Contrasting Effects of Oxytocin on MK801-Induced Social and Non-Social Behavior Impairment and Hyperactivity in a Genetic Rat Model of Schizophrenia-Linked Features.

Volumetric brain differences between the Roman rat strains: Neonatal handling effects, sensorimotor gating and working memory

Neurobiology of sensorimotor gating deficits in the Roman rat strains: Studies of c-Fos expression and COMT activity

Dopamine is involved in the different patterns of copulatory behaviour of Roman high and low avoidance rats: Studies with apomorphine and haloperidol

Letter to the Editor

The Roman high- and low-avoidance rats differ in the sensitivity to shock-induced suppression of drinking and to the anxiogenic effect of pentylenetetrazole

Rats of the Roman high-(RHA) and low-avoidance (RLA) lines are known to differ in alcohol preference, since the RHA rats freely consume more ethanol than RLA animals. In order to investigate whether this difference in alcohol intake could be due to an alteration of the gustatory quality of ethanol induced by the selection, we compared taste preference and aversion responses of RHA and RLA rats in four procedures: saccharin-water choice; gustatory negative contrast; quinine-water choice and 10% v/v alcohol-water choice. Our results confirm that RHA rats drink more alcohol than RLA rats. In the saccharin-water choice task, RHA rats tended to show higher preference than RLA rats for the most palatable concentrations, while their aversion to the highest concentration of saccharin (50mM) was smaller than the aversion shown by RLA rats. The negative gustatory contrast test did not clearly differentiate the two lines, although only RHA rats showed significant negative contrast. Lastly, while RLA rats showed only aversion to quinine as the concentration increased, RHA rats did not show any aversion and preferred quinine to water at mid-range concentrations. To explain these results three hypotheses are briefly discussed: first, selective breeding for high avoidance learning could have enhanced brain reinforcement processes implicated in the evaluation of palatability. Secondly, selective breeding could have decreased aversiveness to quinine-adulterated solutions, as well as to saccharin and alcohol solutions which include a quinine-like taste component. Lastly, the present results suggest that the RHA rats may be high sensation-seekers whereas RLA animals are low sensation-seekers.

Roman High- (RHA) and Low-Avoidance (RLA) outbred rats, which differ for a respectively rapid vs. poor acquisition of the active avoidance response in the shuttle-box, display differences in sexual activity when put in the presence of a sexually receptive female rat. Indeed RHA rats show higher levels of sexual motivation and copulatory performance than RLA rats, which persist also after repeated sexual activity. These differences have been correlated to a higher tone of the mesolimbic dopaminergic system of RHA rats vs. RLA rats, revealed by the higher increase of dopamine found in the dialysate obtained from the nucleus accumbens of RHA than RLA rats during sexual activity. This work shows that extracellular dopamine and noradrenaline (NA) also, increase in the dialysate from the medial prefrontal cortex (mPFC) of male RHA and RLA rats put in the presence of an inaccessible female rat and more markedly during direct sexual interaction. Such increases in dopamine (and its main metabolite 3,4-dihydroxyphenylacetic acid, DOPAC) and NA were found in both sexually naïve and experienced animals, but they were higher: (i) in RHA than in RLA rats; and (ii) in sexually experienced RHA and RLA rats than in their naïve counterparts. Finally, the differences in dopamine and NA in the mPFC occurred concomitantly to those in sexual activity, as RHA rats displayed higher levels of sexual motivation and copulatory performance than RLA rats in both the sexually naïve and experienced conditions. These results suggest that a higher dopaminergic tone also occurs in the mPFC, together with an increased noradrenergic tone, which may be involved in the different copulatory patterns found in RHA and RLA rats, as suggested for the mesolimbic dopaminergic system.

Schizophrenia-relevant social, attentional and cognitive traits in female RHA vs. RLA rats: effects of neonatal handling

IntroductionThe selective breeding of Roman High‐ (RHA) and Low‐Avoidance (RLA) rats for, respectively, rapid versus poor acquisition of the active avoidance response has generated two distinct phenotypes differing in many behavioral traits, including coping strategies to aversive conditions. Thus, RLA rats are considered as a genetic model of vulnerability to stress‐induced depression whereas RHA rats are a model of resilience to that trait. Besides the monoamine hypothesis of depression, there is evidence that alterations in neuronal plasticity in the hippocampus and other brain areas are critically involved in the pathophysiology of mood disorders.Materials and MethodsWestern blot (WB) and immunohistochemistry were used to investigate the basal immunochemical occurrence of brain‐derived neurotrophic factor (BDNF) and its high‐affinity tyrosine‐kinase receptor trkB in the dorsal and ventral hippocampus of adult RHA and RLA rats.Results WB analysis indicated that the optical density of BDNF‐ and trkB‐positive bands in the dorsal hippocampus is, respectively, 48% and 25% lower in RLA versus RHA rats. Densitometric analysis of BDNF‐ and trkB‐like immunoreactivity (LI) in brain sections showed that BDNF‐LI is 24% to 34% lower in the different sectors of the Ammon's horn of RLA versus RHA rats, whereas line‐related differences are observed in the dentate gyrus (DG) only in the ventral hippocampus. As for trkB‐LI, significant differences are observed only in the dorsal hippocampus, where density is 23% lower in the DG of RLA versus RHA rats, while no differences across lines occur in the Ammon's horn.ConclusionThese findings support the hypothesis that a reduced BDNF/trkB signaling in the hippocampus of RLA versus RHA rats may contribute to their more pronounced vulnerability to stress‐induced depression.

Prepulse inhibition deficits in inbred and outbred rats and between-strain differences in startle habituation do not depend on startle reactivity levels

Active avoidance learning differentially activates ERK phosphorylation in the primary auditory and visual cortices of Roman high- and low-avoidance rats

Density of acetylcholine esterase (AchE) and tyrosine hydroxylase (TH) containing fibers in the amygdala of roman high- and low-avoidance rats

P.1.h.031 Dopamine is involved in the different copulatory patterns of Roman high and low avoidance rats: studies with apomorphine and haloperidol

The Roman high(RHA) and low-Avoidance (RLA) rats were selectively bred for rapid vs poor acquisition of two-way active avoidance behavior. These lines differ in numerous behavioral traits, with RLA rats being more fearful/anxious than RHA rats, and the latter being novelty-seekers and showing larger intake of, and preference for, addictive substances including ethanol (ETH). Moreover, several differences in central dopaminergic, serotonergic, and GABAergic functions have been reported in these two lines. Since those neural systems are involved in the regulation of ETH consumption, it was considered of interest to investigate: 1) the differences in ETH intake and preference between RHA and RLA rats, 2) the effects of ETH on DA release in the shell of the nucleus accumbens (AcbSh) using brain microdialysis. ETH solutions of increasing concentrations (2% - 10%) were presented on alternate days in a free choice with water. To examine ETH intake and preference stability, animals were subsequently switched to daily presentations of 10% ETH for 10 consecutive days. RHA rats consumed significantly larger amounts of ETH and displayed higher ETH preference than did RLA rats throughout the acquisition and maintenance phases. Following chronic exposure to ETH the animals were habituated to a restricted access to ETH schedule (2% ETH, 2 h per day × 4 days) before surgical implantation of a dialysis probe in the AcbSh. Under these experimental conditions, voluntary ETH intake (2%, 1 h, p.o.) produced a significant increase in accumbal DA output in RHA rats but not in their RLA counterparts. Finally, the i.p. administration of ETH (0.25 g/kg) to na?ve Roman rats produced a significant increment in accumbal DA output only in RHA rats. These results indicate that the mesolimbic dopaminergic system of RHA rats is more responsive to the effects of ETH than that of RLA rats.

Objectives Yokukansan, a traditional Japanese medicine, has been approved by the Ministry of Health, Labour, and Welfare of Japan as a remedy for neurosis, insomnia or night crying and irritability in children. It has recently been reported to improve behavioural and psychological symptoms of dementia, such as hallucinations, agitation, and aggressiveness in patients with some forms of senile dementia. Little is known about the mechanism underlying the effectiveness of yokukansan. Our aim was to clarify the involvement of yokukansan in serotonergic function in para-chloroamphetamine (PCA)-induced aggressive behaviour in rats. Methods The effect of yokukansan on social interactions, including social and aggressive behaviour, was examined in PCA-injected rats. Concentration and release level of serotonin (5-HT) in the hypothalamus were measured. Key findings PCA reduced not only the 5-HT concentration but also the high K+ -induced 5-HT release in the rat hypothalamus. Social interaction tests showed a significant decrease in social behaviour and a significant increase in aggressive behaviour in the PCA-treated rats. The decrease in social behaviour was ameliorated by the 5-HT1A agonist buspirone and further decreased by a 5-HT1A antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclo-hexanecarboxamide trihydrochloride (WAY-100635), whereas it was further decreased by the 5-HT2A agonist, 2,5-dimethoxy-4-iodoamphetamine (DOI), and ameliorated by the 5-HT2A antagonist ketanserin. On the other hand, the increase in aggressive behaviour was ameliorated by buspirone but not affected by WAY-100635, whereas it was enhanced by DOI and ameliorated by ketanserin. A single injection of yokukansan ameliorated the PCA-induced decrease in social behaviour but not aggressive behaviour. Chronic treatment for 14 days with yokukansan ameliorated PCA-induced abnormal behaviour, decreased social behaviour and increased aggressive behaviour, but it did not ameliorate PCA-induced decreases in the cerebral 5-HT concentration and 5-HT release. The ameliorative effects of chronic yokukansan on behaviour were counteracted by co-administration of WAY-100635. Conclusions These results suggest that yokukansan might have two different effects: an acute effect on social behaviour and a chronic effect on aggressive behaviour. One of the mechanisms of these effects of yokukansan may be related to the agonistic effect on 5-HT1A receptors.