Decreased reactivity to anxiolytics caused by early protein malnutrition in rats

Rotated nursing environment with underfeeding: A form of early-life adversity with sex- and age-dependent effects on coping behavior and hippocampal neurogenesis

We investigated how a unique form of early-life adversity (ELA), caused by rotated nursing environment to induce underfeeding, alters anxiety-like and stress-coping behaviors in male and female Sprague Dawley rats in adolescence and adulthood. Adult female rats underwent either thelectomy (thel; surgical removal of teats), sham surgery, or no surgery (control) before mating. Following parturition, litters were rotated between sham and thel rats every 12 h to generate a group of rats that experienced ELA (rotated housing, rotated mother, and 50% food restriction) from postnatal day 0 to 26. Control litters remained with their natal, nursing dams. Regardless of age and sex, ELA reduced activity in the periphery of the open field. ELA increased immobility in the forced swim test, particularly in adults. We used doublecortin immunohistochemistry to identify immature neurons in the hippocampus. ELA increased the number and density of immature neurons in the dentate gyrus of adolescent males (but not females) and reduced the density of immature neurons in adult males (but not females). This research indicates that a unique form of ELA alters stress-related passive coping and hippocampal neurogenesis in an age- and sex-dependent manner.

Spatial Learning Deficits Induced by Muscimol and CL218,872: Lack of Effect of Prenatal Malnutrition

The sensitivity of prenatal protein malnourished rats to the amnestic properties of the direct GABAA receptor agonist muscimol and the selective benzodiazepine (BZ) receptor agonist, CL218,872, was studied in the male offspring of rats provided with a protein deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy. At postnatal day 90, rats were tested during acquisition of the submerged platform version of the Morris water maze task using four systemic doses of muscimol (0.1, 0.3, 1.0 and 1.8 mg/kg i.p.) or three systemic doses of CL218,872 (1.0, 3.2, and 5.6 mg/kg i.p.). In a dose dependent manner both drugs impaired acquisition of the task and impaired accuracy of the search pattern on the probe trial (platform removed). However, neither drug dissociated the performance of the two nutritional groups. These data are important in light of previous findings of differential behavioral effects of the non-specific BZ agonist, chlordiazepoxide (CDP), on spatial learning and on drug discrimination in prenatally malnourished rats and in the context of previous findings of reduced sensitivity to the anxiolytic effects of non-specific BZ receptor agonists across a wide variety of models of malnutrition. The present findings also support the concept that prenatal malnutrition does not affect the global functioning of the GABAA receptor, but fundamentally alters the way in which a subset of GABAA receptors (i.e. those containing the alpha2, alpha3 and/or the alpha5 but not the alpha1 subunit) is modulated by BZs.

Early postnatal protein-calorie malnutrition and cognition: a review of human and animal studies

Malnutrition continues to be recognized as the most common and serious form of children's dietary disease in the developing countries and is one of the principal factors affecting brain development. The purpose of this paper is to review human and animal studies relating malnutrition to cognitive development, focusing in correlational and interventional data, and to provide a discussion of possible mechanisms by which malnutrition affects cognition.

Differential response to gepirone but not to chlordiazepoxide in malnourished rats subjected to learned helplessness

The learned helplessness (LH) paradigm is characterized by learning deficits resulting from inescapable events. The aims of the present study were to determine if protein-calorie malnutrition (PCM) alters learning deficits induced by LH and if the neurochemical changes induced by malnutrition alter the reactivity to treatment with GABA-ergic and serotonergic drugs during LH. Well-nourished (W) and PCM Wistar rats (61 days old) were exposed or not to inescapable shocks (IS) and treated with gepirone (GEP, 0.0-7.5 mg/kg, intraperitoneally, N = 128) or chlordiazepoxide (0.0-7.5 mg/kg, intraperitoneally, N = 128) 72 h later, 30 min before the test session (30 trials of escape learning). The results showed that rats exposed to IS had higher escape latency than non-exposed rats (12.6 +/- 2.2 vs 4.4 +/- 0.8 s) and that malnutrition increased learning impairment produced by LH. GEP increased the escape latency of W animals exposed or non-exposed to IS, but did not affect the response of PCM animals, while chlordiazepoxide reduced the escape deficit of both W and PCM rats. The data suggest that PCM animals were more sensitive to the impairment produced by LH and that PCM led to neurochemical changes in the serotonergic system, resulting in hyporeactivity to the anxiogenic effects of GEP in the LH paradigm.

A panic experimental model: Validation of a complex operant behavioral method in undernourished rats, with desipramine to provide a template effect profile

INTRODUCTION

Clinical studies have shown that some antidepressants may be more efficient than benzodiazepines to alleviate anxiety associated with panic disorders; however, operant conflict procedures in rats developed so far seem not particularly able to model human anxiety sensitive to antidepressant treatments. Previous panic models with learned responses did not statistically subtract the effect of confounding factors from the variable of interest.

METHODS

Undernourished rats were selected due to their behavioral and neurobiological resemblance to human patients suffering from panic disorder. The Geller-Seifter paradigm represented the stressful environmental condition in adult life. Desipramine (10 mg/kg/day) or saline were administered IP during 7 days under a cross over design (N=10). Five daily 15 min-operant sessions were carried out on each experiment. Unpunished, unrewarded and punished operant behavioral periods were identical both in their duration and in their reward system (the FR1 schedule) in order to measure response suppression, which has not been considered in previous studies with the Geller-Seifter paradigm. The dependent variable was the difference between comparable unpunished and punished periods.

RESULTS

A significant Diet x Drug interaction was observed in the dependent variable, which represented the level of "suppression/suppression release" induced by treatments.

DISCUSSION

Compared to control rats, deprived rats showed a significant and selective anticonflict effect of desipramine on the stressful and complex operant performance. The animal model of perinatally protein-deprived rats along with the Geller-Seifter's operant behavioral paradigm may represent a more sensitive approach to model human anxiety sensitive to antidepressant treatments by considering the combined impact of both early biological trauma and adult learned experiences under the same design.

Prenatal protein malnutrition enhances stimulus control by CDP, but not a CDP/THIP combination in rats

In the present study, the effects of prenatal protein malnutrition on stimulus control exerted by the benzodiazepine (BZ), chlordiazepoxide (CDP) and the GABA-A receptor agonist 4,5,6,7-tetrahydroisoxazolo[5,4-c]pyridin-3-ol (THIP) were characterized. The adult, male offspring of female Sprague-Dawley rats fed either low (6% casein) or adequate (25% casein) protein diets 5 weeks prior to mating and throughout pregnancy served as subjects. Subjects were first trained to discriminate CDP (8.0 mg/kg ip) from saline using drug discrimination procedures. Once a criterion level of performance was achieved, generalization tests were performed to lower doses of CDP (4.0, 2.0, 1.0, 0.5 and 0.25 mg/kg) and then to several doses of THIP (10.0, 7.5, 5.6 and 3.2 mg/kg). Lastly, the ability of a single dose of THIP (3.0 mg/kg) to enhance discriminative control by several low doses of CDP (4.0, 2.0, 1.0 and 0.5 mg/kg) was assessed. Although both diet groups acquired the original CDP/saline discrimination at the same rate, malnourished rats exhibited significantly more generalization to low doses of CDP than their well-nourished counterparts. Neither diet group exhibited significant generalization to THIP nor a difference in THIP's ability to enhance the CDP cue. These results suggest that a subject's sensitivity to the stimulus properties of drugs can be selectively modified by prenatal malnutrition.

Prenatally protein-malnourished rats are less sensitive to the amnestic effects of medial septal infusions of chlordiazepoxide

Evidence is mounting that prenatal protein malnutrition affects the physiological properties of the GABAergic neurotransmitter system in rats. To investigate the functional behavioral consequences of these changes, chlordiazepoxide (CDP, a positive modulator of the GABA(A) receptor) was applied directly to the medial septum and the amnestic response appraised. In adulthood, male offspring of rats provided with a protein-deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy underwent stereotaxic surgery to implant steel cannulae aimed at the medial septum. After recovery, spatial learning performance in the submerged platform version of the Morris water maze task was assessed immediately following a 1 microl infusion of either artificial cerebrospinal fluid (aCSF), or one of three doses of CDP (15, 30 and 60 nmol). Well-nourished control rats demonstrated a robust amnestic response to intraseptal CDP. During task acquisition, well-nourished rats administered each of the doses exhibited significantly longer escape latencies than those given aCSF. On the probe trial (platform removed) a lower proportion of time was spent in the target quadrant (all three doses) at a greater average distance from the former platform location (30 and 60 nmol doses). In contrast, prenatally malnourished rats exhibited a muted sensitivity to CDP, most notable at the 30 nmol dose. These findings provide further support for functional changes within the GABAergic system consequent to malnutrition.

Chlordiazepoxide-induced spatial learning deficits: dose-dependent differences following prenatal malnutrition

The sensitivity of prenatally protein-malnourished rats to the amnestic properties of the benzodiazepine (BZ) receptor agonist, chlordiazepoxide (CDP), was studied in the male offspring of rats provided with a protein-deficient diet (6% casein) for 5 weeks prior to mating and throughout pregnancy. Rats were tested during acquisition of the submerged platform version of the Morris water maze task using three systemic doses of CDP (3.2, 5.6, and 7.5 mg/kg i.p.) at two ages (day 30 and day 90). At 30 days, prenatally malnourished rats showed less sensitivity to the amnestic effect of the 5.6-mg/kg dose when compared with well-nourished controls by displaying shorter swim paths during acquisition and a more selective search of the target quadrant upon removal of the platform (probe trial). At 90 days, prenatally malnourished rats again showed less sensitivity to CDP at a dose of 5.6 mg/kg, but more sensitivity to the 3.2-mg/kg dose (indicated on the probe trial). No obvious relationship was identified between the nutritional group differences in behavioral sensitivity to CDP at 90 days and their BZ receptor density in the hippocampus or medial septum. It can be concluded that prenatal malnutrition alters the amnestic response to CDP in a dose-dependent and developmentally specific manner, thus providing further support for functional changes within the GABAergic system subsequent to malnutrition.

Lack of tolerance to the anxiolytic effect of diazepam and pentobarbital following chronic administration in perinatally undernourished rats

Adult female rats, undernourished at perinatal age, were evaluated for anxiolytic action in the plus-maze test after acute and chronic administration of diazepam (DZP) and pentobarbital (PTB). Deprived (D) rats chronically treated with vehicle showed an increased anxiety as compared with control (C) animals. A single intraperitoneal (i.p.) administration of DZP (1 mg/kg) or PTB (7.5 mg/kg) produced similar anticonflict effect in both C and D rats. Tolerance to the anxiolytic effect of DZP and PBT developed in C rats after a 15-day administration schedule, whereas no tolerance was observed in D animals. Drug disposition was not altered after chronic treatment either in C or in D rats. Gamma-aminobutyric acid (GABA)-mediated chloride uptake in microsacs of cerebral cortex of naive D rats was decreased as compared with naive C rats. After chronic DZP administration (1 mg/kg/day i.p. for 15 days), GABA-mediated 36Cl- influx in brain cortex microsacs of C rats did not change; however, GABA efficacy was increased in microsacs of D animals. In addition, chronic DZP treatment induced GABA-benzodiazepine uncoupling in brain cortex of C rats, but not in D animals, as assessed by chloride uptake in microsacs. Chronic PTB treatment (7.5 or 30 mg/kg/day i.p. for 15 days) did not modify GABA stimulation or GABA-PTB interaction in cortical microsacs of C or D rats.

Response threshold to aversive stimuli in stimulated early protein-malnourished rats

Two animal models of pain were used to study the effects of short-term protein malnutrition and environmental stimulation on the response threshold to aversive stimuli. Eighty male Wistar rats were used. Half of the pups were submitted to malnutrition by feeding their mothers a 6% protein diet from 0 to 21 days of age while the mothers of the other half (controls) were well nourished, receiving 16% protein. From 22 to 70 days all rats were fed commercial lab chow. Half of the animals in the malnourished and control groups were maintained under stimulating conditions, including a 3-min daily handling from 0 to 70 days and an enriched living cage after weaning. The other half was reared in a standard living cage. At 70 days, independent groups of rats were exposed to the shock threshold or to the tail-flick test. The results showed lower body and brain weights in malnourished rats when compared with controls at weaning and testing. In the shock threshold test the malnourished animals were more sensitive to electric shock and environmental stimulation increased the shock threshold. No differences due to diet or environmental stimulation were found in the tail-flick procedure. These results demonstrate that protein malnutrition imposed only during the lactation period is efficient in inducing hyperreactivity to electric shock and that environmental stimulation attenuates the differences in shock threshold produced by protein malnutrition.

Malnutrition and reactivity to drugs acting in the central nervous system

There is a well-established body of data demonstrating that protein or protein-calorie malnutrition experienced early in life is associated with neuroanatomical, neurochemical, as well as behavioral alterations in both animals and humans. A number of studies has focused on the following question: are the neuroanatomical and/or neurochemical changes produced by early malnutrition responsible for the altered behaviors reported in malnourished animals? A tool that has been used to help answer this question is the administration of drugs with specific actions in the various neurotransmitter systems in the central nervous system (CNS). This neuropharmacological approach has produced a considerable amount of data demonstrating that malnourished animals react to drugs differently from controls, suggesting that the altered behavioral expression of these animals could be partly explained by the alterations in the brain function following malnutrition. The present review will provide an overview of the literature investigating the reactivity of malnourished animals to psychoactive drugs acting through GABAergic, catecholaminergic, serotonergic, opioid and cholinergic neurotransmitter systems. Altered responsiveness to psychoactive drugs in malnourished animals may be especially relevant to understanding the consequences of malnutrition in human populations.

5-Hydroxytryptamine pathways in anxiety and its treatment

The effects of manipulating 5-hydroxytryptamine (5HT) neuronal function in humans and in animals are reviewed. 5HT pathways do not have a unitary function in modulating anxiety. It is proposed that, rather than acting as input or output channels for brain aversive systems, these pathways provide information concerning waking/motor status, which is crucial to the organisation of appropriate responses to threat. Each terminal region can make use of this information in different ways. Globally, the influence of 5HT neurones on higher centres appears predominantly to facilitate information processing relevant to threat, while their major influence on brainstem centres may be a restraining one.

Effects of ethanol, caffeine, and clorazepate on hypertonic NaCl solution intake in rats

Previous reports indicate that several anxiolytics enhance the intake of hypertonic saline in rehydrating rats. This experiment was conducted to determine the effects of repeated (5 sessions) injection (i.p.) of ethanol (0.4 or 0.8 g/kg), caffeine (20 or 40 mg/kg) or clorazepate (3 mg/kg) on the ingestion of hypertonic saline (1.8%) in water-deprived rats. Saline intake increased with the acute administration of both clorazepate and ethanol (two doses), but it decreased with caffeine (two doses). It seems that the increase or decrease of hypertonic saline ingestion following acute drug administration continues to correlate well with anxiolytic or anxiogenic actions. However, following repeated administration of caffeine and ethanol, the effects on saline intake were not maintained in a reliable manner.

Effects of early protein malnutrition and environmental stimulation upon the reactivity to diazepam in two animal models of anxiety

In order to investigate the effects of early protein malnutrition and environmental stimulation upon the response to the anxiolytic properties of diazepam, two animal models of anxiety (elevated plus-maze and light-dark transition tests) were used. Rats were malnourished by feeding their dams a 6% protein diet during the lactation period (0-21 days of age) while well-nourished controls received a 16% protein diet. From 21 to 70 days of age all rats received a balanced lab chow diet. Environmental stimulation consisted of 3-min daily handling from birth to 70 days of age. Additional stimulation was provided from 21 to 70 days of age by rearing the rats in an enriched living cage. Eight groups of rats were studied in a 2 (malnourished or well-nourished) x 2 (stimulated or nonstimulated) x 2 (diazepam or vehicle) design. At 70 days of age, independent groups of rats treated with diazepam (2.5 mg/kg, IP) or vehicle were submitted to testing in the elevated plus-maze or light-dark transition procedures. The results showed that both diazepam and environmental stimulation reduced anxiety in the elevated plus-maze; stimulation changed the anxiolytic response to diazepam and the two diet conditions altered differentially the response to both pharmacological and stimulation procedures. These results suggest that environmental stimulation can affect differentially the behavioral response of malnourished and well-nourished rats treated with diazepam.

Multiple serotonin mechanisms in animal models of anxiety: environmental, emotional and cognitive factors

Responses to serotonergic drugs in animal models of 'anxiety' are reviewed with emphasis on the elevated X-maze. Evidence for the 'classic' hypothesis, that decreasing serotonergic function is anxiolytic and increasing it anxiogenic, is most consistent in models of behavioural inhibition where the stimulus inhibits an approach response (conflict models). However, paradoxical drug effects are also frequent, especially where the aversive stimulus evokes an active response. Both types of drug effect are equally frequent in the elevated X-maze. 'Anxiety' models may detect multiple sites and mechanisms of action of the same drug; this may indicate multiple anxiety-related neurological mechanisms in the brain. However, not all drug effects in 'anxiety' models are necessarily related to anxiety itself. It is possible that cognitive factors may affect stimulus evaluation, and response inhibition by an aversive stimulus may be a special case of a wider role for serotonin in behavioural control. Clinical implications of these observations are considered.

Perinatally protein-deprived rats and reactivity to anxiolytic drugs in the plus-maze test: an animal model for screening antipanic agents?

Adult rats submitted to a protein deprivation schedule at perinatal age (from 14th day of fetal life until 50 days of age) and then recovered on balanced chow (D rats) were assayed in the elevated plus-maze test for anticonflict effects of diazepam and drugs with therapeutic efficacy in panic disorders as compared with controls (C rats). Diazepam and alprazolam showed a similar anticonflict effect in D rats than in C rats. In contrast, buspirone, which was ineffective in C rats at a wide dosage range, showed a significant anticonflict effect on D rats at 0.3 mg/kg. Neither propranolol, desipramine, nor phenelzine treatment (10 mg/kg/day during 3-7 days) induced anticonflict effect in C rats. Conversely, these treatments fostered a significant and selective anxiolytic effect on D rats. Such results underscore long-lasting alterations caused by early undernutrition, namely, changes in reactivity to the drugs assayed. In addition, perinatally deprived rats may represent a useful animal model for studying potential antipanic agents.

An assessment of the elevated X-maze for studying anxiety and anxiety-modulating drugs

The elevated X-maze has strong claims to validity as an animal model of anxiety, both in theoretical basis and drug responses. The model is sensitive to actual and putative anxiolytics, but because insufficient time has elapsed since its discovery, no agent first predicted to be anxiolytic in the elevated X-maze has been brought into general use yet. It has an advantage in detecting anxiolytic and anxiogenic agents under the same operating conditions. The design and execution of experiments with the model is discussed and it is shown that baseline arm preference and the size or direction of drug effects differ in the procedural factors affecting them. Because it presents features of both passive and active avoidance and approach/avoidance conflict, it may prove able to detect drug effects in different forms of human anxiety and aid in understanding their neurobiology.

Prenatal malnutrition and development of the brain

In this review, we have summarized various aspects as to how prenatal protein malnutrition affects development of the brain and have attempted to integrate several broad principles, concepts, and trends in this field in relation to our findings and other studies of malnutrition insults. Nutrition is probably the single greatest environmental influence both on the fetus and neonate, and plays a necessary role in the maturation and functional development of the central nervous system. Prenatal protein malnutrition adversely affects the developing brain in numerous ways, depending largely on its timing in relation to various developmental events in the brain and, to a lesser extent, on the type and severity of the deprivation. Many of the effects of prenatal malnutrition are permanent, though some degree of amelioration may be produced by exposure to stimulating and enriched environments. Malnutrition exerts its effects during development, not only during the so-called brain growth spurt period, but also during early organizational processes such as neurogenesis, cell migration, and differentiation. Malnutrition results in a variety of minimal brain dysfunction-type syndromes and ultimately affects attentional processes and interactions of the organism with the environment, in particular producing functional isolation from the environment, often leading to various types of learning disabilities. In malnutrition insult, we are dealing with a distributed, not focal, brain pathology and various developmental failures. Quantitative assessments show distorted relations between neurons and glia, poor formation of neuronal circuits and alterations of normal regressive events, including cell death and axonal and dendritic pruning, resulting in modified patterns of brain organization. Malnutrition insult results in deviations in normal age-related sequences of brain maturation, particularly affecting coordinated development of various cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter cell types and, ultimately, affecting the formation of neuronal circuits and the commencing of activity of neurotransmitter systems. It is obvious that such diffuse type "lesions" can be adequately assessed only by interdisciplinary studies across a broad range of approaches, including morphological, biochemical, neurophysiological, and behavioral analyses.

5HT drugs in animal models of anxiety

It has been widely accepted that 5HT neurones promote anxiety, in humans as well as in animal models. This could be termed the "classic" hypothesis and it has led to a determined search for drugs which reduce 5HT function, especially agents which have selective actions at 5HT receptor subtypes. However, these novel agents tend to have weak and/or variable effects in animal models and more detailed examination of their actions suggests that not all findings are accounted for by the classic hypothesis. There appear to be circumstances in which increased 5HT activity can reduce anxious behaviour. There is increasing evidence for multiple anxiety mechanisms, which may be able to explain differential patterns of drug effects within and between models. Animal models of anxiety may also detect non-anxiety factors: effects on cognition or on impulsivity could be reflected in some models. This could be important in the light of recent evidence that 5HT-selective reuptake inhibitors are effective in impulsivity disorders. The classic hypothesis of 5HT function in anxiety may be only one part of an increasingly complex story. Unravelling the rest of this story is likely to lead to new insights in our understanding of anxiety and related disorders.

Effects of early postnatal malnutrition and chlordiazepoxide on experimental aversive situations

In order to study the lasting consequences of brain changes caused by early malnutrition, rats were fed a protein-deficient diet from birth until 49 days of age and a balanced diet from day 50 to day 70. At 49 and 70 days of age, independent groups of animals were tested in the locomotor activity, step-down inhibitory avoidance, and flinch-jump nociceptive tests. Also, at 49 days of age, malnourished and control rats were sacrificed in order to evaluate the weight of brain regions. Malnourished rats had lower body and brain weights (telencephalon and brain stem) than control rats. Malnourished rats also showed less locomotor activity at the beginning of the test session, lower flinch and jump thresholds, and longer step-down latencies than control animals. Chlordiazepoxide (5 mg/kg, IP) shortened step-down latency of well-nourished rats, but was ineffective in malnourished rats. These and previously reported results indicate that early protein malnutrition causes long-lasting impairment of neuronal systems underlying emotional behavior.

Neonatal administration of a GABA-T inhibitor alters central GABAA receptor mechanisms and alcohol drinking in adult rats

Long-term effects of chronic treatment with a GABA-T (GABA-transaminase) inhibitor, ethanolamine O-sulphate (EOS) (200 mg/kg/day for the postnatal days 3-21) on the binding parameters of GABAA receptors, hypothalamic monoamines and subsequent behavior were studied in Wistar rats. At the age of 1 month, EOS-treated rats showed reduced activity in the open-field and, at the age of 4 months, their voluntary alcohol consumption was increased. No changes were seen in Porsolt's swim test or in the plus-maze test. Weight gain was significantly retarded in EOS-treated rats. Maximal stimulation of [3H] flunitrazepam binding by GABA was decreased in the cerebral cortex and the EC50-value for the GABA stimulation increased in the hippocampus in the EOS rats at the age of 4 months. EOS treatment did not alter the cerebellar diazepam sensitive and insensitive binding components of the imidazobenzodiazepine [3H]Ro 15-4513. No changes were observed in the hypothalamic monoamine concentrations. The results are in agreement with the idea that GABA-T inhibitor treatment permanently alters GABAA mechanisms. Moreover, altering the CNS GABA level during development increases adult alcohol intake in rat.

Early life protein malnutrition changes exploration of the elevated plus-maze and reactivity to anxiolytics

In order to investigate whether protein malnutrition in early life causes lasting changes in reactivity to anxiolytic drugs, exploration of the elevated plus-maze was used. Rat dams during lactation (21 days) and pups after weaning until day 49 of life were fed on 8% casein diet (M rats), while their well-nourished controls received 25% casein (W rats). From day 50 on all animals ate the same balanced diet. Experiments started on day 70. Under the non-drug condition, M rats tended to explore the open arms of the maze relatively more than W rats. Diazepam (0.5-5 mg/kg, IP) dose-dependently increased the percentage of open/total arm entries without significantly affecting the total number of arm entries in W rats. This selective anxiolytic effect of diazepam was considerably smaller in M rats. Ipsapirone (0.5-5 mg/kg) caused a similar though less pronounced anxiolytic effect in W rats, whereas the drug decreased both the % open/total and total arm entries in M rats. In contrast, ritanserin (0.05-1 mg/kg) significantly increased the % open/total arm entries in M rats only, though not in a dose-dependent way. Isamoltane (2.5-20 mg/kg) was ineffective on both M and W rats. These results indicate that early protein malnutrition causes long-lasting alterations in brain systems regulating emotional behaviour.