Stress and putative endogenous ligands for benzodiazepine receptors: the importance of characteristics of the aversive situation and of differential emotionality in experimental animals

Acute stress causes sex-dependent changes to ventral subiculum synapses, circuitry, and anxiety-like behavior

Experiencing a single severe stressor is sufficient to drive sexually dimorphic psychiatric disease development. The ventral subiculum (vSUB) emerges as a site where stress may induce sexually dimorphic adaptations due to its sex-specific organization and pivotal role in stress integration. Using a 1-hr acute restraint stress model, we uncover that stress causes a net decrease in vSUB activity in females that is potent, long-lasting, and driven by adrenergic receptor signaling. By contrast, males exhibit a net increase in vSUB activity that is transient and driven by corticosterone signaling. We further identified sex-dependent changes in vSUB output to the bed nucleus of the stria terminalis and in anxiety-like behavior in response to stress. These findings reveal striking changes in psychiatric disease-relevant brain regions and behavior following stress with sex-, cell-type, and synapse-specificity that contribute to our understanding of sex-dependent adaptations that may shape stress-related psychiatric disease risk.

Contribution of the Roman rat lines/strains to personality neuroscience: neurobehavioral modeling of internalizing/externalizing psychopathologies

The Roman high-avoidance (RHA) and low-avoidance (RLA) rat lines/strains were established in Rome through bidirectional selection of Wistar rats for rapid (RHA) or extremely poor (RLA) acquisition of a two-way active avoidance task. Relative to RHAs, RLA rats exhibit enhanced threat sensitivity, anxiety, fear and vulnerability to stress, a passive coping style and increased sensitivity to frustration. Thus, RLA rats' phenotypic profile falls well within the "internalizing" behavior spectrum. Compared with RLAs and other rat strains/stocks, RHAs present increased impulsivity and reward sensitivity, deficits in social behavior and attentional/cognitive processes, novelty-induced hyper-locomotion and vulnerability to psychostimulant sensitization and drug addiction. Thus, RHA rats' phenotypes are consistent with a "disinhibiting externalizing" profile. Many neurobiological/molecular traits differentiate both rat lines/strains. For example, relative to RLA rats, RHAs exhibit decreased function of the prefrontal cortex (PFC), hippocampus and amygdala, increased functional tone of the mesolimbic dopamine system, a deficit of central metabotropic glutamate-2 (mGlu2) receptors, increased density of serotonin 5-HT2A receptors in the PFC, impairment of GABAergic transmission in the PFC, alterations of several synaptic markers and increased density of pyramidal immature dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. We review evidence supporting RLA rats as a valid model of anxiety/fear, stress and frustration vulnerability, whereas RHA rats represent a promising translational model of neurodevelopmental alterations related to impulsivity, schizophrenia-relevant features and comorbidity with drug addiction vulnerability.

Neurobehavioral and neurodevelopmental profiles of a heuristic genetic model of differential schizophrenia- and addiction-relevant features: The RHA vs. RLA rats

The Roman High- (RHA) and Low-(RLA) avoidance rat lines/strains were generated through bidirectional selective breeding for rapid (RHA) vs. extremely poor (RLA) two-way active avoidance acquisition. Compared with RLAs and other rat strains/stocks, RHAs are characterized by increased impulsivity, deficits in social behavior, novelty-induced hyper-locomotion, impaired attentional/cognitive abilities, vulnerability to psychostimulant sensitization and drug addiction. RHA rats also exhibit decreased function of the prefrontal cortex (PFC) and hippocampus, increased functional activity of the mesolimbic dopamine system and a dramatic deficit of central metabotropic glutamate-2 (mGlu2) receptors (due to a stop codon mutation at cysteine 407 in Grm2 -cys407*-), along with increased density of 5-HT2A receptors in the PFC, alterations of several synaptic markers and increased density of pyramidal "thin" (immature) dendrític spines in the PFC. These characteristics suggest an immature brain of RHA rats, and are reminiscent of schizophrenia features like hypofrontality and disruption of the excitation/inhibition cortical balance. RHA rats represent a promising heuristic model of neurodevelopmental schizophrenia-relevant features and comorbidity with drug addiction vulnerability.

Revisiting the role of anxiety in the initial acquisition of two-way active avoidance: pharmacological, behavioural and neuroanatomical convergence

Two-way active avoidance (TWAA) acquisition constitutes a particular case of approach -avoidance conflict for laboratory rodents. The present article reviews behavioural, psychopharmacological and neuroanatomical evidence accumulated along more than fifty years that provides strong support to the contention that anxiety is critical in the transition from CS (conditioned stimulus)-induced freezing to escape/avoidance responses during the initial stages of TWAA acquisition. Thus, anxiolytic drugs of different types accelerate avoidance acquisition, anxiogenic drugs impair it, and avoidance during these initial acquisition stages is negatively associated with other typical measures of anxiety. In addition behavioural and developmental treatments that reduce or increase anxiety/stress respectively facilitate or impair TWAA acquisition. Finally, evidence for the regulation of TWAA acquisition by septo-hippocampal and amygdala-related mechanisms is discussed. Collectively, the reviewed evidence gives support to the initial acquisition of TWAA as a paradigm with considerable predictive and (in particular) construct validity as an approach-avoidance conflict-based rodent anxiety model.

A Genetic Model of Impulsivity, Vulnerability to Drug Abuse and Schizophrenia-Relevant Symptoms With Translational Potential: The Roman High- vs. Low-Avoidance Rats

The bidirectional selective breeding of Roman high- (RHA) and low-avoidance (RLA) rats for respectively rapid vs. poor acquisition of active avoidant behavior has generated two lines/strains that differ markedly in terms of emotional reactivity, with RHA rats being less fearful than their RLA counterparts. Many other behavioral traits have been segregated along the selection procedure; thus, compared with their RLA counterparts, RHA rats behave as proactive copers in the face of aversive conditions, display a robust sensation/novelty seeking (SNS) profile, and show high impulsivity and an innate preference for natural and drug rewards. Impulsivity is a multifaceted behavioral trait and is generally defined as a tendency to express actions that are poorly conceived, premature, highly risky or inappropriate to the situation, that frequently lead to unpleasant consequences. High levels of impulsivity are associated with several neuropsychiatric conditions including attention-deficit hyperactivity disorder, obsessive-compulsive disorder, schizophrenia, and drug addiction. Herein, we review the behavioral and neurochemical differences between RHA and RLA rats and survey evidence that RHA rats represent a valid genetic model, with face, construct, and predictive validity, to investigate the neural underpinnings of behavioral disinhibition, novelty seeking, impulsivity, vulnerability to drug addiction as well as deficits in attentional processes, cognitive impairments and other schizophrenia-relevant traits.

Neonatal handling decreases unconditioned anxiety, conditioned fear, and improves two-way avoidance acquisition: a study with the inbred Roman high (RHA-I)- and low-avoidance (RLA-I) rats of both sexes

The present study evaluated the long-lasting effects of neonatal handling (NH; administered during the first 21 days of life) on unlearned and learned anxiety-related responses in inbred Roman High- (RHA-I) and Low-avoidance (RLA-I) rats. To this aim, untreated and neonatally-handled RHA-I and RLA-I rats of both sexes were tested in the following tests/tasks: a novel object exploration (NOE) test, the elevated zero maze (ZM) test, a “baseline acoustic startle” (BAS) test, a “context-conditioned fear” (CCF) test and the acquisition of two-way active—shuttle box—avoidance (SHAV). RLA-I rats showed higher unconditioned (novel object exploration test -“NOE”-, elevated zero maze test -“ZM”-, BAS), and conditioned (CCF, SHAV) anxiety. NH increased exploration of the novel object in the NOE test as well as exploration of the open sections of the ZM test in both rat strains and sexes, although the effects were relatively more marked in the (high anxious) RLA-I strain and in females. NH did not affect BAS, but reduced CCF in both strains and sexes, and improved shuttle box avoidance acquisition especially in RLA-I (and particularly in females) and in female RHA-I rats. These are completely novel findings, which indicate that even some genetically-based anxiety/fear-related phenotypes can be significantly modulated by previous environmental experiences such as the NH manipulation.

Coping style and stress hormone responses in genetically heterogeneous rats: comparison with the Roman rat strains

The purpose of the present study was to evaluate for the first time the stress-induced hypothalamus-pituitary-adrenal (HPA), adrenocorticotropic hormone (ACTH), corticosterone and prolactin responses of the National Institutes of Health genetically heterogeneous rat stock (N/Nih-HS rats) in comparison with responses of the relatively high and low stress-prone Roman Low- (RLA-I) and High-Avoidance (RHA-I) rat strains. The same rats were also compared (experiment 1) with respect to their levels of unconditioned anxiety (elevated zero-maze test), novelty-induced exploratory behavior, conditioned fear and two-way active avoidance acquisition. In experiment 2, naive rats from these three strains/stocks were evaluated for "depressive-like" behavior in the forced swimming test. N/Nih-HS and RLA-I rats showed significantly higher post-stress ACTH, corticosterone and prolactin levels than RHA-I rats. N/Nih-HS rats also presented the highest context-conditioned freezing responses, extremely poor two-way avoidance acquisition and very low novelty-induced exploratory behavior. Experiment 2 showed that, compared to RHA-I rats, N/Nih-HS and RLA-I rats displayed significantly less struggling (escape-directed) and increased immobility responses in the forced swimming test. Factor analysis of data from experiment 1 showed associations among behavioral and hormonal responses, with a first factor comprising high loadings of elevated zero-maze variables and lower loadings of conditioned fear, two-way avoidance acquisition and hormonal measures, while a second factor mainly grouped conditioned fear and two-way avoidance acquisition with novelty-induced exploration and post-stress prolactin. Thus, regarding their anxiety/fearfulness, passive coping style, "depressive-like" and stress-induced hormonal responses the N/Nih-HS rats resemble the phenotype profiles of the relatively high-anxious and stress-prone RLA-I rat strain.

Corticosterone urinalysis and nicotinic receptor modulation in rats

A routine method of measuring circulating corticosterone (CORT) levels in rats involves sampling of plasma from cannulated animals. However, being somewhat invasive, this method can potentially be confounded by its inherently stressful nature. This study investigated the feasibility of measuring corticosterone using a non-invasive sampling method from voided urine of male rats. Reliability was assessed pharmacologically with nicotinic compounds previously demonstrated to modulate plasma glucocorticoid levels. Nicotine (0.1-1mg/kg sc) dose-dependently increased corticosterone levels in rat urine at 30-70 min following administration. The short-lived nature of this elevation was confirmed as CORT levels measured 6 and 24h later were shown to have returned to basal levels. Both basal and nicotine-induced (0.5mg/kg sc) elevations in urinary CORT were consistent between groups of animals with weights ranging from 200 to 400 g. The magnitude of urinary CORT elevation induced by nicotine (0.5mg/kg sc) was found to be similar to that induced by a forced swim stressor in male Lister ) antagonist mecamylamine (0.05-0.5mg/kg sc) dose-dependently reversed the effects of nicotine (0.5mg/kg sc) on urinary CORT. Finally, the alpha(4)beta(2)-subunit preferring agonist TC-2559 induced a dose-dependent increase in CORT, whereas alpha(7)- and beta(4)-subunit preferring ligands had no effect, suggestive of the potential for differential involvement of nicotinic receptor subtypes in the mediation of this response. In conclusion, urinary corticosterone sampling in rats represents a robust assay sensitive to experimental manipulations of both pharmacological and behavioural relevances.

Characterization of central and peripheral components of the hypothalamus-pituitary-adrenal axis in the inbred Roman rat strains

Several studies performed in outbred Roman high- and low-avoidance lines (RHA and RLA, respectively) have demonstrated that the more anxious line (RLA) is characterized by a higher hypothalamic-pituitary-adrenal (HPA) response to certain stressors than the less anxious one (RHA). However, inconsistent results have also been reported. Taking advantage of the generation of an inbred colony of RLA and RHA rats (RHA-I and RLA-I, respectively), we have characterized in the two strains not only resting and stress levels of peripheral HPA hormones but also central components of the HPA axis, including CRF gene expression in extra-hypothalamic areas. Whereas resting levels of ACTH and corticosterone did not differ between the strains, a greater response to a novel environment was found in RLA-I as compared to RHA-I rats. RLA-I rats showed enhanced CRF gene expression in the paraventricular nucleus (PVN) of the hypothalamus, with normal arginin-vasopressin gene expression in both parvocellular and magnocellular regions of the PVN. This enhanced CRF gene expression is not apparently related to altered negative corticosteroid feedback as similar levels of expression of brain glucorticoid and mineralocorticoid receptors were found in the two rat strains. CRF gene expression tended to be higher in the central amygdala and it was significantly higher in the dorsal region of the bed nucleus of stria terminalis (BNST) of RLA-I rats, while no differences appeared in the ventral region of BNST. Considering the involvement of CRF and the BNST in anxiety and stress-related behavioral alterations, the present data suggest that the CRF system may be a critical neurobiological substrate underlying differences between the two rat strains.

Fearfulness in a large N/Nih genetically heterogeneous rat stock: differential profiles of timidity and defensive flight in males and females

Anxiety-related behaviors were evaluated across various tests in a large sample (n=787, both sexes) of genetically heterogeneous (N/Nih-HS) rats, derived from an eight-way cross of inbred strains. These tests either evoke unlearned (black-white box, BWB-; novel-cage activity, NACT-; elevated "zero" maze, ZM-; baseline acoustic startle response, BAS-) or learned (fear-potentiated startle, FPS-; two-way active-shuttle box-avoidance acquisition, SHAV-) anxious/fearful responses. The results showed that, with the exception of fear-potentiated startle, almost all (unlearned and learned) behaviors assessed fit with a pattern of sex effects characterized by male rats as being more fearful than females. We applied factor analyses (oblique rotation) to each sex, with the final two-factor solution showing: (1) a first factor (labelled as "Timidity") comprising BWB, NACT and ZM variables in both sexes, plus SHAV responding in the case of males, and (2) a second factor (called "Defensive Flight") which grouped BAS, FPS, and SHAV responding in both sexes. An additional regression analysis showed significant influences of (unlearned) risk assessment (i.e. stretch-attendance) behavior on SHAV in males, while FPS was the main variable positively influencing SHAV (in the intermediate and advanced phases of acquisition) in females. This indicates, for the first time, that fear-potentiated startle may have a facilitating role in the rat's active responses (at least in females) to the cue in the intermediate to advanced phases (i.e. when the initial "passive avoidance/active avoidance" begins to fade) of shuttle box avoidance acquisition. The results of this first extensive behavioral evaluation of N/Nih-HS rats are discussed in terms of their potential usefulness for present and future neurobehavioral and genetic studies of fearfulness/anxiety.

Progesterone withdrawal effects in the open field test can be predicted by elevated plus maze performance

Allopregnanolone (3alpha-hydroxy-5alpha-pregnane-20-one) is a ring-A-reduced metabolite of progesterone, which is naturally produced during the luteal phase of the menstrual cycle, during pregnancy and by stressful events. The steroid hormone inhibits neural functions through increased chloride ion flux through the GABA(A) receptor. The effects and subsequent withdrawal symptoms are similar to those caused by alcohol, benzodiazepines and barbiturates. This study examined the withdrawal effects of progesterone with regards to the influence of individual baseline exploration and risk taking. Rats were tested on the elevated plus maze (EPM) before hormonal treatment, in order to evaluate differences in risk taking and exploration of open and elevated areas. Treatment consisted of ten consecutive once a day progesterone or vehicle s.c. injections. On the last day of treatment, estradiol was injected in addition to progesterone, followed by a 24-h withdrawal before testing in the open field test (OF). Progesterone-treated rats showed a withdrawal effect of open area avoidance in the OF. The vehicle-treated control rats showed strong correlations between the EPM and OF parameters. This relationship was not found for the progesterone group at withdrawal. Rats with greater numbers of open arm entrance in the EPM pretest showed an increased sensitivity to progesterone withdrawal (PWD) compared to rats with low exploration and risk taking. The results indicate that the effects of PWD relate to individual exploration and risk taking. Furthermore, the possible analogy of PWD and PMS/PMDD in relation to individual traits is discussed.

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.

Evaluation of perinatal flumazenil effects on the behavior of female RLA/Verh rats in anxiety tests and shuttle box avoidance

The present study investigated the effects of perinatal flumazenil (Ro 15-1788, a benzodiazepine receptor antagonist), given from gestational day 15 to the 14th day after giving birth, at two doses (3.5 and 6.3 mg/kg/ day) on the behavior of female RLA/Verh rats. This rat line has been selectively bred for non-acquisition of two-way active avoidance. Offspring of treated/non-treated dams were tested when adults for two-way active (shuttle box) avoidance acquisition. For comparison reasons additional offspring coming from the same treatments were used in an hyponeophagia test and in both an open field and a plus maze tests. The results show that perinatal flumazenil, specially the lower dose (and also the highest dose, although only in the final phases of the shuttle box training) was able to improve two-way active avoidance acquisition, as it has been previously found with males, whereas it failed to show any effect in the hyponeophagia task, the open field and the plus-maze tests. As two-way active avoidance acquisition can be enhanced both by reducing emotionality/anxiety or by improving memory, it is suggested that flumazenil treatment could have affected either one or both processes.

Ovarian steroids modify the behavioral and neurochemical responses of the central benzodiazepine receptor

The effect of ovarian steroids on the benzodiazepine receptor was assessed in the elevated plus-maze and, after restraint stress, in benzodiazepine receptor binding assays. Vehicle-treated proestrous rats displayed anxiolytic behavior, relative to diestrus or estrous rats. Anxiolytic behavior was observed after 1 or 2 mg/kg diazepam in diestrus and estrus. However, whereas 4 mg/kg increased open arm exploration in diestrus, a decrease in the same measure was found at estrus. At proestrus, a decrease in anxiolytic behavior was observed after 2 and 4 mg/kg. In ovariectomized vehicle-treated rats, restraint stress increased NaCl-induced potentiation of 3H-flunitrazepam binding in cortical and cerebellar, but not in hippocampal membranes. Estradiol benzoate (2 micrograms) prevented the potentiation of flunitrazepam binding by NaCl in nonstressed and stressed animals, whereas progesterone (0.5 mg) increased the NaCl-induced potentiation of flunitrazepam binding in both nonstressed and stressed animals. Combined estradiol benzoate and progesterone treatment produced effects that were intermediate to those seen after injection of either steroid alone. The potentiation of flunitrazepam binding by NaCl observed in vehicle-treated stressed or progesterone-treated nonstressed animals was mimicked in vitro by addition to reaction test tubes of the neuroactive metabolite of progesterone, 3 alpha-hydroxy-5 alpha-pregnan-20-one (allopregnanolone). These results point to a significant role of ovarian hormones in modifying the stress response of the benzodiazepine receptor.

Effects of prenatal diazepam on two-way avoidance behavior, swimming navigation and brain levels of benzodiazepine-like molecules in male Roman high- and low-avoidance rats

Utilizing psychogenetically selected Roman high- and low-avoidance rats (RHA/Verh and RLA/Verh), the present experiments investigated the effects of prenatally administered vehicle and diazepam (1 and 3 mg/kg per day, SC) on the behavior and neurochemistry of adult, male offspring. Active, two-way avoidance behavior was analyzed in 96 rats, at 6 months of age, and swimming navigation in 68 others, at 11 months. Three weeks after testing, selected brain areas from the latter animals were immunoassayed for benzodiazepine (BZD)-like molecules. The 3 mg/kg dose of diazepam both decreased freezing behavior in the shuttle box and reduced the hippocampal content of BZD-like molecules in the RLA/Verh male rats. Swimming navigation (spatial learning), at which the RLA/Verh rats were more adept, was not specifically affected by prenatal diazepam in either rat line. The possibility exists that an increased hippocampal release of BZD-like substances may be necessary to alter shuttle box behavior in RLA/Verh rats.

Postnatal handling reduces anxiety as measured by emotionality rating and hyponeophagia tests in female rats

The present studies evaluated the short- and long-lasting effects of postnatal handling (administered during the first 21 days of life) on the emotional behavior of female Sprague-Dawley rats. The performance of postnatally handled (H) and control nonhandled (NH) animals was compared in two different situations: an emotionality rating (ER) test (when they were 40 days or 4 months old), and a hyponeophagia (neophobia) test of anxiety, at the age of 4 months. The results showed that postnatal handling induced both short-term and long-term reductions of spontaneous emotional reactivity in the ER test, although the effects on some measures disappeared in 4-month-old rats. Postnatal handling also induced enduring decreases of anxiety as measured by the hyponeophagia test. None of the observed effects were attributable to changes in basal locomotor activity. ER measures were significantly related to hyponeophagia, because animals showing the highest emotionality scores in the ER test (preferentially NH animals) were those that showed the highest eating latencies and spent less time eating in the neophobic situation (i.e., hyponeophagia test).

Postnatal handling reduces emotionality ratings and accelerates two-way active avoidance in female rats

The present study evaluated whether postnatal handling (PH; administered daily during the first 21 days of life) could reduce anxiety or emotional reactivity in tasks of either spontaneous or conditioned fear-related behavior. To this purpose control nonhandled and postnatally handled female rats were submitted to three different behavioral tests: an emotionality rating (ER) followed by an elevated plus-maze test of anxiety in one experiment, and an acquisition of two-way active (shuttlebox) avoidance under two different training conditions in a separate experiment. Significant effects of PH treatment appeared in the three testing situations, clearly indicating an important and enduring reduction of emotionality/anxiety in PH-treated rats. Of special interest were the results of shuttlebox training: by shortening the conditioned stimulus (CS) and the intertrial interval (ITI) duration, avoidance acquisition was impaired as expected but the improving effects of PH were even more marked. The results are discussed in relation to previous studies reporting controversial results in the same (or similar) testing situations.

Chick imprinting performance and susceptibility to acute stress associated to flunitrazepam receptor increase

One-day-old chicks were selected on their performance in imprinting behaviour and termed high-imprinted (H-I), partially imprinted (P-I) and low-imprinted (L-I) chicks. Then, H-I and L-I chicks were submitted to acute handling stress and [3H]flunitrazepam receptor-binding was performed on synaptosomal membranes from forebrain at various times after handling. The receptor number significantly increased in L-I but not in H-I chicks at 30 min after handling while the affinity remained unchanged at all times. In addition, when the three selected groups were maintained to reach 15 days of age and then they were submitted to acute swimming stress, the degree of receptor increase was also inversely related to the degree of imprinting performance. The receptor increase associated to swimming stress was higher in the left hemisphere, suggesting an interhemispheric asymmetry of stress effects. The results suggest that more-imprinted chicks are less susceptible than less-imprinted chicks to acute stress associated to central benzodiazepine receptor increase, probably due to differences in the degree of endogenous emotionality.

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.

Housing conditions alter GABAA receptor of alcohol-preferring and -nonpreferring rats

The effects of housing conditions on some functional properties of the GABAA benzodiazepine (BZD) receptor in the cerebral cortex were examined in the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines of rats. Compared to rats housed in pairs (P with P and NP with NP), P and NP rats housed individually had 44% (p < 0.005) and 32% (p < 0.01) lower values, respectively, for GABA-stimulated 36Cl- influx into cortical microsacs. The maximal effect (Vmax) of flunitrazepam (FNZ) to enhance GABA-stimulated 36Cl- uptake was 44% higher in individually housed P rats than pair-housed P rats (p < 0.05) and 51% higher than individually housed NP rats (p < 0.05). There was no difference between single and pair-housed NP rats for Vmax values of FNZ enhancement of GABA-stimulated 36Cl- influx. The results show housing conditions can alter some of the functional properties of the GABAA/BZD receptor in the P and NP lines of rats. The differential effect of housing conditions on FNZ enhancement of 36Cl- influx, observed between the lines, may be a result of higher levels of anxiety being produced by brief isolation in the P rat.

Similar effects of ethanol and flumazenil on acquisition of a shuttle-box avoidance response during withdrawal from chronic ethanol treatment

1. Acquisition of a two-way shuttle-box avoidance response is facilitated by ethanol. This facilitated acquisition of an avoidance response to ethanol was attenuated during withdrawal from chronic-ethanol diet intake (i.e. tolerance developed by ethanol). The deficit in the avoidance task after chronic ethanol treatment could be overcome by increasing the dose of ethanol. 2. Flumazenil, a benzodiazepine antagonist, also facilitated acquisition of the avoidance response in control rats. This response to flumazenil was significantly reduced during withdrawal from chronic-ethanol treatment. This reduced avoidance responding during withdrawal also could be overcome by increasing the dose of flumazenil. 3. The benzodiazepine-inverse agonist, RO 15-4513, produced a deficit in avoidance responding that was antagonized by both ethanol and flumazenil in a dose-related manner. 4. To determine whether flumazenil has the properties of a benzodiazepine agonist, it was established that, unlike the benzodiazepine chlordiazepoxide, flumazenil did not enhance the ethanol-induced deficit in the aerial righting reflex. Additionally, flumazenil blocked the action of chlordiazepoxide in this procedure, consistent with the benzodiazepine antagonist action of flumazenil. 5. Data collected are consistent with the hypothesis that an endogenous substance with the properties of a benzodiazepine-inverse agonist antagonizes the anticonflict actions of acutely administered ethanol during withdrawal from chronic-ethanol exposure.

Postnatal handling, perinatal flumazenil, and adult behavior of the Roman rat lines

The effect of infantile handling stimulation and/or perinatal flumazenil (Ro 15-1788; a benzodiazepine receptor antagonist; 3.7 mg/kg/day) administration on exploratory and emotional-related behavior was investigated using adult females from the Roman high- and low-avoidance (RHA/Verh and RLA/Verh) lines. When rats (6 months old) were exposed to a hexagonal tunnel maze including an illuminated central arena, it was found that RHA/Verh rats were more active, explored more maze area, showed more outward preference, and more frequently entered the illuminated center than RLA/Verh rats. In addition, postnatal stimulation decreased emotional-related behavior in both lines of rats, as expressed by increased entry into, and time spent in, the central arena. Perinatal flumazenil treatment decreased entry into the maze central arena in both rat lines but this effect was counteracted by postnatal (handling) stimulation. Thus, the present study extends to adult RHA/Verh and RLA/Verh rats the positive long-lasting effects of postnatal handling and shows postnatal handling x flumazenil interactions in some behavioral parameters related to the pattern of exploration and exploratory efficiency.

Differential effects of early stimulation and/or perinatal flumazenil treatment in young Roman low- and high-avoidance rats

The effect of infantile handling-stimulation and/or perinatal flumazenil (3.7 mg/kg/day) administration on exploratory and emotional-related behavior was investigated using Roman high- and low-avoidance (RHA/Verh and RLA/Verh) rats. Postnatal handling increased exploration in 30-day-old rats of both psychogenetically selected lines when they were exposed to a hexagonal tunnel maze including an illuminated central arena. Likewise, postnatal stimulation decreased emotional reactivity in both lines of rats, as expressed by increased entry into the central arena, decreased defecation and vocalization frequency, but these effects were more pronounced in the RLA/Verh line. There were interactions between perinatal flumazenil treatment and rat line, indicating that flumazenil enhanced entry into the maze central arena in handled-RLA/Verh rats, whereas a tendency toward the opposite effect was observed in drug-treated and handled-RHA/Verh animals. Thus, the present study emphasizes that the effects of environmental manipulations are partly dependent upon genetic factors, and that pharmacological effects also depend on both genetic and environmentally-induced predisposition.

Infantile stimulation and the role of the benzodiazepine receptor system in adult acquisition of two-way avoidance behavior

The present study shows that postnatal "consistent" handling (CH) of rats had long-lasting improving effects on coping with an stressful task (i.e. two-way active avoidance), and that such effects were partially prevented by acute Ro 15-1788 (antagonist of benzodiazepine receptor-BZR; 5 mg/kg) administration. Long-lasting detrimental effects in the same task were also observed in rats which received postnatal "inconsistent" handling (INCH), effects that were slightly increased by acute Ro 15-1788 treatment. Finally, Ro 15-1788 tended to increase avoidance acquisition in non-handled (NH) animals. The observed effects of Ro 15-1788 could be partially attributed to a differential modulation of the process of avoidance acquisition depending on postnatal treatments producing different levels of emotionality.

Infantile (handling) stimulation and behavior in young Roman high- and low-avoidance rats

The effect of infantile handling stimulation on exploratory and emotional behavior of Roman high- and low-avoidance (RHA/Verh and RLA/Verh) weanling rats was investigated. Postnatally handled and nonhandled, 4-week-old males and females from both psychogenetically selected lines were exposed to a hexagonal tunnel maze, including an illuminated central arena. Postnatal handling increased exploratory behavior and decreased emotional reactivity as expressed by increased entries into the central arena and a reduction in defecations in both lines of rats. These effects were more pronounced in the RLA/Verh rats. In agreement with earlier studies using nonselected adult rats, the females of both lines (especially those from the RHA/Verh line) were more sensitive than males to the positive influences of early stimulation.