Two-way avoidance and acute shock stress induced alterations of regional noradrenergic, dopaminergic and serotonergic activity in Roman high- and low-avoidance rats

The effects of stress on avoidance in rodents: An unresolved matter

In the face of a possible threat, a range of physiological (e.g., increased heart rate) and behavioral (e.g., avoidance or escape) responses are recruited. Here, we will focus on avoidance, in its persistent form one of the core symptoms of anxiety disorders and obsessive-compulsive disorder. The initial goal of fear and avoidance responses is to increase survival, but if they become persistent or overgeneralize, they can disrupt normal daily functioning, and ultimately even result in anxiety-related disorders. Relatedly, acute stress responses promote adaptation and survival, while chronic stress has been found to aggravate pathophysiology. Thus, stress might trigger the transition from adaptive to maladaptive responses, e.g., from goal-directed to persistent avoidance. Animal models are prime tools to unravel if and how stress influences avoidance. This is typically done by performing stress inductions prior to the assessment of (passive or active) avoidance behavior. Despite its clinical relevance, the current literature on this topic is fragmented, and an overall conclusion is lacking. In this Review, we first recapitulate the state of the art regarding stress and active as well as passive avoidance procedures. We then summarize the behavioral effects of acute and chronic stress on active and passive avoidance, and discuss the main neurobiological findings of the field. Finally, we highlight possible reasons for the largely contradictory findings in the literature and we propose strategies to further unravel the effect of stress on avoidance behavior. A deeper understanding of this currently unresolved matter may provide further insights in the etiology and treatment of anxiety-related disorders.

Rats selectively bred for showing divergent behavioral traits in response to stress or novelty or spontaneous yawning with a divergent frequency show similar changes in sexual behavior: the role of dopamine

Sexual behavior plays a fundamental role for reproduction in mammals and other animal species. It is characterized by an anticipatory and a consummatory phase, and several copulatory parameters have been identified in each phase, mainly in rats. Sexual behavior varies significantly across rats even when they are of the same strain and reared under identical conditions. This review shows that rats of the same strain selectively bred for showing a divergent behavioral trait when exposed to stress or novelty (i.e. Roman high and low avoidance rats, bred for their different avoidance response to the shuttle box, and high and low novelty exploration responders rats, bred for their different exploratory response to a novel environment) or a spontaneous behavior with divergent frequency (i.e. low and high yawning frequency rats, bred for their divergent yawning frequency) show similar differences in sexual behavior, mainly in copulatory pattern, but also in sexual motivation. As shown by behavioral pharmacology and intracerebral microdialysis experiments carried out mainly in Roman rats, these sexual differences may be due to a more robust dopaminergic tone present in the mesocorticolimbic dopaminergic system of one of the two sub-lines (e.g. high avoidance, high novelty exploration, and low yawning rat sub-lines). Thus, differences in genotype and/or in prenatal/postnatal environment lead not only to individual differences in temperament and environmental/emotional reactivity but also in sexual behavior. Because of the highly conserved mechanisms controlling reproduction in mammals, this may occur not only in rats but also in humans.

Pharmacological treatment of hyperinsulineamia in rats depends on coping style

Passive and proactive coping styles are associated with marked differences in behavioral and neuroendocrine responses. Previous studies revealed that the passive individuals are more prone to hyperinsulinemia. Likewise, we hypothesize that different coping styles may require different drugs to treat this. We tested this by treating passive and proactive rats (Roman Low Avoidance and Roman High Avoidance rats respectively) with either Rosiglitazone or with RU486. After eight days of treatment we performed and intravenous glucose tolerance test (IVGTT) and we compared the insulin and glucose levels with those measured during the IVGTT at baseline. Rosiglitazone improved insulin levels during an IVGTT in both passive and proactive coping styles. RU486, however, lowered insulin levels only in rats with a passive coping style. This study suggests that insight in the neuroendocrine differences between passive and proactive coping styles may provide an extra impulse to improve treatment of insulin resistance, since it allows the application of drugs targeted at the individual.

Coping style predicts the (in)sensitivity for developing hyperinsulinemia on a high fat diet in rats

The aim of this study was to explore interactions between coping style and diet as risk factors for developing insulin resistance in rats. We hypothesized that rats characterized by a passive coping strategy are more susceptible for developing insulin resistance and visceral obesity than proactively coping rats, particularly on a high (45%) fat diet. This hypothesis was tested by comparing 1) insulin and glucose responses to an intravenous glucose tolerance test (IVGTT), and 2) body fat distribution, in two rat models for passive and proactive coping styles. We found that the most extremely passive rats are characterized by elevated insulin levels during a IVGTT, even on chow. Moderately passive rats display normal insulin responses under chow conditions, but develop insulin resistance on a high fat diet. Proactive rats are remarkably resistant to insulin resistance and visceral obesity, even when overfeeding on a high fat diet. Carcass analysis revealed that passive rats are characterized by increased epididymal fat deposition, which is in line with the observed differences in insulin resistance. We conclude that a passive personality is prone to develop insulin resistance and visceral obesity on a palatable fat diet and a proactive personality might be protected against the development of diet-induced insulin resistance.

Serotonin and the neuroendocrine regulation of the hypothalamic--pituitary-adrenal axis in health and disease

Serotonin (5-hydroxytryptamine, 5-HT)-containing neurons in the midbrain directly innervate corticotropin-releasing hormone (CRH)-containing cells located in paraventricular nucleus of the hypothalamus. Serotonergic inputs into the paraventricular nucleus mediate the release of CRH, leading to the release of adrenocorticotropin, which triggers glucocorticoid secretion from the adrenal cortex. 5-HT1A and 5-HT2A receptors are the main receptors mediating the serotonergic stimulation of the hypothalamic-pituitary-adrenal axis. In turn, both CRH and glucocorticoids have multiple and complex effects on the serotonergic neurons. Therefore, these two systems are interwoven and communicate closely. The intimate relationship between serotonin and the hypothalamic-pituitary-adrenal axis is of great importance in normal physiology such as circadian rhythm and stress, as well as pathophysiological disorders such as depression, anxiety, eating disorders, and chronic fatigue.

Differential neurochemical properties of central serotonergic transmission in Roman high- and low-avoidance rats

The selective breeding of Roman high- (RHA/Verh) and low-avoidance (RLA/Verh) rats for rapid versus poor acquisition of active avoidant behaviour has produced two behavioural phenotypes with different performances in a variety of animal models of anxiety, in which RLA/Verh rats are consistently more fearful than RHA/Verh rats. In addition, these two lines display different functional properties of brain neurotransmitters like serotonin (5-HT), known to be involved in the expression of anxiety- and depression-related behaviours. Therefore, we used brain microdialysis and [3H]-citalopram binding autoradiography to characterize further the neurochemical properties of 5-HTergic transmission in the two lines. No significant line-related differences were detected in the basal 5-HT output in the frontoparietal cortex (FPCx). In contrast, the increase in the cortical 5-HT output elicited by the systemic administration or the local application, via reverse dialysis, of chlorimipramine and fluoxetine was more robust in RHA/Verh than in RLA/Verh rats. Moreover, the binding signal of [3H]-citalopram to 5-HT re-uptake sites was more intense in the FPCx of RHA/Verh rats than in their RLA/Verh counterparts. These findings suggest that the functional tone of the 5-HTergic projection to the FPCx is stronger in the RHA/Verh line relative to the RLA/Verh line. It is proposed that RLA/Verh rats may be used as a model with heuristic value for studying the role of 5-HTergic transmission in anxiety and in the anxiolytic effects of monoamine re-uptake inhibitors.

Divergent stress responses and coping styles in psychogenetically selected Roman high-(RHA) and low-(RLA) avoidance rats: behavioural, neuroendocrine and developmental aspects

The Swiss sublines of Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats have been genetically selected for good vs. poor performance in two-way active avoidance since 1972. RLA/Verh rats show increased stress responses (e.g. freezing behaviour, ACTH, corticosterone and prolactin secretion) and adopt a more passive (or reactive) coping style when confronted with a novel environment. In the open field, elevated plus-maze, black/white box test, and in a new light/dark open field test, RLA/Verh rats appear to be more anxious than their RHA/Verh counterparts. Anxiety may result from their particular psychophysiological profile, i.e. increased emotionality combined with a passive coping style. In contrast, RHA/Verh rats are less responsive to stress, they show little anxiety in novel situations and tend to be impulsive and novelty (sensation) seekers. Some behavioural differences are already noticeable shortly after birth, but the full pattern appears to stabilize only after puberty. Gene-environment interactions are critical in establishing this pattern. The data reviewed indicate that the differences between RHA/Verh and RLA/Verh rats probably result from a complex interaction among divergent anxiety/emotionality characteristics, differences in locomotor activity and novelty/reward seeking, as well as active vs. passive coping styles. It is proposed further that these divergent personality types are to be found not only in other selective breeding programs but in the form of individual differences in most populations of rats used for this type of research.

Early social deprivation alters monoaminergic afferents in the orbital prefrontal cortex of Octodon degus

The influence of early parental deprivation on the development of tyrosine hydroxylase- and 5-hydroxytryptamine-immunoreactive fiber innervation of subregions of the orbital prefrontal cortex (ventrolateral orbital, lateral orbital and agranular insular cortex) was quantitatively investigated in the precocious lagomorph Octodon degus. Forty-five-day-old degus from two groups were compared: 1) degus which were repeatedly separated from their parents during the first three postnatal weeks, and after weaning they were reared in social isolation; and 2) degus which were reared undisturbed in their families. Compared with the normal control animals the ventrolateral orbital prefrontal cortex and agranular insular cortex of the deprived animals displayed significantly increased density of tyrosine hydroxylase-immunoreactive fibers (up to 172% in the ventrolateral orbital prefrontal cortex and up to 143% in the agranular insular cortex). The lateral orbital prefrontal cortex showed increased 5-hydroxytryptamine-positive fiber densities (up to 118%). This altered balance between the serotonergic and dopaminergic cortical innervation in the orbital prefrontal cortex may reflect an anatomical and functional adaptation, which may be triggered by an altered activity of these transmitter systems during the phases of parental separation and social isolation.

Individual response profiles of male Wistar rats in animal models for anxiety and depression

Previous work has shown that systematic individual differences between male Wistar rats can be detected in tasks like the elevated plus-maze, or the open field. Here, we investigated whether individual profiles of anxiety, as measured with the plus-maze, may predict behavioral response profiles in other tasks where anxiety, aversion, or depressive behaviors are important. Male Wistar rats were initially screened: (A) in an open field; and (B) in an elevated plus-maze. Based on their plus-maze behavior, that is, the time spent in the open arms, the animals were divided into two subgroups with either 'low' or 'high' anxiety (LA or HA) levels. These subgroups were exposed to other experimental anxiety paradigms, namely object burying and two-way active avoidance, and an animal model of depression, the forced swim test. In the plus-maze, the percentage of time spent on, and the number of entries into the open arms were lower in HA than in LA rats. In the object burying task, HA rats showed more burying behavior of Tabasco-coated marbles, and in the active avoidance task, they showed slower acquisition of avoidance learning and higher escape latency as compared to LA rats. Finally, LA and HA rats behaved similarly in the forced swim test; however, the percentage changes of immobility time between test days 1 and 2 were negatively correlated to open field behavior, namely locomotor activity and center entries. On the other hand, the frequencies of rearing in the open field, which can also gauge functional differences between rats (for example responsiveness to novelty, psychomotor activation), were not substantially related to the behavioral profiles in the tests of anxiety and depression. These results show that individual differences of anxiety in the plus-maze can be predictive of behavior in other anxiety models, but not in forced swim test, indicating that they may be determined partly by similar functional and physiological mechanisms.

Maternal separation followed by early social deprivation affects the development of monoaminergic fiber systems in the medial prefrontal cortex of Octodon degus

The influence of early postnatal socio-emotional deprivation on the development of tyrosine hydroxylase- and 5-hydroxytryptamine-immunoreactive fiber innervation in the medial prefrontal cortex was quantitatively investigated in the precocial rodent Octodon degus. Forty-five-days-old degus from two groups were compared: (i) degus which were repeatedly separated from their mothers during the first three postnatal weeks and after weaning reared in complete isolation; and (ii) degus which were reared under normal undisturbed social conditions. The two monoaminergic fiber systems in the four subregions of the medial prefrontal cortex responded differentially to the deprivation. While the infralimbic cortex was the only subregion that displayed an increase in 5-hydroxytryptamine-positive fiber densities (129.2%) but no changes in tyrosine hydroxylase-immunoreactive fibers, the precentral medial (82.2%), anterior cingulate (74.6%) and prelimbic cortex (86.9%) showed significantly reduced tyrosine hydroxylase-positive fiber innervation, but no changes in 5-hydroxytryptamine-immunoreactive fiber densities. The number of tyrosine hydroxylase-positive somata in the ventral tegmental area and in the substantia nigra remained unchanged. In cortical areas the number of tyrosine hydroxylase-immunoreactive somata was increased (depending on the medial prefrontal cortex subregion between 241.8% and 398.7%) in deprived animals. This altered balance between the serotonergic and dopaminergic cortical innervation in the different subregions of the medial prefrontal cortex may reflect a counter-regulative anatomical and functional adaptation, which may be triggered by an altered activity of these transmitter systems during the phases of maternal separation and social isolation.

Psychogenetically selected (Roman high- and low-avoidance) rats differ in 24-hour sleep organization

A comparison of sleep organization in Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats, which differ in the way they respond to environmental stimuli and in several neuroendocrine and neurochemical parameters, was carried out. EEG-sleep recordings were obtained from adult males over 12:12 light-dark periods to determine how these two psychogenetically selected rat lines might also differ in their sleep-wake cycle. There was no significant difference in total sleep time between the two lines. However, the (hypoemotional) RHA/Verh rats showed an overall increase (percentage of total sleep) in paradoxical sleep (PS) duration, with a concomitant decrease in slow-wave sleep (SWS). During the dark phase, RHA/Verh rats showed a shorter PS latency and a larger number of PS episodes. Hourly sleep scoring also revealed a more discontinuous pattern (total sleep and PS vs. SWS) during the dark phase in RHA/Verh rats. In relation to recognized neurochemical and neuroendocrine differences between them, these rat lines may prove useful in investigations of the neurobiological mechanisms underlying sleep regulation.

Pharmacological properties of the GABA(A) receptor complex from brain regions of (hypoemotional) Roman high- and (hyperemotional) low-avoidance rats

The pharmacological properties of benzodiazepine binding sites of the gamma-aminobutyric acid (GABA)A receptor complex from cortical, hippocampal and cerebellar membranes of Roman high-avoidance (RHA/Verh) and Roman low-avoidance (RLH/Verh) rats were investigated. No major differences between the two lines were found in the binding parameters of [3H]flunitrazepam (a non-selective agonist). [3 H]zolpidem (a Type I selective agonist) or [3 H]ethyl 8-azido-6-dihydro-5-methyl-6-oxo-4H-imidazol[1,5-a]-[1,4]benzodiazepine- 3-carboxylate (Ro15-4513) (a partial inverse agonist). Neither the Kd values nor the Bmax for these ligands differed between RHA/Verh and RLA/Verh rats in any of the brain regions studied. As a result, the proportion of Type I binding sites in cortical and hippocampal membranes of RHA/Verh and RLA/Verh rats or the 'diazepam-sensitive' and the 'diazepam-insensitive' binding sites in cerebellar membranes, calculated from the [3H]flunitrazepam and [3H]zolpidem maximal binding sites or from [3H]Ro15-4513 binding (in the absence or in presence of diazepam), respectively, was also similar. Furthermore, there were no differences between the two rat lines in the allosteric interactions between GABA and the benzodiazepine binding sites (labeled with [3H]flunitrazepam) in all three areas tested or the Type I binding sites (labeled with [3H]zolpidem) in the hippocampus. In contrast, RLA/Verh rats showed a significant reduction in the allosteric interactions between GABA and [3H]zolpidem binding sites in the cortex. As a whole, these results indicate the absence of generalized between-line differences in the GABA(A) receptor complex showing, at the same time, the existence of some specific differences in allosterism within the GABA(A) complex. These differences may contribute to the divergent emotional responses which characterize the RHA/Verh and RLA/Verh rat lines.

Long-term behavioural and neuroendocrine changes in Roman high-(RHA/Verh) and low-(RLA-Verh) avoidance rats following neonatal handling

Roman high-(RHA/Verh) and low-(RLA/Verh) avoidance rats, originally selected and bred for rapid vs poor acquisition of a two-way active avoidance response, differ in emotional reactivity and coping style. These differences are associated with particular neuroendocrine and neurochemical characteristics. New data are presented here to show that the behavioural changes specifically induced by neonatal handling, i.e. decreased emotional reactivity, are associated with marked changes in the neuroendocrine responses of (hyperemotional) RLA/Verh rats to a novel environment. Eight months after neonatal handling, self-grooming behaviour, a reliable marker of emotional reactivity in this line of rats, was significantly decreased in RLA/Verh rats. Defecation scores were also significantly reduced in both lines. Moreover, there was a significant reduction in prolactin and corticosterone release following exposure to a novel environment in neonatally-handled RLA/Verh rats as compared to control, non-handled rats. No effects on prolactin and corticosterone release were observed in RHA/Verh rats. There was also no apparent effect of neonatal handling on coping style i.e. RLA/Verh rats did not increase their spontaneous exploration of novel environments. Thus, the phenotypic expression of basic traits of (high) neuroendocrine/emotional reactivity was specifically modulated by neonatal handling in RLA/Verh rats, whereas both the (hypoemotional) RHA/Verh rats as well as coping style in both lines remained unaffected. Changes in emotional reactivity were still apparent at 12 months of age when rats from the same groups were tested for hyponeophagia. These results suggest that psychogenetically selected lines such as RHA/RLA rats are suitable animal models to investigate interactions between genes and the environment in determining individual sensitivity to stress and coping styles, as well as potential vulnerability (or resistance) to the development of maladaptive syndromes similar to anxiety and mood disorders in humans.

Amino Acid Effects on Post-Stress Ulcers: Relationship to Brain Serotonin, 5-HIAA and Norepinephrine

To replicate and extend results of earlier studies on amino acid effects on post-stress ulcers, rats were subjected to i.p. injections of (a) saline, (b) tryptophan, (c) tyrosine + valine or(d) tryptophan + tyrosine + valine, either 30 minutes before or immediately after one hour of water restraint stress. Gastric lesions, brain norepinephrine, serotonin and 5-hydroxyindoleacetic acid (5-HIAA) were examined after one hour of poststress rest. We hypothesised that post-stress lesions could be aggravated by central noradrenergic hypoactivity and serotonergic hyperactivity during the post-stress period. Other studies have indicated that tyrosine + valine reduces central serotonergic activity, while additional tryptophan blocks this effect. We therefore expected post-stress lesions to be reduced in tyrosine + valine but not in tryptophan + tyrosine + valine treated animals. Although these expectations were met tentatively in animals injected prior to stress, thus replicating tyrosine + valine effects we had observed earlier, opposite results were found in animals treated post-stress. The brain analyses indicate that the data cannot be explained by a norepinephrine/serotonin imbalance hypothesis. The time dependency of the effects underlines the need for caution in clinical applications of these amino acid treatments.

Changes in serotonergic measures in whole blood and various brain regions of rats administered with the 5-HT1A agonist tandospirone and/or exposed to electric foot-shock

We studied the effects of foot-shock on tryptophan, serotonin [5-hydroxytryptamine (5-HT)], and its metabolite, 5-hydroxyindole acetic acid (5-HIAA) in whole blood and various brain regions of rats pretreated with tandospirone, a novel 5-HT1A receptor agonist. The administration of tandospirone did not result in changes in serotonergic measures, but stress or stress plus the administration of tandospirone resulted in an increase in blood levels of tryptophan, 5-HT, and 5-HIAA. In animals given stress, tryptophan levels rose in every part of the brain, and in animals given stress and tandospirone, tryptophan levels increased in all the brain regions except the medulla. The administration of tandospirone alone did not give rise to changes in tryptophan levels in any part of the brain. The administration of tandospirone resulted in an increase in 5-HT levles in all brain regions except the cerebellum. In rats given stress and tandospirone, 5-HT levels increased in the hypothalamus, midbrain, and cortex relative to controls. In every part of the brain, the administration of tandospirone resulted in a decrease in the turnover rate of serotonin (5-HIAA/5-HT). In the presence of stress, the administration of tandospirone resulted in a decrease in the turnover rate of serotonin in hypothalamus, hippocampus, and midbrain compared with controls and stress alone. These results suggest that tandospirone may stimulate presynaptic receptors in the midbrain and inhibit the activity of monoamine oxidase, resulting in an increase in 5-HT levels in the serotonergic nerve terminals.

Cerebral tryptophan hydroxylase activity, and 5-HT1A receptor, 5-HT2A receptor, and 5-HT transporter binding in grouped and isolated Roman RHA and RLA rats: relationships with behaviours in two models of anxiety

Male Roman low-(RLA) and high-avoidance (RHA) rats differ when tested in the elevated plus-maze and the black/white box, but not when (isolated and) tested for their social interaction. Herein, we have analysed the impact of prior isolation on male Roman rats tested in the first two models of anxiety; moreover, because central serotonin (5-HT) systems in Roman rats have been scarcely studied, we have also analysed several anxiety-related indices of central serotonergic activity in grouped/isolated Roman rats. Group-housed RLA rats tested in the elevated plus-maze and the black/white box were less anxious than their RHA counterparts, thereby confirming our previous study. Isolation had anxiogenic (and hypolocomotor) effects, these being significant in RLA rats only. Tryptophan hydroxylase activity in midbrain (but not in cortex, hippocampus or hypothalamus) was lower in group-housed (but not in isolated) RLA rats than in RHA rats, a difference independent from changes in the regulatory properties of the enzyme. Neither midbrain and hippocampal [3H]8-hydroxy-2-(di-n-propylamino)-tetrlin binding at 5-HT1A receptors, nor midbrain [3H] citalopram binding at the 5-HT transporter was different between grouped/isolated RHA/RLA rats. Alternatively, a trend toward a lower hypothalamic [3H]citalopram binding in (group-housed) RLA rats than in RHA rats could be noted, whereas cortical [3H]ketanserin binding at 5-HT2A receptors was lower in RLA rats than in RHA rats, a difference prevented by prior isolation. This study opens the possibility that inter-line differences in 5-HT2A receptors partly (or totally) underlie the respective behaviours of RHA and RLA rats in the elevated plus-maze and the black/white box.

Amino acids, serotonin, and 5-hydroxyindoleacetic acid following foot shock in rats

Concentrations of tryptophan, serotonin (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) in brain and plasma, as well as plasma amino acid composition, were measured after 1-h foot shock. Stress induced a rise in both plasma and brain 5-HIAA, whereas 5-HT concentration was found to be increased only in plasma. A prominent rise in brain tryptophan was observed, whereas in plasma, foot shock caused a significant increase only in tryptophan level. Concentrations of other amino acids were found to be either decreased or unchanged. Ratio of tryptophan to the other long-chain neutral amino acids increased significantly following foot shock. It is possible that stress-related changes in 5-HT turnover are due to increased plasma tryptophan, in turn causing a rise in brain tryprophan, necessary to cope with enhanced 5-HT metabolism, reflected as a rise in 5-HIAA levels.

Stress and/or tranylcypromine treatment affects serotonergic measures in blood and brain in rats

Since stress can alter serotonin (5-hydroxytryptamine, 5-HT) turnover in the brain and the periphery, the effects of different types of acute stress on serotonin and related substances in the whole blood and various brain areas in rats pretreated with tranylcypromine (TCP) were studied. TCP administered alone caused a rise in 5-HT, a fall in its metabolite (5-hydroxyindoleacetic acid, 5-HIAA) in the whole blood and in every part of the brain analyzed relative to controls. In rats given TCP and subjected to footshock or water-immersion restraint stress similar changes, but to a different extent, were observed. 5-HT level remained essentially constant except in the blood and the limbic system, whereas 5-HIAA level was found to be increased in the blood and the brain, mainly in the limbic system and the brainstem following footshock. Water-immersion restraint stress caused an increase in 5-HT only in the limbic system without any changes in 5-HT and 5-HIAA in the blood. Relative to controls, an increase in total tryptophan concentration in the whole blood and in every part of the brain was found only after footshock application with or without pretreatment with TCP. In conclusion, responses to stress in rats may depend upon the type of stimulus applied as well as of a concurrent administration of TCP. Some regional differences may account for an altered in vivo efficacy of this drug.

GABAergic and dopaminergic transmission in the brain of Roman high-avoidance and Roman low-avoidance rats

The GABAergic and dopaminergic pathways in the central nervous system (CNS) play a pivotal role in the control of emotions and in the adaptive responses to stressful stimuli. The present study was aimed at characterizing a range of biochemical markers of GABA- and dopamine-mediated neurotransmission in the CNS of Roman high-avoidance (RHA/Verh) and Roman low-avoidance (RLA/Verh) rats, two psychogenetically selected lines that differ in their level of emotionality. The stimulatory effect of GABA on 36Cl- uptake was less pronounced in the cerebral cortex of RLA/Verh rats as compared to RHA/Verh rats, whereas no line-related changes were detected in [3H]GABA and [3H]flunitrazepam binding. On the other hand, the density of D1 dopamine receptors labeled with [3H]SCH 23390 was lower in the nucleus accumbens of RLA/Verh rats as compared to their RHA/Verh counterparts, whilst no line-dependent changes were observed in the binding parameters of D1 dopamine receptors in the striatum, amygdala, and prefrontal cortex. These biochemical differences may contribute to the distinct emotionality and responsiveness to the effects of psychoactive drugs of RHA/Verh and RLA/Verh rats.

Prolactin as a link between behavioral and immune differences between the Roman rat lines

Roman high (RHA)- and low (RLA)-avoidance rats are two lines of Wistar rats genetically selected on the basis of their active avoidance behavior in a shuttle-box. They also differ in several other behavioral responses, such as their locomotor activity in novel environments (open-field, circular corridor), with the RHA rats being more active than the RLA animals, as well as in endocrine reactivity and immune functions. These experiments were designed to investigate further the neuroendocrine characteristics of these animals as a possible link between the brain and immune functions. Despite the marked behavioral and immune differences observed, no between-lines variation could be found in basal hypothalamo-pituitary-adrenocortical axis activity or in its responses to different protocols of novel environment stress, or after corticotropin-releasing factor (CRF) challenge. On the other hand, stimulated prolactin levels were higher in the low avoidance line. These results exclude the pituitary-adrenocortical axis and suggest prolactin as a link between behavioral and immune differences between the Roman lines. Moreover, these results indicate that these rats may be an excellent model for the study of the relationships between the brain and the immune system.

The Roman strains of rats as a psychogenetic tool for pharmacological investigation of working memory: example with RU 41656

This study examined the effects of RU 41656, a dopaminergic D2 agonist, on the differential working memory performances and on the differential activities of the neurochemical systems of the Roman high (RHA) and Roman low (RLA) avoidance strains of rats. Compared with RLA, RHA performed worse in three tests of working memory (spontaneous alternation, radial maze and object recognition) and had higher levels of exploratory locomotor activity. Hippocampal and frontal cortex choline acetyltransferase (ChAT) activities were lower in RHA. Frontal cortex DA and DOPAC levels, hippocampal and striatal 5-HT and NA levels were higher in RHA. RU 41656 induced a significant improvement in working memory performance of RHA, whereas in RLA it had no effect. It decreased exploratory locomotor activity in both strains. ChAT activity in hippocampus was not affected by RU 41656 in either strain, whereas in frontal cortex it was increased in RHA but not in RLA. Hippocampal NA levels were decreased by RU 41656 in RHA but not in RLA. These results confirm previous data concerning the promnesic effect of RU 41656 and extend the finding that the Roman strains are a psychogenetic model for the behavioural, neurochemical and psychopharmacological study of the working memory in rats.

Roman strains as a psychogenetic model for the study of working memory: behavioral and biochemical data

Performances of male rats of the Roman High- (RHA), Roman Control- (RCA) and Roman Low- (RLA) Avoidance strains were compared in two working memory tests, a spatial one, the radial maze, and a nonspatial one, an object recognition test. The same rats were subjected to measures of emotional reactivity and of different forms of motor activity and finally to measures of cholinergic and aminergic activities in the hippocampus, frontal cortex and striatum. Compared to RHA, RLA performed better in the two working memory tests, displayed "anxiety" and had also lower levels of exploratory locomotor activity. Hippocampal ChAT activity was higher in RLA than in RHA. Levels of DA and DOPAC in the striatum were higher in RLA compared to RHA, whereas in the frontal cortex they were lower. For most of these measures, RCA were intermediate between RLA and RHA. These results confirm and extend the finding that the Roman strains are not only a genetic model for two-way avoidance conditioning but also for working memory.

Different responsiveness of spleen lymphocytes from two lines of psychogenetically selected rats (Roman high and low avoidance)

Roman high- (RHA) and low-avoidance (RLA) rats have been genetically selected on the basis of their active avoidance behavior, and have been shown to differ on numerous behavioral, neurochemical and neuroendocrine parameters, especially in response to stress. We investigated the activity of splenic lymphocytes in vitro. Natural killer cell activity against YAC-1 tumoral cells and the mitotic response to plant lectins concanavalin A and phytohemagglutinin were much lower for lymphocytes isolated from RHA rats, in males as well as in females. The difference between the two strains was even larger when measured in a stressed state, immediately after active avoidance learning. On the other hand, the mitotic response to bacterial lipopolysaccharide, a B-cell-specific mitogen, was not different between the two lines, indicating that the difference in lymphocyte reactivity is limited to the T-lineage. The lower activity of T-cells in the RHA line had no consequence upon the ability of these animals to build up an antibody response against sheep red blood cells. These results indicate that Roman lines are an interesting animal model for the study of the relationships between the brain and the immune system, as well as for the analysis of the genes involved in the control of behavior.

Specific effects of punishment on biogenic monoamine turnover in discrete rat brain regions

Specific effects of punishment on the turnover rates of norepinephrine, dopamine and serotonin (5-HT) in brain regions were investigated in rats exposed to punishment. Two yoked controls were also used in an attempt to separate the non-specific effects of response rate, reinforcement density and direct effects of punisher (foot shock). Punished and unpunished littermate rats had similar response rates, and the reinforcement density was almost identical for both groups. A third group (yoked-shock rats) received food and shock independent of responding whenever these were given to the punished rats. When compared to the unpunished rats, changes in the monoamine turnover rates resulting from the punishment were similar to the effects of yoked-shock with respect to the direction of action in most cases (13 out of 17 changes). These changes may be related to non-specific effects of the shock. Four changes by the punishment were determined to be specific effects of the punishment since the yoked-shock had no effect or changed the turnover to the opposite direction. Among these, increase in 5-HT turnover rate in the frontal cortex (greater than 7-fold) was the largest change. These results and reported effects of drugs which act on serotonergic systems on the punished behavior suggest that the increase in 5-HT neuronal activity in the frontal cortex is involved in the behavioral suppression induced by the punishment.

Genetic and environmental influences on behavioral and neurochemical aspects of emotionality in rats

Three pairings of rats (two derived from divergent, selective breeding and one from divergent environmental conditions) were compared with regard to behavioral and hormonal parameters. Striking differences were observed: results obtained in our own laboratory as well as those found in a review of the literature pointed to higher emotionality (e.g., increased defecation and corticosterone secretion, etc.) in Roman low-avoidance, Wistar-Kyoto and group-housed rats, as compared to their respective counterparts, Roman high-avoidance, spontaneously hypertensive, and individually housed Wistar rats. Concomitant receptor binding studies reviewed here (3H-diazepam- and 3H-imipramine-binding sites) have revealed, however, less consistent intrapair differences.

Masticatory muscle hyperactivity in temporomandibular disorders: is it an extrapyramidally expressed disorder?

Masticatory muscle hyperactivity appears to have an important role in temporomandibular disorders. A pathophysiological model for masticatory muscle hyperactivity is proposed that is centrally mediated, yet maintains support for present peripheral causes and therapies. In this hypothesis, masticatory muscle hyperactivity represents a mild extrapyramidal disorder distantly related to orofacial dyskinesias. Experimental evidence suggests a neurotransmitter imbalance in the basal ganglia, involving dopaminergic preponderance, or cholinergic and GABA-nergic hypofunction as the underlying cause.

The propensity for schedule-induced polydipsia is related to differences in conditioned avoidance behaviour and in defense reactions in a defeat test

In line with previous research showing that animals predisposed to develop schedule-induced polydipsia when submitted to intermittent distribution of food show differential behavioural and neurochemical characteristics, the present experiments investigated the nature of defense reactions to aversive situations in rats that do or do not develop schedule-induced polydipsia. It was found that rats that engage in excessive drinking during intermittent feeding display more rapid active avoidance learning in a 2-way shuttle-box and show less freezing when confronted with an aggressive resident male in a defeat test than those that do not develop schedule-induced polydipsia. These results are consistent with the hypothesis that individual differences in the propensity to exhibit oral consummatory activities in conditions of mild stress are related to the ability to shift behavioural programmes in response to external stimulation.

Effect of combined or separate administration of piracetam and choline on learning and memory in the rat

Different groups of rats received combined or separate administration of different doses of piracetam (P1:100, P2:200, and P4:400 mg/kg) and choline (C1:100 and C2:200 mg/kg). Compared to control treatment, C1 significantly improved performance in a delayed alternation (DA) task, while P1, P2, P4 or P1C1 had no effect. Moreover, rats receiving P2C1 and P4C1 were significantly inferior in acquiring DA to rats receiving the vehicle or separate administration of P1, P2 or C1. The different treatments with combined or separate administration of P and C had no effect on spontaneous locomotor activity and two-way avoidance conditioning. In a recognition-task only groups C1 and P4 were able to discriminate between familiar and new objects. The combined or separate administration of P1 and C1 on NA, DA, DOPAC, 5-HT, 5-HIAA levels, CAT activity and choline uptake were measured in frontal cortex and hippocampus: the only significant effect was a 5-HT increase in the hippocampus of rats treated with C1.

Changes in plasma corticosterone and cerebral biogenic amines and their catabolites during training and testing of mice in passive avoidance behavior

Concentrations of cerebral biogenic amines and their catabolites, and of plasma corticosterone were determined 10 min after training and testing of passive avoidance behavior in mice. Training and testing of mice that had acquired the task well resulted in statistically significant increases of plasma corticosterone, of the DOPAC:DA ratio [an index of dopamine (DA) metabolism] in prefrontal cortex, and of MHPG:NE ratios [an index of norepinephrine (NE) metabolism] in hypothalamus and brain stem. There were also decreases of NE in hypothalamus and brain stem, and an increase of 5-HIAA:5-HT [an index of serotonin (5-HT) metabolism] and of tryptophan in brain stem. Some of these changes also occurred in mice merely exposed to the apparatus but not trained. Plasma corticosterone concentrations were significantly higher in mice that performed the task well compared to those that did not, and there were significant correlations between this measure and the avoidance performance. Although there was only one statistically significant correlation between a cerebral metabolite and the avoidance performance (a decrease in hypothalamic NE), there were indications of relationships between cerebral biogenic amine metabolism and the performance. The patterns of neurochemical and endocrine changes closely resemble those previously observed in response to various stressors. Thus, the changes could reflect stress responses, which may or may not be related directly to the performance of the avoidance task.

Self-biting with multiple finger amputations following spinal cord injury

We have observed mutilative self-biting leading to multiple finger amputations in two patients following C4 complete spinal cord injury (SCI). Both men were of normal intelligence without psychosis and each had a neurotic personality and history of fingernail biting. They related the self-biting to anxiety and depression. We believe these to be the first English language reports of multiple finger amputations due to self-biting following SCI.

Evidence for species differences between rats and gerbils in striatal dopamine content and dopamine metabolism

High-performance liquid chromatography revealed significantly higher striatal concentrations of dopamine and homovanillic acid (HVA) in 9 male Mongolian gerbils than in 6 male Long-Evans rats. 5-Hydroxyindoleacetic acid concentrations were higher in rats, while no significant between-species difference was found with respect to 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin or protein concentrations. In gerbils, HVA and DOPAC occurred in approximately equal concentrations, suggesting that the formation of HVA may be of greater significance for the termination of transmitter function in the gerbil than in the rat.

The role of noradrenaline in tuning and dopamine in switching between signals in the CNS

Neuronal catecholaminergic activity modulates central nervous function. Specifically noradrenaline can exert a tuning or biassing function whereby the signal to noise ratio is altered. Dopamine activity may promote switching between inputs and outputs of information to specific brain regions. It has been ten years since evidence for a tuning function was advanced for noradrenaline and in the last 5 years the switching hypothesis for dopamine has been tentatively put forward. Recent studies are reviewed to show that while catecholamine activity contributes to neural interactions in separate brain regions that give rise to the organization of different functions, their working principles may be common between species and independent of the nucleus of origin. Behavioral examples are discussed and an attempt is made to integrate this with evidence from intracellular recording studies. It is suggested that the tuning principle in noradrenergic systems is particularly important for the formation of associations and neural plasticity (interference control) and that the switching principle of dopaminergic systems modulates the timing, time-sharing and initiation of responses (program-control).

Alteration of convulsive threshold and conditioned avoidance response in mice fed diets containing contraceptive steroids

Female CD1 mice given the contraceptive steroids mestranol and norethynodrel (1:10) in the diet (0.0033%) for 4 months had a growth reduction of 20% when compared with mice fed a normal diet, and had lower convulsive thresholds when tested with the vitamin B6 antagonists 2,4-dimethyl-5-methyl-hydroxypyrimidine and thiosemicarbazide. In conditioned avoidance response (CAR) tests, mice fed the steroid-containing diets showed a decreased acquisition performance during all six sessions; however, mice fed the same diet supplemented with vitamin B6 (0.04%) performed as well during the last three sessions of the CAR tests as mice fed the normal diet.

Differential response to cholinergic stimulation in psychogenitically selected rat lines

Male and female rats of two lines psychogenetically selected for bipolar extremes in shuttle box avoidance were evaluated for tremor, salivation, chromodacryoorhea, and hypothermia following treatment with the muscarinic cholinergic agonist oxotremorine. Roman Low-Avoidance (RLA/Verh) rats exhibited more pronounced oxotremorine-induced tremor, chromodacryorrhea, and hypothermia than Roman High-Avoidance (RHA/Verh) rats. There was a sex difference only for a chromodacryorrhea response, with females exhibiting a greater response following oxotremorine than males. In a subsequent experiment using female rats of both rat lines, it was demonstrated that pre-treatment with the cholinergic antagonist scopolamine blocked oxotremorine-induced tremor, salivation and chromodacryorrhea responses in both rat lines and reduced the hypothermic effect observed in RLA/Verh rats (but not the much weaker hypothermia found in RHA/Verh rats) after oxotremorine injection. Pretreatment with the peripherally active cholinergic antagonist methscopolamine significantly reduced oxotremorine-induced salivation and chromocacryorrhea and somewhat decreased tremor and hypothermic responses in both rat lines. These results stand in contrast to the results of earlier research in which RHA/Verh rats exhibited greater behavioral depression in a tunnel maze than RLA/Verh rats following cholinergic manipulations. In view of evidence that these rat lines do not differ in number of muscarinic brain receptors, the present results may be due to genetic differences in other aspects of cholinergic neurotransmitter function, differences in the function of other neurochemical systems, or differences in the absorption, distribution, or metabolism of oxotremorine.