post-natall\, and displaying a severe weight loss, were examined and showed an cxtensive spread of virus in the brain. Thus, many clusters of infected ncurons could be seen in cortical as well as in subcortical areas throughout the brain, including hippocampus and neocortex, and in the cerebellum. A similar spread of virus throughout the central nervous system was observed in four rats inoculated at 9 days of age which had survixed until dav 5 p.i. These rats also suffered from a severe weight loss.

The volume of the entire dorsal raphe nucleus was about 1.8 4-0.1 × 10 <j btm 3 (mean + SEM), and there was no signifcant difference between infected and control rats. The 1" of inlbcted neurons (at days 5 and 7 p.i.) as compared to the total vohnne of neurons in the dorsal raphe nucleus was 0.67 _+ 0.10 (mean +_SEM), thus representing 67% of the total cell volume. There was no significant difference between infected and control animals in lhc 1' of Fig. 2 . Spread of VSV antigen in the rat brain 5 days after nasal inoculation of 1 l-day-old animals. The distribution of virus antigen was studied by immunohistochemistry and depicted (stars) in schematic drawings of six horizontal levels of the brain. Note the abundance of virus in the olfactory nucleus, diagonal bands and the anterior raphe nuclei. the total number of neurons in the dorsal raphe nucleus, indicating that there was no major cell loss in the infected rats at days 5 and 7 p.i.

The majority of the neurons in the raphe nuclei were 5HT-positive (Fig. 3B ). The substance Pimmunoreactive cells could be seen after colchicine treatment, and were scattered in the raphe nuclei. Double-labelling (5HT/virus antigen, substance P/virus antigen) revealed the occurrence of virus antigen in most 5HT- (Fig. 3A, B) and substance P-immunoreactive neurons, respectively, in the raphe nuclei. A small proportion of the viruspositive neurons were 5HT-negative and some 5HT-immunoreactive neurons were virus-negative in double-stained sections, indicating that the observation of staining for virus proteins in 5HT-immunoreactive neurons was not due to 'fluorescence bleeding'.

Locomotion counts are shown in Fig. 4A . Two-way ANOVA revealed a significant main effect of group (P < 0.0001), and a significant group × period interaction (P = 0.0003). Tukey test showed that the VSV-infected saline-injected animals had slightly higher locomotor scores than the uninfected saline-injected animals, but no significant differences between these two groups were obtained. Nor did the amphetamine-treated groups differ significantly from each other. The two groups given amphetamine (infected and uninfected) had significantly higher locomotor scores than the groups that received saline, and the locomotor scores of the uninfected amphetamine-treated group were significantly higher than those of the uninfected saline-injected group at all the 10-min time periods, whereas the locomotor scores of the VSV-infected amphetamine-treated group differed significantly from the VSV-infected saline-injected group only at the 50-, 60-and 70-min periods.

Females. Fig. 4B shows the results on locomotion counts for the female rats. Two-way ANOVA showed a significant group effect (P<0.0001) and a significant group x period interaction effect (P<0.0001). Tukey test showed that there was no difference in locomotor scores between uninfected and infected female rats. Similar to the male rats, the locomotor scores of the amphetamine-treated groups (infected and uninfected) were significantly different from the saline-injected groups (infected and uninfected) at all time periods.

,'~lah's." Results from the rearing frequency counts are shown in Fig. 5A . Two-way ANOVA indicated a significant group effect (P<0.05). Subsequent Tukey test showed that for uninfected rats, amphetamine-treated animals had signiticantly higher rearing scores than the saline-injected rats. In infected rats, there was no significant increase in rearing caused by amphetamine treatment.

There was a significant interaction effect also on rearing duration (Fig. 5B: P<0 .05). Post hoc test showed that for the uninfected groups, amphetamine-treated animals had a significantly longer duration of rearing at 60.70 and 80 rain. After VSV infection, the amphetamine-treated animals did not differ significantly from the saline-treated ones.

Females. Fig. 6A shows the results on rearing frequency. Two-way ANOVA revealed a significant group effect (P<0.0001) and a significant group x period interaction effect (P<0.0001). Tukey test showed that the VSV-infected amphetamine-treated rats had significantly lower rearing scores than the uninfected amphetamine-treated rats at the 50-, 60-, 70-, S0-and 90-min periods. Similar to the male rats, there was a significant increase in rearing scores after amphetamine treatment in the female uninfected rats (P<0.01), and there was a smaller but significant increase in rearing scores in the infected rats (P < 0.05). There was in fact a significant difference in rearing scores alter amphetamine treatment between infected and uninfected female rats.

The results of rearing duration are shown in Fig.  6B . A significant group (P < 0.0001) and interaction (P<0.0001) effect was seen. Post hoc test showed significant effects on rearing duration similar to those for rearing frequency.

The spread of VSV in infant rats was remarkably age-dependent, as shown in the early study by Sabin and Olitsky (1937) and in our previous study on mice (Lundh el al., 1988) . The susceptibility decreased dramatically between 9 and I 1 days postnatally. While the 9-day-old rats died soon after infection with an extensive spread of infection throughout the brain, the 11-day-old rats survived with an infection limited to the olfactory pathways. hypothalamus, diagonal bands and the anterior raphe nuclei. The reason for this age-dependent restriction of virus spread in the brain is unclear, but may involve factors from the host animal's immune or defence system. The maturity of the nervous system pep" .s'e may also be of importance for the viral growth (Dubois-Dalcq el al., 1982 : Grifl:in el al., 1974 . During the second week of life, the anterior raphe nuclei (and the diagonal bands) are characterized by marked alterations in axonal and dendritic arborization, remodelling of cortical innerw~tion and changes in transmitter receptivity including second messengers (D'Amato el al., 1987: Jonsson and Kasamatsu, 1983; Lidow and Molliver, 1982: Zifa elal., 1988) .

The rats infected at day 11 postnatally had an extensive infection in the anterior raphe nuclei, i.e. the volume of infected neurons constituted 67%, of the total neuronal volume in the dorsal raphe nucleus. Double-labelling experiments revealed that most of the 5HT-immunoreactive neurons and thc substance P-immunoreactive neurons, respectively, were infected. Also in tracer studies on connectivity between the olfactory bulbs and the anterior raphe nuclei, it was found that a majority of the raphe neurons project to the ollhctory bulbs <de OImos el al., 1978: Macrides et al., 19S1: Shipley and Adamek, 1984: Shipley, 1985) .

The neuroanatomically restricted VSV refection also had functional consequences. Thus, we recently found that VSV infection leading to lesion of the raphe system in rats caused persistent learning deficits in the Morris maze and impaired exploratory behaviour in the open field test (Mohammed et al.. 1990 (Mohammed et al.. , 1991 . In the present study, we subjected the rats to the psychomotor stimulant amphetamine. The motor stimulatory action of amphetaminc is mediated by diverse transmitter systems such as dopaminergic (Creese and lversen, 1975 : Kelly el al., 1975 : Shaywitz t,t a/., 1976 , noradrenergic (Mohammed el al.. 1986 ) and cholinergic (Robinson, 1986) neurons. Of interest to the present work are a number of studies demonstrating that the central action of amphetamine can be modified by manipulation also of the serotonergic system. The weight of evidence indicates that the locomotor stimulant effect of at-nphetamine is attenuated b 3 increased serotonergic transmission (Warbritton t't al., 1978; Carter and Pycock, 1978) and enhanced by blockade or destruction of the serotonin system The results demonstrate counts at 10-min intervals (left panel, presented as mean; SEM left out for the sake of clarity) as well as the cumulative counts for the entire 90-min test period (right panel, presented as mean-t-SEM). VSV-infected rats were more active than uninfected controls during the 60-min pre-injection habituation period. *P < 0.05, **P< 0.01. Statistical significance with respect to C + Sal and V+Sal. (Breese et al., 1974; Mabry and Campbell, 1974; Neill et al., 1972) .

In the present study, amphetamine treatment increased locomotion to some extent in uninfected and VSV-infected rats. However, with regard to rearing, there was a marked reduction of the amphetamine-induced increase in rearing scores observed in the VSV-infected animals. This was the case both for the frequency and the duration of rearing. Little is known about the neuronal basis of rearing. Rearing can be considered as a measure of exploratory behaviour (Archer, 1973) , which includes cognitive function and locomotion. Amphetamine increases rearing in a dosedependent manner locomotion (Sandberg cl a/.. 1987) . Most studies have considercd the locomotor component of amphetamine-induced activity and, as mentioned abo'~e, it appears that this aspect of motor behavtour is mainly tinder tile control of dopaminergic and serotonergic mechanisms. Our findings suggest that serotonergic neurons are critically involved in mediating aiTlphetamine-induced rearing. Since substance P-containing neurons, which are revolved in cognitive function (Huston and Oitzl, 1989; Hascn~:,hrl el al., 1990L were also infected, this subpopulatiori of neurons may have contributed to this efl'ect. As demonstrated earlier, the stimulant efl'ects of amphetamine ell both locomotion and rearing wcrc more prononnced in female than in rnale rats.

which may be due to sex dilt'erences in brain concentrations of amphetamine after systemic in iections (Becker el al., 1982: West and Michael. 19~4~4) .

The present study showed that virus antigen was present not only in the raphc nuclei, but also in neurons in the olfactory cortex, and the diagonal bands, and in a few noradrenergic iletirtHlS iri the locus coeruleus. However. our previous bioctlemical study showed no consistent reduction in leveb, of choline acetyltransferase and rioradrenalinc.

suggesting ttlat the viral eft'cots on these neurons has been compensated lk)t by tile uninfected ones. Virus antigen was also observed in neurons in diflerent parts of the hypothalamus, which has been shown to be involved in amphetamine-induced locomotor The results demonstrate counts at 10-rain intervals (left panel, presented as mean; SEM left out for the sake of clarity) as well as cumulative counts for the entire 90-min test period (right panel, presented as mean ___ SEM. VSV-infected rats were more active than controls during the 60-rain pre-injection habituation period. *P < 0.05, **P < 0.01. Statistical significance with respect to C + Sal and V+Sal. +P<0.05. Statistical significance in comparison between C+Amph and V+Amph. stimulation in rats (Shian et al., 1985) . The nigrocortical and nigro-striatal dopaminergic neurons, which are known to control motor activity (Carlsson and Carlsson, 1990) were, however, not infected. We suggest therefore that the attenuation of amphetamine-induced rearing in VSV-infected rats is mainly due to the lesion of the raphe nuclei. Viruses can display a remarkable selectivity in their attack on nervous tissue (Johnson, 1980) , due to differences in routes of infection, in viral cell surface receptors and in host cell restrictions on virus multiplication. Although cellular recognition sites for VSV are considered to be a component of virtually all cells (Emerson, 1985) , this virus infects the neuroepithelia (olfactory mucosa and vomeronasal organ) and not the respiratory epithelium in the nasal cavity (Lundh et al., 1987) . In the brain, VSV infects the anterior optic nucleus and reticular core neurons projecting to the olfactory bulbs. In the present study, the majority of neurons in the diagonal bands and anterior raphe nuclei were attacked, and in the raphe nuclei both substance P and 5HT neurons were infected. Although the locus coeruleus was heavily infected in mice (Lundh et al., 1988) , this nucleus showed only minimal infection in the rat. Recently, a marked retrograde labelling of the diagonal bands, the anterior raphe nuclei and locus coeruleus was found after intranasal infection of herpes simplex virus type I in rats (McLean et al., 1989) , while a mutant strain of rabies virus (AvOl) showed no infection of the raphe nuclei after intranasal instillation, although the wild type did (LaFay et al., 1991 ) . The latter study illustrates that a selectivity in virus attack on groups of neurons projecting within the olfactory system can be obtained. Neither the wild type nor the mutant rabies virus infected the granular cells in the main olfactor3 bulb or the locus coeruleus, and the mutant, although it failed to infect the anterior olfactory nucleus (which the wild type did), gave rise to an extensive infection of the horizontal diagonal band. These studies indicate that there may be selectivity in the attack on the reticular core neurons projecting to the olfactory bulbs by different viruses spreading from the nasal cavity. Viruses and their mutants may, therefore, have potential as valuable tools in combined neurochemical and behaviour studies aimed at evaluating the neuroanatomical correlates of behaviour.

Tests for emotionality in rats and mice: 'a review

Olfactory neural pathway in mouse hepatitis virus nasoencephalities. Acta Neuropathol

Sex differences and estrous cycle variations in amphetamine-elicited rotational behaviour

Evidence l	r involvement of 5-dydroxytryptaminc in the actions of amphetamine

Tachykinin multiplicity in rat central nervous system as studied using antisera raised against substance P and neurokinin A

Interactions bctwecn glutamatcrgic and monoaminergic systems within the basal ganglia implications for schizophrenia and Parkinson's disease

Differential effects of central serotonin manipulation on hyperactive and stereotyped bchaviour

The pharmacological and anatomical substrates of the amphetamine responsc in the rat

Ontogeny of the scrotoncrgic projection to rat neocortex: Transient expression ofa dense mnervation to primary sensory areas

The afferent connections of the main and the accessory olfactory bulb formations in the rat: an experimental tlRP study

Acute and persistent viral infections of differentiated nerve cells

Rhabdoviruses. In liroh

A. 11971 I. The effect of parachlorophenylalanine on spontaneous locomotor activity in the rat

Age dependence of viral expression: comparative pathogenesis of two rodent-adapted stratus of measles virus in mice

Neuropeptide substance P improves water nlazc performance in aged rats. Puctlo/~harn;~zc

The relationship between reinl\)rccment and memory: parallels in the rewarding and nmemonic effects of the neuropeptide substance

A simple method of reducing the fading of immunofluorescence during microscopy

e vulnerability of neural cells to viral infections

Viral h!lbcti(m.s ,l the :V(,rvous Sl'slem

Maturation of nlonoamine neurotransmitters and receptors ill cat occipital cortex during postnatal critical period. Kvp

Amphetamine and apomorphine responscs in the ral lk~llowing 6-OHDA lesion of the nucleus accumbens septi and corpus striatum

Spread of the ('MS strain of rabies virus and of the a

Ig82k llnntunohistochemical study of the development of serotonergic neurons in the rat CNS

Effects of serotonergic agonists and antagonists on locomotor activflv of neonatal rats

Selective infections of olfactory epithelium b~ vesicular stomatitis and Sendal

Non-lethal infection of aminergic reticular core neurons: age-dependent spread of ts ntutant vesicular stomatitis virus from the nose. ,I. NuurW~athoL Evp

Ontogeny of serotonergic inhibition of behavioural arousal in the rat

Cholinergic and catecholaminergic afl'erents to the olfactory bulb in the hamster: a neuroanatomical, biochemical and histochemical investigation

Golgi-like. transneuronal retrograde labelling with CNS injections of herpes simplex virus type 1

Central noradrenaline depletion attenuates amphetamine-induced locomotor behaviour

Behavioural deficits and serotonin depletion in adult rats after transient infant nasal viral infection

Persistent changes in behaviour and brain serotonin during ageing in rats subjected to infant nasal virus infection

Amphetamines: biochemical and behavioural actions in animals

Axonal transport of Borna disease virus along olfactory pathways in spontaneously and experimentally infected rats

Selective potentiation of locomotor effects of amphetamine by midbrain raphe lesions

Spread of a neurotropic murine coronavirus into the CNS via the trigeminal and olfactory nerves

Comparison of central nervous system disease produced by wild-type and temperature-sensitive mutants of vesicular stomatitis virus

6-Hydroxydopamine lesion of the ventral noradrenergic bundle blocks the effect of amphetamine on hippocampal acetylcholine

Amphetamine-induced on-and off-wall rearing in adult laboratory rats

Influence of host factors on neuroinvasiveness of vesicular stomatitis virus. I. Effect of age on the invasion of the brain by virus instilled in the nose

The topography of amphetamine and scopolamine-induced hyperactivity: toward an activity print

Kinelics of virus spread and changes in levels of several cytolytic mRNAs in the brain after intranasal infection of rats with Borna disease virus

Paradoxical response to amphetamine in developing rats treated with 6-hydroxydopamine

Hypothalamic involvement in the locomotor stimulant or satiety action of thyrotropin-releasing hormone and amphetamine

Transport of molecules from nose to brain: Transneuronal anterograde and retrograde labeling in the rat olfactory system by wbeat germ agglutinin-horseradish peroxidase applied to the nasal epithelium

The connections of the mouse olfactory bulb: a study using orthograde and retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase

Distribution of serotoninimmunoreactivity in the central nervous system of the rat. Cell bodies and terminals

lmmunocytochemistrv, 2nd Edn

Herpes simplex encephalitis, lmmunohistological demonstration of spread of virus via olfactory pathways in mice

Rhabdoviridae and their replication

Decreased locomotor activity and attenuation of amphetamine hyperactivity with intraventricular infusion of serotonin in the rat

Practical Methods jbr Biological Morphometry

Mild stress influences sex differences in exploratory and amphetamineenhanced activity in rats

Postnatal development of 5-HT t receptors: [3H]5-HT binding sites and 5HT induced adenylate cyclase activation in rat brain cortex

This work was supported by thc Swedish Medical Rescarch ('ouncil (grant no 04480), Greta and Johan Kocks Foundation and Magl'ms Bergvalls Foundation. The authors wish to thank Associate Professor Finn P. Reinholt for valuable advice conccrnmg the stereological examinations and Dr Allan E. Johnson for statistical aid and help in preparing the figures. The generous gift of anhscrum to substance P by Dr Ernst Brodin, Dept. of Pharmacology, Karolinska lnstilutet, Stockholm, is gratefully acknox~ lodged.