Aversive Situations Research Articles

Potentiated amygdaloid auditory-evoked potentials and freezing behavior after fear conditioning in mice

Elucidation of cellular and molecular mechanisms underlying fear-related memory would greatly benefit from the possibility of combined behavioral and electrophysiological recordings in genetically modified mice. As a first step to this goal, we implanted adult C57BL/6J mice with recording electrodes aimed at the basolateral amygdaloid complex and trained them in an auditory fear conditioning paradigm. After conditioning, animals with paired tone and footshock presentation showed not only intensified freezing behavior lasting for 2 days, but also increases, lasting 4 days, in slope and amplitude of the most negative component of auditory-evoked potentials triggered by the conditioned stimulus. These effects could not be observed in animals with unpaired tone and footshock presentation. Thus, our data show that a long-lasting association of a former neutral tone with an aversive situation is accompanied by a long-lasting increase of auditory-evoked potentials in freely moving mice. However, extinction of the potentiation of auditory-evoked potentials and freezing behavior followed different time courses, thus making a direct relationship between these responses unlikely.

Conditioned Taste Aversion and Ca/Calmodulin-Dependent Kinase II in the Parabrachial Nucleus of Rats

Bielavska and colleagues (Bielavska, Sacchetti, Baldi, & Tassoni, 1999) have recently shown that KN-62, an inhibitor of calcium/calmodulin-dependent kinase II (CaCMK), induces conditioned taste aversion (CTA) when introduced into the parabrachial nucleus (PBN) of rats. The aim of the present report was to assess whether activity of CaCMK in the PBN is changed during CTA. We induced CTA in one group of rats by pairing saccharin consumption with an ip injection of lithium chloride. Another group of rats received lithium alone (without being paired with saccharin consumption) to test whether lithium has an effect on CaCMK in the PBN, independent of those effects due to training. In animals receiving CTA training, CaCMK activity in extracts of PBN was reduced by approximately 30% at the postacquisition intervals of 12, 24, and 48 h, compared to control animals receiving saccharin with saline injection. By 120 h after CTA training, no effect on CaCMK was present. At those postacquisition intervals showing CaCMK activity effects due to CTA, there were no effects attributable to lithium alone. Lithium alone produced only a short-lasting reduction in CaCMK activity (at 20 min a 30% decrease, at 60 min a 23% decrease; and at 6, 12, and 24 h no decrease). The time course of lithium-induced effects differed markedly from that of CTA training. All changes were Ca2 ± -dependent; we did not observe any changes in Ca-independent activity. CTA effects on CaCMK were selective for PBN, insofar as we did not observe any CTA effects on CaCMK in the visual cortex, a brain region unrelated to taste pathways. Since CTA produces a relatively long-lasting reduction in CaCMK activity (lasting 2 days or more) specifically in the PBN, which is critical a relay for taste information, the reduction of CaCMK activity may enable the consolidation of taste memory in an aversive situation.

Um estudo correlacional entre habilidades sociais e traços de personalidade

Este trabalho teve como objetivo o desenvolvimento de um estudo correlacional entre habilidades sociais e traços de personalidade segundo o modelo dos cinco grandes fatores. Foram sujeitos da pesquisa 189 estudantes universitários, de ambos os sexos (41 homens e 148 mulheres), de 18 a 59 anos (média 26,3 anos), primeiro-anistas dos cursos de Letras, História, Psicologia, Pedagogia e Biologia. Foram aplicados o Inventário de Habilidades Sociais, que informa sobre (a) enfrentamento com risco, (b) auto-afirmação na expressão de afeto positivo, (c) conversação e desenvoltura social, (d) auto-exposição a desconhecidos e a situações novas e (e) auto-controle da agressividade a situações aversivas; e um Inventário de Personalidade que informa sobre os cinco grandes fatores: extroversão, socialização, escrupulosidade, neuroticismo e abertura para novas experiências. Encontrou-se que a variância de enfrentamento com risco pode ser explicada principalmente por extroversão e abertura para novas experiências; auto-afirmação na expressão de afetos positivos, por socialização e equilíbrio emocional; conversação e desenvoltura social, pelo conjunto equilibrado de todas os cinco grandes fatores, exceto escrupulosidade; auto-exposição a desconhecidos e a situações novas, por extroversão e equilíbrio emocional; e auto-controle da agressividade por socialização.

Prenatal glucocorticoid programming of brain corticosteroid receptors and corticotrophin-releasing hormone: possible implications for behaviour.

Glucocorticoids may underlie the association between low birth weight and adult disorders such as hypertension, type 2 diabetes and affective dysfunction. We investigated the behavioural and molecular consequences of two paradigms of prenatal dexamethasone administration in rats. Rats received dexamethasone (100 microg/kg per day) throughout pregnancy (DEX1-3), in the last third of pregnancy only (DEX3) or vehicle. Both dexamethasone treatments reduced birth weight, only DEX1-3 offspring had reduced body weight in adulthood. In adult offspring, both prenatal dexamethasone paradigms reduced exploratory behaviour in an open field. In contrast, only DEX3 reduced exploration in an elevated plus-maze and impaired behavioural responses and learning in a forced-swim test. This behavioural inhibition may reflect increased baseline corticotrophin-releasing hormone mRNA levels (30% higher) in the central nucleus of the amygdala in both dexamethasone-exposed groups. Adult DEX3 offspring also showed increased corticotrophin-releasing hormone mRNA with unaltered glucocorticoid receptor mRNA in the hypothalamic paraventricular nucleus and reduced hippocampal glucocorticoid- and mineralocorticoid receptor mRNA expression, suggesting reduced hippocampal sensitivity to glucocorticoid suppression of the stress axis. In contrast, DEX1-3 rats had no changes in hippocampal corticosteroid receptors, but showed increased mRNA levels for both receptors in the basolateral nucleus of the amygdala. From this data we suggest that prenatal glucocorticoid exposure programs behavioural inhibition perhaps via increased amygdalar corticotrophin-releasing hormone levels, while DEX3 also impairs coping and learning in aversive situations, possibly via altered hippocampal corticosteroid receptor levels. Overexposure to glucocorticoids, especially late in gestation, may explain the link between reduced early growth and adult affective dysfunction.

Contralateral Rotatory Bias in the Free-Swimming Test After Unilateral Hemispherectomy in Adult Swiss Mice

In the free-swimming rotatory test mice spend most of the time swimming close to the wall of the container attempting to escape from an aversive test situation. The attraction to the wall may suggest that turning behavior in the free-swimming test reflects the existence of intrinsic sensory asymmetries, which determine preferential attention adhesion to one side. In order to test this hypothesis, we investigated the rotatory swimming behavior of mice submitted to a unilateral hemispherectomy at adulthood, a condition of extreme sensory asymmetry. Fifteen days after surgery procedures, each mouse was tested for 5 min on 3 different days. We found that the hemispherectomized mice had a significant strong bias to turn in the direction contralateral to their lesion. These data could be explained considering that, in attempting to escape from the test situation, animals bring the recipient wall into their intact sensory field and, as a consequence, set the direction of locomotion. Thus, the free-swimming test may be useful to investigate sensory asymmetries during an aversive test situation.

Manejo de variáveis psicológicas no tratamento do câncer em crianças: algumas contribuições da psiconeuroimunologia

Estudos em psico-oncologia pediátrica apontam a necessidade de intervenções multiprofissionais sistemáticas que possam contribuir para a minimização de efeitos adversosproduzidospor diferentes situações do tratamentodo câncera que crianças e familiares são submetidos ou, preparar o paciente para enfrentar contextos identificados como de caráter estressante. O presente artigo apresenta os princípios básicos da psiconeuroimunologia e discute a funcionalidade de algumas contribuições desta área para o desenvolvimento de programas de apoio psicológico à crianças com câncer, que permitam a construção de um repertório comportamental e cognitivo apropriado ao enfrentamento de situações aversivas durante o período de tratamento da doença. Um exemplo de programa de apoio psicológico, desenvolvido em uma unidade de saúde do Distrito Federal é descrito.

Uncertainty of Outcomes as a Component of Active Coping

Abstract Control or control-belief is often viewed as being directly instrumental in facilitating active coping in aversive situations, and yet the empirical evidence for the effects of control is inconclusive. In this study we investigated the role of feedback and predictability in determining the effects of control-belief during an aversive reaction time task. Ninety-six subjects were allocated to one of eight conditions in a 2 × 2 × 2 control-belief by feedback by predictability factorial design. All subjects were matched in terms of the nature of the task and in the number and time of receipt of both the warning signal and noise. Heart rate reactivity and task performance (reaction time) were measured. Subjects who received feedback displayed greater phasic heart rate responses following the noise stimulus and smaller decreases in heart rate during the postimpact period than those without feedback, particularly in predictable conditions. Control-belief had no effect on heart rate responses. None of the factors led to better task performance. These findings are discussed in relation to processes of active coping and attentional processes of stimulus input, and the need for further studies examining the relative contributions of control-belief, feedback, and predictability in determining cardiovascular function is highlighted.

Role of corticotropin-releasing factor, vasopressin and the autonomic nervous system in learning and memory

Learning and memory are essential requirements for every living organism in order to cope with environmental demands, which enables it to adapt to changes in the conditions of life. Research on the effects of hormones on memory has focused on hormones such as adrenocorticotropic hormone (ACTH), glucocorticoids, vasopressin, oxytocin, epinephrine, corticotropin-releasing factor (CRF) that are released into the blood and brain following arousing or stressful experiences. Most of the information have been derived from studies on conditioned behavior, in particular, avoidance behavior in rats. In these tasks, an aversive situation was used as a stimulus for learning. Aversive stimuli are associated with the release of stress hormones and neuropeptides. Many factors play a role in different aspects of learning and memory processes. Neuropeptides not only affect attention, motivation, concentration and arousal or vigilance, but also anxiety and fear. In this way, they participate in learning and memory processes. Furthermore, neuropeptides such as CRF and vasopressin modulate the release of stress hormones such as epinephrine. In turn, systemic catecholamines enhance memory consolidation. CRF and vasopressin are colocalized in neurons from the nucleus paraventricularis, which project to nuclei in the brainstem involved in autonomic regulation. The objective of this paper is to discuss the role of CRF, vasopressin, and the autonomic nervous system (ANS) in learning and memory processes. Both CRF and vasopressin have effects in the same direction on behavior, learning and memory processes and stress responses (release of catecholamines and ACTH). These neuropeptides may act synergistically or in a concerted action aimed to learn to adapt to environmental demands.

Exploratory Activity of Rats in Three Different Environments

AbstractAdult male hooded (Long‐Evans) rats (Rattus norvergicus) were used to compare the efficiency of three types of tests (plain open field – OF, open field with a refuge – OD, and complex environment with a refuge – EX), for the evaluation of exploratory behaviour. The results confirmed that OF is a highly aversive situation with the animals showing elevated emotional response (defecation and urination) when compared to situations containing a refuge (OD and EX). Presence of a plain arena (OF and OD) does not elicit high exploratory performance, as shown by the delayed and reduced exit from the refuge in OD when compared to EX. Thus locomotor activity in OF (covered distance, number of rearings) probably reflects more of an escape reaction than a genuine exploratory behaviour. Conversely the presence of a complex environment seems to elicit a high exploratory performance expressed as a quick exit from the refuge, an increased time in the environment (more than 75% of the observation time) and intense locomotor patterns (large covered distances, great number of rearings) but with little emotional display (reduced defecation and urination). The results thus show the importance of considering ethological factors in the choice or development of laboratory tests.

Effects of exogenous serotonin on a motor behavior and shelter competition in juvenile lobsters (Homarus americanus).

Three experiments were conducted to determine (1) the pharmacodynamics of 5-hydroxytryptamine in juvenile lobsters; (2) the effects of 5-hydroxytryptamine, using a range of dosages, on a motor behavior used to escape an aversive situation; and (3) the effect of doses that did and did not inhibit this motor behavior on measures of dominance and shelter competition. The fate of 5-hydroxytryptamine in hemolymph over a 60-min post-injection period showed that the concentration fell rapidly to a low plateau that was maintained for at least 1 h. Low doses of 5-hydroxytryptamine did not affect locomotor behavior, but higher doses inhibited it. Dominance and subsequent possession of a shelter were unaffected by a low dose of 5-hydroxytryptamine but a higher dose that inhibited locomotion resulted in lobsters that lost fights and did not secure or retain possession of the shelter. In the context of dominance and shelter competition, we were unable to demonstrate any advantage of the low dose of exogenous 5-hydroxytryptamine and a severe disadvantage with the higher dose. Previous reports of transient increases in aggression in 5-hydroxytryptamine-treated subordinate lobsters did not take into account motor inhibition as a possible critical variable in aggression.

Anxiety-induced antinociception in mice: effects of systemic and intra-amygdala administration of 8-OH-DPAT and midazolam.

Mice exhibit antinociception after a single experience in the elevated plus maze (EPM), an animal model of anxiety. This study investigated the mechanisms involved in this form of anxiety-induced antinociception. Nociception was evaluated by means of the writhing test in mice confined either to the open or enclosed arms of the EPM. The effects of systemic (naloxone, midazolam and 8-OH-DPAT) or intra-amygdala (8-OH-DPAT, NAN-190 and midazolam) drug infusions were investigated in mice previously treated i.p. with 0.6% acetic acid, an algic stimulus that induces abdominal contortions. The effects of these drugs on conventional measures of anxiety (% entries and % time in open arms) in a standard EPM test were also independently investigated. Open-arm confinement resulted in a high-magnitude antinociception (minimum 85%, maximum 450%) compared with enclosed arm confinement. The opiate antagonist naloxone (1 mg/kg and 10 mg/kg) neither blocked this open arm-induced antinociception (OAIA) nor modified indices of anxiety in EPM. Administration of midazolam (0.5-2 mg/kg, s.c.) increased OAIA and produced antinociception in enclosed confined animals, as well as attenuating anxiety in the EPM. The 5-HT(1A) receptor agonist 8-OH-DPAT (0.05-1 mg/kg, s.c.) had biphasic effects on OAIA, antagonising the response at the lowest dose and intensifying it at the highest dose. In addition, low doses of this agent reduced anxiety in the EPM. Although bilateral injections of 8-OH-DPAT (5.6 nmol/0.4 microl) or NAN-190 (5.6 nmol and 10 nmol/0.4 microl) into the amygdala did not alter OAIA, increased anxiety was observed in the EPM. In contrast, intra-amygdala administration of midazolam (10 nmol and 30 nmol/0.4 microl) blocked both OAIA and anxiety. These results with systemic and intracerebral drug infusion suggest that 5-HT(1A) receptors localised in the amygdala are not involved in the pain inhibitory processes that are "recruited" during aversive situations. However, activation of these receptors does phasically increase anxiety. Although the intrinsic antinociceptive properties of systemically administered midazolam confounded interpretation of its effects on OAIA, intra-amygdala injections of this compound suggest that benzodiazepine receptors in this brain region modulate both the antinociceptive and behavioural (anxiety) responses to the EPM.

Inhibition of 11beta-hydroxysteroid dehydrogenase, the foeto-placental barrier to maternal glucocorticoids, permanently programs amygdala GR mRNA expression and anxiety-like behaviour in the offspring.

Glucocorticoids may underlie the association between prenatal stress, low birth weight and adult stress-associated disorders, e.g. hypertension and type 2 diabetes, increased hypothalamic-pituitary-adrenal (HPA) activity and affective dysfunction. Normally, 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD2) rapidly inactivates glucocorticoids in placenta and many foetal tissues, thus acting as a 'barrier' to maternal steroids. We investigated the effect of inhibiting foeto-placental 11beta-HSD in rats, using carbenoxolone (CBX), on subsequent HPA activity and regulation and stress-induced behaviour in adult offspring. Pregnant Wistar rats were injected with CBX (12.5 mg s.c.) or vehicle daily throughout pregnancy. CBX treatment reduced birth weight. Adult offspring of CBX-treated dams had persistently reduced body weight, increased basal corticosterone (CORT) levels, increased corticotropin-releasing hormone (CRH) and reduced glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus, though hippocampal GR and mineralocorticoid receptor (MR) mRNA expression were unaltered. In addition, these animals showed less grooming and rearing in an open field and reduced immobility in a forced swim test, and had increased GR mRNA expression in the basolateral (BLA), central (CEA) and medial (MEA) nuclei of the amygdala, with unaltered MR mRNA. These data suggest that disturbance of the foeto-placental enzymatic barrier to maternal glucocorticoids reduces birth and body weight, and produces permanent alterations of the HPA axis and anxiety-like behaviour in aversive situations. The behavioural and HPA effects may reflect GR gene programming in amygdala and hypothalamus, respectively. Foetal overexposure to endogenous glucocorticoids (prenatal stress or reduced activity of foeto-placental 11beta-HSD) may represent a common link between the prenatal environment, foetal growth and adult neuroendocrine and affective disorders.

Simulating Withdrawal Behaviors in Work Organizations: An Example of a Virtual Society

This article discusses computational modeling as a research discipline increasingly accessible to researchers in the social and behavioral sciences, a method necessary to allow us to address several important questions. Construction and use of virtual societies in which complex behavioral processes may be simulated in exquisite detail is possible because of the capacity and speed of desk top computers combined with requisite theoretical and methodological developments. Modeling has strengths orthogonal and complementary to those of the experimental tradition and correlational analyses of individual differences. These strengths can be exploited in many areas of psychology. Behavioral processes within a segment of a virtual society can be simulated with extreme levels of realism using overarching theoretical and empirical framework; segments can be combined to provide more macro statements. Variables that represent forces impinging on individuals from the macro-environment; variables that characterize relatively more micro-environments such as a work organization or the family or a classroom; and individual-level variables that summarize attitudinal, cognitive, and value states or traits can be included easily in simulations. Researchers can decompose and evaluate the interplay of multi-level causal forces as they interact within different theoretical models of how individuals enact different, interrelated behaviors. Temporal dynamics of behavioral processes, not well addressed by traditional research disciplines, can be exploited in modeling to permit the realistic study of dynamical, nonlinear systems. These points are illustrated by results from a program designed to simulate the process by which individuals withdraw from aversive work situations.

Maturational and gender differences in rodent escape strategies: Possible implications for preclinical models of anxiety

This study profiles two clearly dissociable escape strategies (jumping and backing off) in a newly established preclinical model of extreme anxiety (i.e., the unstable elevated plus maze) and examines the contribution of ontogeny and gender to the behavioral profiles exhibited. Clear age-related differences in escape behavior were found: Although the younger animals exhibited all the preparatory behaviors appropriate to flight from the apparatus—that is, attempting to back off, backtracking, preparing to jump, turning, and scanning—the older animals more readily translated these into actual escape. There were no significant sex-related differences in escape rates or in three of the escape-related behaviors— that is, backtracking, attempting to back off, and preparing to jump. Clear dissimilarities were, however, found in a number of other escape-linked behaviors: Females scanned, end-reached, and turned more than males. These results indicate that ontogeny and gender significantly contribute to the behaviors exhibited in aversive situations and might explain at least some of the inconsistent results frequently obtained in preclinical models of anxiety.

The Maternal Separation Paradigm and Adult Emotionality and Cognition in Male and Female Wistar Rats

A single 24-h maternal separation (MS) in the rat during the stress hyporesponsive period alters adult behavior and neuroendocrine stress response. The age of the animal at MS might be a crucial factor for effects in adulthood. We report here on adult behavioral effects of MS performed on postnatal day 4 (MS4), 9 (MS9), or 18 (MS18) in male and female Wistar rats. Unrelated subjects were used to avoid confounding litter effects. Subjects were tested on paradigms of unconditioned fear/anxiety, i.e., open field and elevated plus-maze, and on paradigms involving learning in an aversive situation, i.e., conditioned freezing, active avoidance, and water maze. In line with our predictions we obtained (a) sex differences that were consistent with enhanced fear/anxiety in males relative to females, (b) evidence that MS4 yielded deficits in active avoidance learning and conditioned freezing (trend level), whereas MS9 yielded enhanced active avoidance and water maze learning, (c) evidence (at trend level) that these effects of MS are greater in males than in females. There was no evidence for an effect of MS on paradigms of unconditioned fear/anxiety. We conclude that MS, irrespective of the age at separation, does not provide a robust environmental model of modified behavior in aversive situations.

The phenomenon of “one-trial tolerance” to the anxiolytic effect of chlordiazepoxide in the elevated plus-maze is abolished by the introduction of a motivational conflict situation

A single exposure to the elevated plus-maze test of anxiety reduces or abolishes the anxiolytic efficacy of benzodiazepines. The present study was designed to examine whether this phenomenon of “one-trial tolerance” resulted from a motivational deficit on trial 2. We hypothesized that whereas there is a motivational conflict on trial 1 in relation to the open arms (exploration drive X natural fear of open spaces), there is no “reason” for an animal to explore it on trial 2. A motivational conflict was introduced on trial 2 by rendering the enclosed arms of the apparatus aversive on trial 1. Thus, every time rats entered the enclosed arms, an aversive situation (light and hot air blow) was produced until they left the arm. On trial 2, rats did not receive this aversive stimulation. Chlordiazepoxide significantly enhaced the percent open arm time as well as the percent open arm entries on trial 2 in rats that had been submitted to the aversive stimulation in the enclosed arms on trial 1, but was not effective in rats which had been exposed to the apparatus in the absence of the aversive stimulation on trial 1. In addition, there was no difference in the percent open arm time and entries on trial 2 between saline-treated rats submitted to the aversive or non-aversive condition on trial 1. The aversive condition on trial 1 did not modify the number of total arm entries on trial 2, either. The results suggest that the anxiolytic effect of chlordiazepoxide in the elevated plus-maze depends on the presence of a motivational conflict situation.

Influence of male and female petters on plasma cortisol and behaviour: can human interaction reduce the stress of dogs in a public animal shelter?

During their second or third day in public animal shelter, juvenile/adult dogs were exposed to a venipuncture procedure. Then the dogs were either not petted or were petted in a prescribed manner by either a man or a woman; 20 min later, a second blood sample was collected. There was a clear increase in cortisol levels 20 min after the first venipuncture in juvenile/adult dogs that were not petted, but not in dogs that were petted by either a man or a woman. Additional comparisons showed that the petting procedure also inhibited the cortisol response following venipuncture in puppies. However, petting did not reduce the cortisol response to housing in the shelter per se. During petting, dogs made few attempts to escape, frequently were observed in a relaxed posture, and panting was common in juvenile/adult dogs. When dogs were petted immediately following removal from the living cage, those petted by women yawned more often and spent more time in a relaxed, head-up posture. Together, these results indicate that a previously observed sex difference in the effectiveness of petters in reducing the cortisol response was not due to some difference in odor or other nonbehavioural stimulus quality of men and women. Subtle aspects of petting technique appear to have pronounced effects on physiological and possibly behavioural responses of dogs confined in a shelter. Petting may be an effective means of reducing the cortisol responses of dogs to other common aversive situations, such as routine medical examinations and vaccination procedures at veterinary clinics as well as shelters.

The effect of some common management practices on the ease of handling of dairy cows

Cows which are fearful of humans can be difficult and, in some cases, dangerous to handle (Hemsworth et al., 1989; Boivin et al., 1992; De Passille et al., 1996). Since fear is evoked by painful or otherwise aversive situations, and since many procedures commonly utilized in a dairy barn can be assumed to be aversive, it is possible that these procedures affect handling ease. This hypothesis was tested using 40 multiparous and 40 primiparous dairy cows. Ease of handling was scored and then analysed for effects related to recent (6 months) management procedures. Ease of handling was determined in 5 tests: halter placement, leading, entering the squeeze, entering the headgate, and exiting the squeeze. The order of difficulty of these tests, as indicated by the herd average scores, was (1) exiting the squeeze, (2) entering the headgate, (3) halter placement, (4) entering the squeeze, and (5) leading. The scores for these tests were 1.5, 1.5, 2.1, 2.3 and 2.8, respectively, on a 5-point scale, where 1=easy to handle and 5=difficult to handle. Four categories of ease of handling were distinguished in the observed herd: (1) consistent ease (33%), (2) predominant ease (1 adverse response) (40%), (3) unpredictable (equal adverse and positive responses) (25%), and (4) consistent difficulty (1%). Although the ease of handling was relatively good in this herd, 24% of the cows were difficult to handle in more than one test. Ease of handling while being led was correlated with the score for squeeze entry ( r=0.23) and entering the squeeze and entering the headgate were also correlated ( r=0.47). Correlations between these variables were presumed to be related to previous hoof trimming in the squeeze. Both aversive experiences and inexperience in a squeeze were shown to negatively impact on the subsequent ease with which a cow could be led to the squeeze and confined in the headgate. However, squeeze experience was the only variable in which significant correlations were apparent. Aversive management procedures, applied only when necessary, and therefore on a random basis, did not appear to adversely affect the ease of handling of dairy cows in the squeeze or in the milking parlour.

Reversal of Learned Helplessness by Morphine in Rats: Involvement of a Dopamine Mediation

The aim of this study was to examine the role of dopamine neurotransmission in the effects of morphine in the learned helplessness paradigm in rats, a generally recognized model of depression. In this model, rats first exposed to inescapable shocks (stressed rats) exhibited an escape deficit in a subsequent shuttle-box test performed 48 h later for 3 consecutive days. The numbers of escape failures and intertrial crossings (motor activity during each intertrial interval) were recorded. Morphine was injected twice daily for 5 days (6 mg/kg/day, SC), and haloperidol, a preferential D 2-dopamine receptor antagonist, was injected IP 15 min before each shuttle-box session. At the highest dose tested (150 μg/kg) haloperidol mimicked the behavioral deficit produced by inescapable shocks. A 37.5 μg/kg dose of haloperidol, which was ineffective by itself, reversed the morphine-induced improvement of escape behavior in previously stressed rats and the morphine-induced increase in intertrial activity in both stressed and nonstressed animals. These results support roles (a) for a dysregulation of dopaminergic neuronal activity in the expression of escape deficit subsequent to an inescapable aversive situation, and (b) for a dopaminergic mediation in the effects of morphine in the learned helplessness paradigm.

Influences of the bed nucleus of the stria terminalis and of the paraventricular nucleus of the hypothalamus on the excitability of hippocampal-lateral septal synapses in mice

Previous experiments have shown that conditioning in aversive situations is associated with specific changes in excitability of hippocampal-septal synaptic transmission and that these changes might be related to a modulation of this synaptic transmission by afferents originating from the bed nucleus of the stria terminalis (BNST) and from the paraventricular nucleus (PVN) of the hypothalamus. Accordingly, the aim of the present experiment was to assess changes in excitability of hippocampal-septal synapses by varying the interval between the application of a conditioning pulse in either the BNST or the PVN, and a test pulse in fimbria fibers (FF). Electrical stimulation of FF, induces in the lateral septum (LS) a field potential characterized by two negative waves (N2 and N3) the magnitude of which is an index of excitability of two populations of target cells located in the ventral and dorsal lateral septum, respectively. Results showed that prestimulation of both the BNST and the PVN produced an increase in the amplitude of the N3 wave, although the optimal interpulse interval required for producing maximal increase was different as a function of the two structures. Only prestimulation of the BNST induced a significant increase in the amplitude of the N2 wave. These results suggest that the PVN projects mainly to the dorsal aspect of the LS, while the BNST projects to both dorsal and ventral parts of the LS. Together with results from previous experiments conducted in behaving mice exposed to conditioned aversive stimuli, it is concluded that these projections might play a role in the relief of contextual conditioned fear.