Showing papers in "Pharmacology, Biochemistry and Behavior in 1996"

A review of the validity and variability of the elevated plus-maze as an animal model of anxiety.

Abstract: Despite or possibly by virtue of the fact that it is one of the most commonly used animal models of anxiety the Elevated Plus-Maze (EPM) results in a wide range of, often contradictory, results following pharmacological experiments. The responses from a questionnaire distributed to 65 groups that have published studies using the EPM in the past 3 years has, along with reference to published reports, enabled some conclusions regarding the influencing factors to be drawn. Some evidence for differential sensitivities between strains exists, with albino rats being more sensitive to the anxiolytic effects of 5-HT3 receptor antagonists and 5-HT1A receptor agonists than pigmented animals. Most important, however, is the manipulation of the animals prior to testing and the aversiveness of the test conditions themselves. Stressing animals before testing (e.g., by moving from holding to test room) or using more aversive test conditions (e.g., elevated light levels) increases sensitivity to potential anxiolytics. Animals that are habituated to gentle handling or tested in less aversive conditions (e.g., EPM with ledges) show reduced likelihood of anxiolytic responses with administration of 5-HT3 antagonists, 5-HT1A agonists, and benzodiazepines.

Role of 5-HT in stress, anxiety, and depression

Abstract: There are conflicting results on the function of 5-HT in anxiety and depression. To reconcile this evidence, Deakin and Graeff have suggested that the ascending 5-HT pathway that originates in the dorsal raphe nucleus (DRN) and innervates the amygdala and frontal cortex facilitates conditioned fear, while the DRN-periventricular pathway innervating the periventricular and periaqueductal gray matter inhibits inborn fight/flight reactions to impending danger, pain, or asphyxia. To study the role of the DRN 5-HT system in anxiety, we microinjected 8-OH-DPAT into the DRN to inhibit 5-HT release. This treatment impaired inhibitory avoidance (conditioned fear) without affecting one-way escape (unconditioned fear) in the elevated T-maze, a new animal model of anxiety. We also applied three drug treatments that increase 5-HT release from DRN terminals: 1) intra-DRN microinjection of the benzodiazepine inverse agonist FG 4172, 2) intra-DRN microinjection of the excitatory amino acid kainic acid, and 3) intraperitoneal injection of the 5-HT releaser and uptake blocker D-fenfluramine. All treatments enhanced inhibitory avoidance in T-maze. D-Fenfluramine and intra-DRN kainate also decreased one-way escape. In healthy volunteers, D-fenfluramine and the 5-HT agonist mCPP (mainly 5-HT2C) increased, while the antagonists ritanserin (5-HT2A/2C) and SR 46349B (5-HT2A) decreased skin conductance responses to an aversively conditioned stimulus (tone). In addition, D-fenfluramine decreased, whereas ritanserin increased subjective anxiety induced by simulated public speaking, thought to represent unconditioned anxiety. Overall, these results are compatible with the above hypothesis. Deakin and Graeff have suggested that the pathway connecting the median raphe nucleus (MRN) to the dorsal hippocampus promotes resistance to chronic, unavoidable stress. In the present study, we found that 24 h after electrolytic lesion of the rat MRN glandular gastric ulcers occurred, and the immune response to the mitogen concanavalin A was depressed. Seven days after the same lesion, the ulcerogenic effect of restraint was enhanced. Microinjection of 8-OH-DPAT, the nonselective agonist 5-MeO-DMT, or the 5-HT uptake inhibitor zimelidine into the dorsal hippocampus immediately after 2 h of restraint reversed the deficits of open arm exploration in the elevated plus-maze, measured 24 h after restraint. The effect of the two last drugs was antagonized by WAY-100135, a selective 5-HT1A receptor antagonist. These results are compatible with the hypothesis that the MRN-dorsal hippocampus 5-HT system attenuates stress by facilitation of hippocampal 5-HT1A-mediated neurotransmission. Clinical implications of these results are discussed, especially with regard to panic disorder and depression.

The Influence of Open Arm Ledges and Maze Experience in the Elevated Plus-Maze

Abstract: In Experiment 1, rats were tested in a plus-maze, with or without small ledges on the open arms, after injection with vehicle or chlordiazepoxide (7.5 mg/kg). They were scored either on their first or second exposure to the maze; those scored on trail 2 had received a 5-min undrugged exposure to the maze 24 h earlier. This dose of chlordiazepoxide had a significant anxiolytic effect on trial 1 only in the maze without ledges, and on trial 2 only in the maze with ledges; thus, the presence of ledges differentially affected anxiolytic sensitivity on trials 1 and 2. The results of a factor analysis study (Experiment 2) confirmed that ledges had a differential effect when rats were repeatedly exposed to the maze. Thus, in the maze without ledges, the scores reflecting anxiolytic activity on trial 1 loaded on one factor, whereas the scores from trials 2 and 3 loaded on another independent factor. In the maze with ledges, the scores reflecting anxiolytic activity on trials 1, 2, and 3 loaded on three independent factors. Considering the published evidence and the results of the present study, we suggest that both types of plus-maze may be measuring the same type of anxiety with different sensitivities on trial 1 (e.g., generalised anxiety or fear of open spaces); different types of anxiety on trial 2 (without ledges--phobia/fear of heights; with ledges--not known), and trial 3 in the maze with ledges, yet another type of anxiety. The factor analysis results are also presented for ethological measures on the plus-maze, and for activity and exploration in the holeboard. Based on the factor loadings, a composite measure of anxiety on trial 1 is presented which will increase the sensitivity of the plus-maze to anxiolytic treatments. The measures of motor activity in the plus-maze load on a different factor from those derived from the holeboard, thus cautioning against considering all measures of motor activity as interchangeable.

Mesolimbic dopaminergic system activity as a function of food reward: A microdialysis study

Abstract: The mesolimbic dopaminergic system (MDS) has been shown to be implicated in feeding behaviors. The present experiment was conducted to examine the effects of the sensory properties of food ingested on MDS activity. Microdialysis coupled to high-performance liquid chromatography with electrochemical detection was employed to measure the extracellular levels of dopamine (DA) and its main metabolites (DOPAC and HVA) in the nucleus accumbens of freely moving rats. During microdialysis sessions rats had access or not to powdered foods varying in palatability: short cakes as highly palatable (HP) food and regular chow as low palatable (LP) food. In the absence of food, there were no alterations in extracellular levels of DA, DOPAC, and HVA. During feeding, DA rose significantly with a greater rise for the HP than the LP food. Levels of DOPAC and HVA only reached significance with the HP food. The results indicate that the MDS is activated on ingestion of food, and suggest that MDS activity is related to the rewarding properties of foods.

Aniracetam restores object recognition impaired by age, scopolamine, and nucleus basalis lesions.

Abstract: Object recognition was investigated in adult and aging male rats in a two-trials, unrewarded, test that assessed a form of working-episodic memory. Exploration time in the first trial, in which two copies of the same object were presented, was recorded. In the second trial, in which one of the familiar objects and a new object were presented, the time spent exploring the two objects was separately recorded and a discrimination index was calculated. Adult rats explored the new object longer than the familiar object when the intertrial time ranged from 1 to 60 min. Rats older than 20 months of age did not discriminate between familiar and new objects. Object discrimination was lost in adult rats after scopolamine (0.2 mg/kg SC) administration and with lesions of the nucleus basalis, resulting in a 40% decrease in cortical ChAT activity. Both aniracetam (25, 50, 100 mg/kg os) and oxiracetam (50 mg/kg os) restored object recognition in aging rats, in rats treated with scopolamine, and with lesions of the nucleus basalis. In the rat, object discrimination appears to depend on the integrity of the cholinergic system, and nootropic drugs can correct its disruption.

Aversive effects of the synthetic cannabinoid CP 55,940 in rats

Abstract: A series of experiments investigated the behavioral and hedonic effects of the synthetic cannabinoid CP 55,940 in male Wistar rats. CP 55,940 had a biphasic effect on locomotor activity, with a 10 μg/kg dose causing locomotor stimulation and a 100 μg/kg dose causing profound hypoactivity. CP 55,940 (100 μg/kg) also caused a marked hypothermia for at least 3 h following administration, while lower doses (2.5 and 10 μg/kg) had no effect. CP 55,940 (100 gmg/kg) had anorexic and hyperdipsic effects for up to 24 h following administration and caused significant reductions in body weight. CP 55,940 (100 μg/kg) also caused significant avoidance to a flavoured fluid (saccharin) with which it was paired. In the conditioned place preference paradigm both the 10 μg/kg and 100 μg/kg doses of CP 55,940 produced significant place avoidance. It is concluded that CP 55,940 is aversive to rats. The possible mechanisms underlying this aversion are discussed.

Psychosocial stress in tree shrews: Clomipramine counteracts behavioral and endocrine changes

Abstract: Male tree shrews (Tupaia belangeri) provide an animal model to study the neurobehavioral consequences of chronic psychosocial stress When living in visual and olfactory contact with a male conspecific by which it has been defeated, the subordinate tree shrew shows dramatic behavioral, physiological, and neuroendocrine changes Because the over all pattern of these changes resemble a depression-like symptomatology, we investigated to what extent the behavioral and endocrine changes in subordiante animals can be reversed by treatment with the tricyclic antidepressant clomipramine In the present study, animals were subjected to a 10-day period of psychosocial conflict to elicit stress-induced behavioral and endocrine alterations before the onset of drug treatment, and psychosocial stress continued throughout the treatment period of 30 days Clomipramine was administered orally once daily at a dose of 50 mg/kg The drug had a time-dependent restorative influence on marking and grooming behavior, locomotor activity, risk assessment, as well as on urinary cortisol and norepinephrine excretion It, thus, appears that the clomipramine treatment counteracts the behavioral and endocrine effects of chronic psychosocial stress in tree shrews, and the time course of recovery corresponds closely to that observed when treating depressed patients in the clinic

Neurochemical and neurobehavioral effects of repeated gestational exposure to chlorpyrifos in maternal and developing rats

Abstract: Acute exposure to the organophosphate pesticide chlorpyrifos (CPF) on gestation day 12 (GD12, 200 mg/kg/ml, SC) causes extensive neurochemical changes in maternal brain but lesser changes in fetal brain. In the present study, we examined the relative neurotoxicity of repeated, lower-level CPF exposures during gestation in rats. Pregnant Sprague-Dawley rats were exposed to CPF (6.25, 12.5, or 25 mg/kg per day, SC) from GD12-19 and sampled at either GD16, GD20, or postnatal day 3 (PND3) for measurement of various maternal and developmental neurochemical markers. In contrast to the high acute dose exposure, no maternal toxicity was noted with repeated lower-level dosing. Extensive acetylcholinesterase (AChE) inhibition (83-90%) was noted in maternal brain at all three time points following repeated exposures (25 mg/kg). Higher AChE inhibition (58%) was noted in fetal brain at GD20 compared to 19-25% on PND3 in treated pups cross-fostered to control dams and in control pups cross-fostered to treated dams following repeated exposures (25 mg/kg per day). Whereas similar reductions in brain muscarinic receptor binding were noted at GD20 and PND3 in dams and developing brain between acute and repeated dosing regimens, greater changes in [3H]CD and [3H]cytisine binding were evident following repeated exposures. Righting reflex and cliff avoidance tests were markedly altered following repeated exposures. The results suggest that lower-level repeated exposures to CPF cause extensive neurochemical and neurobehavioral changes in developing rats in the absence of maternal toxicity.

Role of 5-HT1A receptors in the effects of acute and chronic fluoxetine on extracellular serotonin in the frontal cortex

Abstract: Fluoxetine 10 mg/kg i.p. significantly increased the extracellular concentrations of serotonin (5-HT) in the frontal cortex as assessed by in vivo microdialysis. This effect was significantly potentiated when 0.3 mg/kg s.c. WAY-100635, a 5-HT1A receptor antagonist, was administered 30 min before. WAY-100635 by itself had no effect on extracellular 5-HT. Twenty-four hours after chronic fluoxetine schedule (10 mg/kg/day i.p. x 14 days), basal extracellular 5-HT concentrations in the frontal cortex were higher than those of animals that had received the vehicle chronically. At 24 h after the last dose, a challenge dose of fluoxetine (10 mg/kg i.p.) raised extracellular 5-HT similarly in chronically vehicle or fluoxetine treated rats. At this same interval 25 micrograms/kg s.c. 8-OH-DPAT, a 5-HT1A receptor agonist, significantly reduced extracellular 5-HT only in the frontal cortex of rats treated chronically with the vehicle. Examining basal extracellular 5-HT, the effect of a challenge dose of fluoxetine and the effect of 25 micrograms/kg 8-OH-DPAT after 96 h washout, no differences were found between chronically fluoxetine and vehicle-treated rats. The results confirm that the ability of fluoxetine to stimulate 5-HT1A autoreceptors through an increase of endogenous 5-HT attenuates its effect on cortical dialysate 5-HT. Chronic fluoxetine increased the basal concentrations of extracellular 5-HT only when a substantial amount of its metabolite was present in the brain and during the desensitization of presynaptic 5-HT1A autoreceptors (24 h after the last dose). These effects, in fact, disappeared after 96 h washout. The continuous presence of the drug may, therefore, be necessary to maintain extracellular 5-HT at concentrations high enough to produce a therapeutic effect.

Dissociating the nicotine and airway sensory effects of smoking

Abstract: This study examined the subjective and cardiovascular effects of two of the components of cigarette smoking when given separately: nicotine and airway sensations. Using a within-subjects design, six healthy volunteer smokers, age 18–45 years, who smoked at least 20 cigarettes per day were given six conditions in a randomized, counterbalanced order. The effects of IV nicotine, IV saline, and denicotinized cigarettes were compared to a standard 1-mg cigarette. The standard cigarette produced more of a calming effect and more irritability reduction than either the nicotine or airway sensations alone. The denicotinized cigarette was similar to the standard cigarette condition, except the cigarette condition was associated with higher feelings of “exhilaration.” Many of the positive subjective effects from a denicotinized cigarette were comparable to that of a standard cigarette. These data support the hypothesis that replacement of the sensory cues of smoking with “airway sensory replacement” may be useful for smoking cessation.

Teratogenic actions of ethanol in the mouse: a minireview.

Abstract: The deleterious effects of prenatal ethanol exposure have been extensively documented in clinical and experimental studies. This paper provides an overview of work conducted with mice to examine the myriad of adverse consequences that result from embryonic/fetal exposure to ethanol. All of the hallmark features of the clinical fetal alcohol syndrome have been demonstrated in mice, including prenatal and postnatal growth retardation, structural malformations and behavioral abnormalities associated with central nervous system dysfunction. As expected, the severity and profile of effects is related to both dosage level and timing of exposure. In addition, these effects have been demonstrated following acute and chronic exposure, with a variety of routes of administration employed. Furthermore, a number of strains have been used in these studies and the variant response (susceptibility) to the teratogenic actions of ethanol exhibited among different mouse strains support the notion that genetic factors govern, at least in part, vulnerability to these effects of ethanol. More recent studies using mouse models have focused on examining potential mechanisms underlying the full spectrum of ethanol's teratogenic actions.

Behavioral stress response of genetically selected aggressive and nonaggressive wild house mice in the shock-probe/defensive burying test.

Abstract: Genetically selected aggressive and nonaggressive male wild house mice were tested in the shock-probe/defensive burying test. Five distinct behaviors (burying, immobility, rearing, grooming, and exploration) were recorded in two environmental situations: fresh and home cage sawdust. Nonaggressive animals, characterized by a Long Attack Latency (LAL), showed more immobility in both test situations than animals having Short Attack Latencies (SAL), whereas SAL males displayed more defensive burying than LAL ones when tested with fresh sawdust. Testing with home cage sawdust, however, resulted in the same duration of defensive burying in SAL and LAL. These results support earlier findings about the existence of two heritable, fundamentally different strategies to cope with aversive situations. Aggressive (SAL) animals react actively to environmental challenges, whereas nonaggressive animals react actively or passively, depending on the characteristics of the stressful environment. These mouse lines, selected for attack latency, i.e., aggression, may, therefore, be important tools to unravel the genetic architecture underlying the physiological and neuronal mechanisms of behavioral strategies towards stressful events.

Anxiolytic effects in the plus-maze of 5-HT1A-receptor ligands in dorsal raphé and ventral hippocampus.

Abstract: The response of rats naive to, or experienced with, the elevated plus-maze test of anxiety was observed following direct administration of the 5-HT1A-receptor agonist (+/-)-8-hydroxy-dipropylaminotetralin (8-OH-DPAT) (50, 100, or 200 ng) or antagonist tertatolol (3 micrograms) into the dorsal raphe nucleus or bilaterally into the ventral hippocampus. In rats naive to the plus-maze, neither drug had a significant effect when microinjected into the dorsal raphe nucleus. However, in rats experienced with the plus-maze, 8-OH-DPAT (100 and 200 ng) had significant anxiolytic effects when administered to the dorsal raphe nucleus, which were antagonised by tertatolol (3 micrograms); this suggests they were mediated by 5-HT1A receptors. Hyperactivity (increased number of closed-arm entries) was found following bilateral injection of 8-OH-DPAT (100 ng) into the ventral hippocampus of rats naive to the plus-maze. This was not completely antagonised by tertatolol (3 micrograms). Interestingly, tertatolol (3 micrograms) itself had an anxiolytic effect which was not antagonised by 8-OH-DPAT (100 ng), suggesting the effect was not mediated by 5-HT1A receptors, and indeed other actions of tertatolol, such as those on 5-HT1B or beta-adrenergic receptors could have been involved. In rats experienced with the plus-maze, tertatolol (3 micrograms) again had a significant anxiolytic effect when administered bilaterally to the ventral hippocampus, and again, this was not antagonised by 8-OH-DPAT (100 ng). These results demonstrate that both the intracerebral location of the injection and test experience profoundly influence the effects of 5-HT1A ligands on behaviour of rats in the elevated plus-maze test of anxiety.

Plus-maze retest profile in mice: Importance of initial stages of trial 1 and response to post-trial cholinergic receptor blockade

Abstract: Recent research has shown that a single undrugged prior experience of the elevated plus-maze produces significant behavioural changes upon 24-h retest in rats and mice. Typically, when reexposed to the maze, animals display an increased avoidance of the open arms and a corresponding preference for the enclosed sections of the apparatus. Using ethological analyses, the present series of experiments sought to further characterize this phenomenon in mice and to determine whether or not it involves cholinergic receptor mechanisms. Results confirmed that behaviour during Trial 2 is markedly different to that seen on initial exposure, and that such changes are independent of the duration of Trial 1 (2 vs. 5 min). Retest behavioural changes included reduced entry latencies, reduced open arm entries, less time on the open arms and centre platform, lower levels of exploratory head-dipping, and increased entries into and time spent in the closed arms. The importance to the retest phenomenon of the first few minutes of initial exposure was further suggested by min-by-min analyses of the behaviour of animals naive to the maze. Results showed that behaviour during the first min is characterized by high levels of risk assessment from the centre platform and relatively low, but equal, levels of open- and closed-arm exploration. From min 2 onwards, however, behaviour showed a marked change with increasing open arm/centre platform avoidance, increasing closed-arm preference, and decreasing levels of risk assessment and exploratory head-dipping. Thus, it would appear that this within-session aversive learning transfers between sessions to account for behavioural profiles on retest. Irrespective of the duration of Trial 1 (2 or 5 min), posttrial administration of the muscarinic antagonist, scopolamine (0.1-1.0 mg/kg), failed to significantly alter the behavioural changes seen between trials. Data are discussed in relation to the apparent sensitization of fear produced by plus-maze exposure, its possible relation to phobia acquisition, and the need for further research on underlying mechanisms.

Stress and the immune system in the etiology of anxiety and depression.

Abstract: There is clinical and experimental evidence that various aspects of the immune and endocrine systems are severely compromised in chronic stress and depression. For example, it has been shown that a reduced lymphocyte response occurs to mitogens in depressed patients, effects that are not reversed by chronic antidepressant treatment. By contrast, monocyte phagocytosis is increased, while neutrophil phagocytosis is decreased in depressed patients. Such changes are normalized by effective antidepressant treatment. The results of such studies and others that demonstrate alterations in noncellular immune processed in depression indicate that the changes in immune function correlate with the severity and duration of the external and/or internal stressful stimuli. There is evidence that some of the immune changes are a reflection of increased plasma glucocorticoids that characterize both stress and depression. However, it is also apparent that the cytokines, prostaglandins, and corticotrophic releasing factor (CRF) also play an important role in initiating the behavioral and pathophysiological changes that are characteristic of both depression and chronic stress. This review attempts to critically assess the interplay between CRF, the immune and neurotransmitter systems, and behavior in chronic stress and depression.

Effect of Chronic Mild Stress on Circadian Rhythms in the Locomotor Activity in Rats

Abstract: The purpose of this study was to assess whether the chronic mild stress (CMS) procedure, as a realistic animal model of depression, affects the rhythms of the locomotor activity in rats. Rhythm parameters (period, mesor, amplitude, acrophase, and percent rhythm) were estimated from the best-fitted cosine function curves. Period is the length, mesor is the mean level, amplitude (A) is the extent, acrophase is the timing of the rhythm; percent rhythm represents the variability estimated by the cosine regression and expressed as a percentage of the total variability of raw data. The animals were kept on the 12 L : 12 D cycle during 13 weeks of the experiment and subjected to CMS for first 4 weeks. In week 5 the rats were under the constant light for 24 h a day (LL), and in week 9, under the constant darkness (DD). In LD 12:12 CMS decreased the activity in the dark phase by approximately 50% (p < 0.01) and did not change the activity in the light phase, resulting in a drop of the 24 h activity by about 40% in comparison to controls. The amplitude of diurnal variations of the activity was highly statistically different from zero at p(A = 0) < 0.0001, and the percent rhythm was in range of 40-75% in both the CMS and control groups. The mesor and the amplitude of the diurnal rhythm (with a period of 24 h) in the CMS rats were significantly (p < 0.001) lower than those in the control. In LL, the activity of both groups was diminished about 50% during the subjective dark phase. On the other hand, in the subjective light phase the activity of CMS rats only was diminished. The percent rhythm for the CMS and control rats was 30 and 58%, respectively, and values of mesor, amplitude, and acrophase for both groups were highly statistically different. In DD, the activity in the CMS group was statistically significantly lower in both the subjective dark and light phases. In contrast to the results from LL, the cosine curves from DD were similarly shifted in relation to the subjective light-dark cycle. After a restoration of the LD cycle the levels of the 24-h activity of both groups became equal in the 13th week, but the light and dark phase differences between the groups were still statistically significant (p < 0.05). The present results indicate that CMS exerts distinct and prolonged disturbances of the diurnal and circadian rhythms of the locomotor activity in the rats.

Strain Differences in Fear-Motivated Behavior of Rats

Abstract: Studies have shown different and sometimes contradictory results in response to anxiolytic drugs. In the present study, the behavioral performance of rat strains, obtained from different breeders, was examined in four animal models of anxiety- or in exploration-related behavior to assess the potential contribution of genetic disposition or breeding factors to aversion-motivated behavior. Male rats: Wistar/Winkelmann, Wistar/Charles River, Wistar/BGVV, Lewis/Charles River, Fischer/Charles River, Brown Norway/Charles River were used in a conflict test in the open field, a free exploratory paradigm, social interaction test, and the holeboard test. The results show that robust behavioral differences in anxiety or exploration exist between different strains of rats and animals of one strain, obtained from different breeders. The differences shown in anxiety-related behavior might explain sometimes contradictory effects following the treatment with anxiolytic or anxiogenic drugs. The results indicate that genetic factors and breeding conditions substantially contribute to anxiety-motivated behaviors in animal models of anxiety. These differences in anxiety-related behavior may also be related to biochemical differences.

The NMDA antagonist memantine blocks the expression and maintenance of morphine dependence

Abstract: The ability of memantine (1-amino-3,5-dimethyladamantane) to block the expression and maintenance of morphine dependence was examined in mice. When administered to morphine-dependent mice 45 min prior to naloxone challenge, memantine (7.5–30 mg/kg IP) in a dose-dependent manner reduced jumping behavior (a manifestation of the expression of dependence). The ability of memantine to attenuate naloxoneprecipitated jumping was reversed by administration of glycine, an observation consistent with electrophysiological studies indicating that memantine is a use-dependent (uncompetitive) N- methyl - d - aspartate (NMDA) antagonist. In an independent series of experiments, the effect of memantine on a preestablished morphine dependence was investigated. A residual dependence to morphine was present 3 days after cessation of morphine administration. Repeated administration of memantine (10 mg/kg, IP) or the competitive NMDA antagonist NPC 17742 [2R,4R,5S-(2-amino-4,5-(1,2-cyclohexyl)-7-phosphonoheptanoic acid)] (6 mg/kg, IP) during this 3-day period abolished subsequent naloxone-precipitated jumping. In contrast, when administered concurrently with morphine after dependence had already been well established, memantine (10 and 20 mg/kg, IP) did not affect the maintenance of morphine dependence. Based on these findings, NMDA antagonists appear to inhibit the maintenance of opioid dependence, an action distinct from their acute inhibitory effects on the expression of dependence. Nonetheless, these regimen-dependent effects of memantine indicate that the most efficacious use of NMDA antagonists would be in detoxified subjects, rather than in individuals with an established dependence who are currently abusing opioids.

Dorsomedial hypothalamic GABA dysfunction produces physiological arousal following sodium lactate infusions

Abstract: Since impairing gamma-aminobutyric acidA (GABAA) receptor-mediated inhibition in the dorsomedial hypothalamus (DMH) of rats elicits a panic-like response, experiments were conducted to test if rats with GABA dysfunction in the DMH would be vulnerable to precipitation of a panic-like response after intravenous sodium lactate infusions. Rats were implanted with unilateral infusion cannula into the DMH which were connected with Alzet minipumps that chronically infused (3.5 nmol/microliter /h) either a-CSF (vehicle), dl-(racemic), l-(active) or d-(inactive) isomers of allylglycine (AG), an inhibitor of GABA synthesis. Another group of rats had l-allylglycine pumps implanted in the paraventricular nucleus of the hypothalamus (PVN) as anatomical controls. Animals were tested in the social interaction (SI) test and given sodium lactate infusions (10 ml/kg/15 min) before Alzet pump implantations and on days 4, 7, and 14 after pump placement. Rats were also tested in the elevated plus-maze on treatment day 4. Chronic impairment of GABA function in the DMH and not PVN resulted in rats being more anxious in the SI test on treatment days 4, 7, and 14 and in the elevated plus-maze on day 4 compared to a-CSF and d-AG infusions. Further, rats with GABA dysfunction in the DMH, and not PVN, exhibited significant increases in heart rate and blood pressure following IV sodium lactate infusions. There were significant decreases in DMH glutamic acid decarboxylase activity and GABA content in rats receiving 7 days of dl-AG or l-AG infusions. These results indicate that chronic reduction of GABA function in the DMH leads to the development of panic-like disorder in this animal model.

Recent developments in anxiety, stress, and depression

Abstract: Recent research in the development, analysis, and pharmacology of animal tests of state anxiety is discussed, including the use of responses to predator odours, the role of learning in modifying the anxiety measured in the plus-maze, and the roles of cholinergic, NMDA, and dopaminergic systems. Developmental and genetic factors are considered with particular reference to the development of tests of trait anxiety. The roles of 5-HT1A receptors in anxiety, depression, impulsivitity, and agonistic behaviours are discussed. Recent studies on the impacts of stress on neurotransmitter, endocrine, and immune systems and the interactions between these systems are discussed, with particular emphasis on their contributions to the development of pathologic states relevant to anxiety and depression.

Serotonergic activation reduces defensive freezing in the conditioned fear paradigm

Abstract: Our previous study showed that conditioned fear stress (CFS) increased serotonin (5-HT) metabolism in the medial prefrontal cortex and induced freezing behavior. Although these results could support the 5-HT hypothesis of anxiety, the functional significance of the 5-HT response to stress is unclear. In this study, the effects of 5-HT reuptake inhibitors, agonists, antagonists, and diazepam on freezing behavior induced by CFS were examined using a time-sampling procedure. Various doses of test compounds were administered subcutaneously to rats 24 h after the last session of repeated foot-shock for 5 days. Rats were again placed in the shock chamber without shocks 20 min after injections of drugs, and observed. Diazepam (1 mg/kg) and the 5-HT1A agonist ipsapirone (0.5–10 mg/kg) significantly inhibited freezing behavior. l-5-Hydroxytryptophan (with benserazide) and the selective 5-HT reuptake inhibitor citalopram (10 mg/kg) reduced freezing behavior. The 5-HT2 antagonists ICI169,369 and ketanserin failed to change freezing behavior. p-Chlorophenylalanine (200 mg/kg) administered 15 h before the test did not affect freezing. The effect of ipsapirone was not modified in rats with lesions of 5-HT neurons, produced by p-chloroamphetamine (2 × 10 mg/kg). In conclusion, these results suggest the anxiolytic potential of ipsapirone and citalopram, and support the hypothesis that the facilitation of 5-HT neurotransmission decreases anxiety.

Effects of nicotine withdrawal on central dopaminergic systems

Abstract: The behavioral and neurochemical manifestations in rats 24 h following the cessation of 14-day nicotine administration were investigated. Animals were implanted subcutaneously with osmotic minipumps which continuously released either saline or nicotine (1.5 mg/kg/day or 3.0 mg/kg/ day) for 14 days. After the animals were withdrawn from nicotine for 24 h, we observed a significant decrease of locomotor activities and a reduction of dopamine contents in the striatum and nucleus accumbens. Nicotine withdrawal did not affect the body weight, food, or water consumption, and no deficit in the acquisition of a conditioned avoidance task was found in these animals. In addition, nicotine withdrawal did not alter the density or the binding affinity ( K d ) of ligands to D 1 and D 2 receptors in the striatum. Although nicotine withdrawal did not alter the density or binding affinity of ligands to D 1 receptors in the nucleus accumbens, the maximum number of D 2 receptor sites were reduced by nicotine treatment. These results offer possible neurochemical mechanisms for changes of locomotor activity which occurred in rats during nicotine abstinence.

Stress-induced increase in brain neuroactive steroids: Antagonism by abecarnil

Abstract: Acute foot shock stress elicits a selective and time-dependent increase of neuroactive steroid (pregnenolone, progesterone, allotetrahydrodeoxycorticosterone) concentrations in rat brain cortex, accompanied by a marked increase of plasma corticosterone. The brain cortical neuroactive steroid levels peaked between 10 and 30 min poststress and returned to control values by 2 h. Abecarnil (0.3 mg/kg), i.p.), a beta-carboline derivative with anxiolytic properties, completely antagonized the effect of foot shock on brain cortical neuroactive steroids. A single administration of the anxiogenic beta-carboline FG 7142 (15 mg/kg, i.p.), in contrast, mimicked the effect of foot shock. These data support the hypothesis for the existence of a functional relationship between brain neuroactive steroid concentrations and GABAA receptor function/emotional state of the animal.

Entrainment of circadian rhythms by S-20098, a melatonin agonist, is dose and plasma concentration dependent

Abstract: The present study determined first the dose-response (0.5 to 10 mg · kg −1 ) to daily oral administration of S-20098, a melatonin agonist, in entraining circadian rhythms of rats free-running in constant darkness; second, the relation between entrainment and the plasma concentration of S-20098. Finally, responses to 8 mg · kg −1 of S-20098 were compared with those obtained with the same dose of melatonin and ipsapirone. Responses were classified as negative, transient, or true entrainment. The data indicated a clear dose-dependent response from 2.5 to 10 mg · kg −1 of S-20098 with an ED 50 of 5.7 mg · kg −1 for true entrainment and a clear relation between entrainment and the plasma concentration of S-20098. S-20098 was as effective as melatonin to entrain free-running rhythms. Ipsapirone was ineffective in our experimental conditions.

Neurosteroids block the memory-impairing effects of ethanol in mice

Abstract: Using a win-shift foraging paradigm to assess working memory in C57BL/6 mice, the memory-enhancing effect of low doses of the neurosteroids 5-pregnen-3β-ol-20-one [pregnenolone (PE)], 5-pregnen-3β-ol-20-one sulfate [pregnenolone sulfate (PS)], 5-androsten-3β-ol-17-one [dehydroepiandrosterone (DHEA)], and 5-androsten-3β-ol-17-one sulfate [dehydroepiandrosterone sulfate (DHEAS)] were demonstrated. The neurosteroids 5β-pregnan-3α-ol-20-one [pregnanolone (PA)] and 5β-pregnan-3β-ol-20-one [epipregnanolone (EPI)] disrupted memory in this paradigm. PE, PS, DHEA, DHEAS, and PA were also capable of blocking the memory-impairing effect of 0.5 g/kg ethanol. EPI prevented PA from blocking the effect of ethanol. The influence of these compounds on memory and their interactions on this behavior are consistent with their actions on the GABA A system.

Genetic differences in tolerance and sensitization to the sedative/hypnotic effects of alcohol.

Abstract: Initial sensitivity to alcohol and the development of alcohol tolerance were examined in rats of the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines. All rats received two alcohol injections (3.0 g/kg b.wt., IP) separated by either 1 or 2 days. P rats were less sensitive to the behaviorally impairing effects of alcohol than were NP rats, as evidenced by a longer latency to lose righting reflex (RR) and a shorter time to recover RR following an initial alcohol injection. When 1 day separated the two alcohol injections, P rats recovered the RR more rapidly following a second injection compared to the first, indicating that the P rats developed tolerance to the sedative/hypnotic effects of alcohol. In contrast, the NP rats recovered the RR more slowly following the second injection compared to the first, indicating that the NP rats developed sensitization to alcohol. Tolerance in the P line and sensitization in the NP line disappeared when 2 days separated the two alcohol injections. Line differences in initial sensitivity and tolerance/sensitization to the behaviorally impairing effects of alcohol may contribute to the differences in alcohol consumption observed in the P and NP lines.

Reduced evoked release of acetylcholine in the rodent hippocampus following traumatic brain injury

Abstract: The chronic effects of traumatic brain injury on acetylcholine release were evaluated by using in vivo microdialysis. Acetylcholine release was measured in the hippocampus of anesthetized rats 2 weeks after lateral controlled cortical impact (n = 10) or sham surgery (n = 10). Prior to microdialysis, behavioral assessments of motor and spatial memory were performed. Cortical impact (6 meter/s, 2 mm deformation) produced beam balance deficits that persisted for 1 day and beam walking deficits that persisted for 3 days after injury. In addition, spatial memory, as measured by swim latencies in a Morris water maze, was compromised between 10-14 days after injury. Immediately following behavioral testing, the animals were anesthetized with halothane, and a microdialysis probe was placed into the dorsal hippocampus. After a 160 min equilibration period, extracellular levels of acetylcholine were measured prior to and after an intraperitoneal administration of scopolamine (1 mg/kg), which evokes acetylcholine release by blocking autoreceptors. Prior to scopolamine administration, there were no differences in extracellular levels of acetylcholine between injured and sham animals. However, there was a significant reduction of hippocampal acetylcholine release evoked by scopolamine in injured animals as compared to sham controls. In separate control groups, saline administration alone did not change hippocampal acetylcholine release in injured (n = 5) or sham (n = 5) animals. This study represents the first application of in vivo microdialysis to evaluate chronic neurotransmission deficits following TBI. The present study demonstrates that a magnitude of traumatic brain injury (TBI) sufficient to produce spatial memory deficits can result in a reduction in scopolamine-evoked release of acetylcholine within the hippocampus. The data further suggest that presynaptic mechanisms mediating release of acetylcholine could play a significant role in cholinergic neurotransmission deficits following TBI.

Paternal exposures: impact on reproductive and developmental outcome. An overview.

Abstract: Experimental and epidemiologic investigations document the adverse consequences of an array of paternal exposures on the development of subsequent offspring. Male-mediated abnormalities have been reported after exposure to therapeutic and recreational drugs, to chemicals in the workplace and environment and to ionizing radiation. The impact on progeny outcome includes: an increase in congenital malformations, spontaneous abortions, fetal resorptions; low birth weight; increase in childhood cancers; developmental, neurobehavioral, neuroendocrine, neurochemical abnormalities; effects in F2 generation progeny. Fertility is often unaffected. The comparative influence of genetic, epigenetic and nongenetic mechanisms in the etiology of paternally-mediated adverse outcomes is unknown. There is no a priori reason to assume that male-mediated effects are limited to the agents studied to date. The broad spectrum of alterations recorded after exposure to a variety of unrelated agents suggests the need for a more focused effort and multidisciplinary exploration of the potential impact of the male parent on reproductive outcome.

Affiliation in periadolescent rats: Behavioral and corticosterone response to social reunion with familiar or unfamiliar partners

Abstract: The aim of this study was to investigate whether the social relationship between periadolescent rats, which is characterized by a high expression of play behavior, resembles attachment or whether it reflects a nonspecific social attraction between peers Sprague-Dawley rats have been kept in pairs with a conspecific of the same age and sex from the time of weaning (PND 21) On PND 34, the members of each pair were separated for a 24-h period and randomly assigned to one of three groups: a) immediately sacrificed (NT = nontreated); b) reunited for 30 min with their previous cagemate (FAM); or c) with an unfamiliar conspecific of the same age and sex (UNF) During the reunion, the occurrence of both social and nonsocial behaviors was scored Overall, periadolescent UNF animals spent more time in social investigation than FAM rats, which were conversely more involved in cage-oriented activities In addition, higher levels of rough-and-tumble play were expressed in encounters between UNF subjects than between FAM rats Finally, within the female group, UNF rats were more involved in play soliciting and less in digging activity than FAM animals Blood corticosterone levels, which were measured at the end of the separation period, were higher in females than in males and were significantly lower than following reunion in a novel environment The degree of familiarity did not affect hormonal changes Results suggest that periadolescent rats do not form attachment relationships with each other However, partner familiarity appears to be an important variable affecting social relationships

Inhibitors of protein and RNA synthesis block context memory and long-term habituation in the crab Chasmagnathus

Abstract: The crab Chasmagnathus granulatus reacts to a shadow passing overhead (a danger stimulus) with an escape response that habituates quickly and for at least 5 days. Recently, it has been reported that cycloheximide (CY) disrupts this long-term habituation and the corresponding context memory. In the present article, experiments with CY and an inhibitor of RNA synthesis, actinomycin-D (ACT), were parallelly conducted. An injection of CY (20 μg) or ACT (0.62 μg) reduced the incorporation of [14C]-aminoacid into cerebral plus thoracic ganglia by 80% for 2 h and 59.7% for 1 h, respectively, but no inhibition was found at 24 h. Both ACT (0.62 μg) and CY (20 μg) administered immediately after training (15 trials with the danger stimulus) impaired either long-term habituation or context memory when tested at 24 h. Because ACT and CY have in common only their direct or indirect inhibitory effect on protein synthesis, this finding is considered as an additional evidence that long-term memory in Chasmagnathus requires de novo protein synthesis. However, pretraining ACT or CY impaired context memory at 24 h but not long-term habituation. Such a disparity is explained by an unspecific attenuating effect upon the response, attributed to drug × training interaction. Neither ACT nor CY affected short-term habituation.