Influence of reactivity to novelty and anxiety on hypothalamic–pituitary–adrenal and prolactin responses to two different novel environments in adult male rats

Since stressor-induced activation of the hypothalamic-pituitary-adrenal (HPA) axis is involved in some stress-related pathologies, much attention has been paid in laboratory animals to the study of the relationship between endocrine, particularly HPA, responsiveness to stressors and other individual characteristics, such as reactivity to novelty and fear/anxiety. In the present study, adult male rats were classified as high or low reactive to novelty (HR versus LR), as a function of the horizontal activity displayed during 30 min in a circular corridor, and as high or low anxiety (HA versus LA) as a function of the time spent in the open arms of the elevated plus-maze. Then, the behavioural and hormonal response to two distinct novel environments (the hole-board and the light-dark) was assessed in the same subjects, using a counterbalanced design. Plasma prolactin, ACTH and corticosterone responses to the hole-board were higher than to the light-dark, a good correlation between the two tests being found for each hormone. Whereas the hormonal response to the novel environments was not affected by anxiety, HR rats showed a consistently higher HPA response than LR rats when the criteria to classify the animals were the activity during the first 15 min in the circular corridor, but not when the activity during the second 15 min was considered. Neither trait affected prolactin response. The present results demonstrate a good within-individual consistency of the endocrine response to novel environments and support the hypothesis of a higher HPA response to stressors for HR versus LR rats. In contrast, no contribution of fear/anxiety to endocrine responsiveness was observed.

Perseverance of exploration in novel environments predicts morphine place conditioning in rats

Reactivity to novelty has been related to operant drug self-administration but does not seem involved in the conditioned place preference (CPP). To further assess this issue our aims were to investigate: (1) the importance of the initial versus delayed activity in the novel environment to predict the CPP induced by morphine; (2) the separate contribution of trait anxiety in morphine CPP. Male Sprague-Dawley rats were exposed to a circular corridor for 30 min to assess reactivity to novelty and to the elevated plus-maze and the light-dark tests as measures of anxiety and morphine CPP was then studied (three pairings with 5 mg/kg s.c. morphine and three with saline). Delayed activity in the corridor (16-30 min) correlated positively with CPP score, whereas the initial activity (0-15 min) did not. High-responders (HR), those more active during the second half of the corridor, developed morphine CPP in contrast to low-responders (LR). Also, HR and LR did not differ in anxiety nor any plus-maze or light-dark test measure correlated with CPP behaviour. Enhanced vulnerability to develop morphine CPP is predicted by a higher delayed activity in a novel environment, regardless of anxiety.

Responsiveness of the hypothalamic-pituitary-adrenal axis to different novel environments is a consistent individual trait in adult male outbred rats

Susceptibility to some stress-induced pathologies may be strongly related to individual differences in the responsiveness of the hypothalamic-pituitary-adrenal (HPA) axis to stressors. However, there have been few attempts in rodents to study the reliability of the individual differences in the responsiveness of the HPA to stressors and the relationship to resting corticosterone levels. In the present work, we used a normal population of Sprague-Dawley rats, with a within-subject design. Our objectives were to study: (a) the reliability of the ACTH and corticosterone response to three different novel environments widely used in psychopharmacology and (b) the relationship between stress levels of HPA hormones and the daily pattern of corticosterone secretion (six samples over a 24-h-period). Animals were repeatedly sampled using tail-nick procedure. The novel environments were the elevated plus-maze, the hole-board and the circular corridor. Animals were sampled just after 15 min exposure to the tests and again at 15 and 30 min after the termination of exposure to them (post-tests). The hormonal levels just after the tests indicate that the hole-board seems to be more stressful than the circular corridor and the elevated plus-maze, the latter being characterized by the lowest defecation rate. Correlational analysis revealed that daily pattern of resting plasma corticosterone levels did not correlate to HPA responsiveness to the tests, suggesting no relationship between resting and stress levels of HPA hormones. In contrast, the present study demonstrates, for the first time, a good within-subject reliability of the ACTH and corticosterone responses to the three environments, suggesting that HPA responsiveness to these kind of stressors is a consistent individual trait in adult rats, despite differences in the physical characteristics of the novel environments.

The hypothalamic–pituitary–adrenal and glucose responses to daily repeated immobilisation stress in rats: individual differences

It is accepted that there are important individual differences in the vulnerability to stress-induced pathologies, most of them associated to the hypothalamic-pituitary and sympatho-medullo-adrenal axes, the two prototypical stress-responsive systems. However, there are few studies specifically aimed at characterising individual differences in the physiological response to daily repeated stress in rats. In the present work, male rats were submitted to repeated immobilisation (IMO) stress (1 h daily for 13 days) and several samples were taken at specific days and time points. Animals only subjected to blood sampling procedure served as controls. Daily adrenocorticotropic-hormone (ACTH), corticosterone and glucose responses to immobilisation (that included the post-immobilisation period) progressively declined over the days. In addition, repeated immobilisation resulted in decreased relative thymus weight, increased relative adrenal weight, elevated corticotropin-releasing factor (CRF) mRNA levels in the hypothalamic paraventricular nucleus (PVN), and down-regulation of glucocorticoid receptor gene transcription in hippocampus CA1. However, only CRF mRNA levels in the paraventricular nucleus correlated with the ACTH (on day 1) and corticosterone responses (from day 4-13) to immobilisation. When the animals were classified in three groups on the basis of their plasma ACTH levels immediately after the first immobilisation, individual differences in the ACTH response progressively disappeared on successive exposures to the stressor, whereas those in corticosterone and glucose were more sustained. The present results suggest that there are individual differences in the physiological response to stress that tend to be reduced rather than accentuated by repeated exposure to the stressor. Nevertheless, this buffering effect of repeated stress was dependent on the particular variable studied.

Wood-smoke exposure: an unusual cause of miliary mottling on X-ray chest

A case of wood smoke inhalation related lung disease presenting with miliary mottling on radiography is described. Transbronchial lung biopsy showed the presence of coal macules.

Parafascicular electrical stimulation attenuates nucleus basalis magnocellularis lesion-induced active avoidance retention deficit

Previous experiments from our laboratory showed that retention of two-way active avoidance learning is improved by post-training intracranial electrical stimulation (ICS) of the parafascicular nucleus (PF) and impaired by pre-training electrolytic lesions of the nucleus basalis magnocellularis (NBM). The question investigated here was whether post-training PF ICS is able to attenuate the active avoidance retention deficit observed in rats lesioned pre-training in the NBM. To this goal, the following experimental design was used: rats bilaterally lesioned in the NBM and stimulated in the PF, rats lesioned in the NBM, rats stimulated in the PF, control rats implanted in the PF, and sham-operated rats were first trained in a shuttle-box for a single 30-trial session and tested again following two successive retention intervals (24 h and 11 days). The results showed that: (1) NBM lesions impaired the 11-day performance without affecting either the acquisition or the 24-h retention of the avoidance learning; (2) PF ICS treatment in unlesioned rats improved performance in both retention sessions only when the stimulation was applied in the posterior region of the nucleus; and (3) stimulation of the posterior PF compensated the 11-day retention impairment induced by NBM lesions. These results are discussed in relation to the interaction of arousal systems in the modulation of cognitive processes.

Opposite effects of ethanol and ketamine in the elevated plus-maze test in Wistar rats undergoing a chronic oral voluntary consumption procedure

The anxiolytic effects of ethanol (EtOH) have been involved in the vulnerability to EtOH drinking in humans. However, the role of the anxiolytic effects of EtOH during a chronic ingestion of the drug has not been extensively addressed, either in humans or in animal models. Since it was first shown that EtOH interacts with the N-methyl-d-aspartate (NMDA) receptor, a growing body of evidence demonstrating the involvement of this receptor in a wide range of EtOH effects has been reported. The present study aimed to investigate the ability of a voluntary consumption of EtOH to exert its putative anxiolytic-like activity in non-selected male Wistar rats held under a voluntary chronic oral consumption procedure using the elevated plus-maze (EPM) test. The effects of EtOH were compared with those of the noncompetitive NMDA receptor antagonist ketamine (KET), and with a mixture of both drugs. Rats were provided with 1-h limited access to one of the following sweetened (10% w/v glucose) solutions: (i) control; (ii) EtOH (ethanol, 10% v/v); (iii) KET (ketamine HCl, 0.28 mg/ml); or (iv) mixed (EtOH 10% v/v plus ketamine HCl 0.28 mg/ml) for 35 consecutive days. At the end of this period, and immediately after the last 1-h access to the respective solution, animals were independently tested in either EPM or open field tests. Previously, rats were tested on the inclined screen test during 15 consecutive days. The opposite effects were observed with EtOH and KET consumption in the EPM test, with EtOH decreasing and KET increasing the percentage of time spent in the open arms of the EPM, which was shown to be independent of any locomotor impairment, whereas consumption of the mixed solution did not significantly affect any test. Since the EtOH did not exhibit anxiolytic-like effects after its chronic oral consumption, it might be hypothesized that the anxiolytic activity of the EtOH is not critically involved in the maintenance of a voluntary EtOH consumption in non-selected rats. On the other hand, the lack of effects from mixed solution consumption suggests that EtOH and KET may interact in such a way that their effects are neutralized.

Effects of fimbria lesions on trace two-way active avoidance acquisition and retention in rats

The fimbria-fornix (FF) is the main subcortical input to the hippocampus. It has been shown that FF lesions facilitate performance on a standard-delay two-way active avoidance task (AA2), thought to involve implicit memory. The hippocampal region is required for explicit or relational memory. It has been proposed that the hippocampus and related structures might associate events that are separated in space or time and detect elements shared in common by such discontiguous episodes. Therefore, FF lesions would be expected to impair performance on a trace paradigm, which introduces an interval between the CS (conditioned stimulus) and the US (unconditioned stimulus) and is generally considered a model of explicit memory. We predicted that FF lesions would impair memory in a trace AA2 procedure, while the same lesions would facilitate memory in a standard delay version of the task. To test this hypothesis, two experiments were carried out in 102 male Wistar rats. The first experiment characterized the trace paradigm using this kind of conditioning and demonstrated that control rats were able to acquire and retrieve (24 h and 11 days postacquisition) the association between the CS (tone) and the US (electric foot shock) when a trace interval (5, 10, or 20 s) was interposed between both stimuli. In the second experiment, we investigated the effects of FF electrolytic lesions on the same task using delay and trace (10-s trace interval) paradigms. Surprisingly, FF lesions facilitated the acquisition and the 24-h retention of the AA2 not only on the standard delay paradigm, but also with the trace paradigm. We suggest that facilitative effects could be a result of impairment in contextual learning.

Positive relationship between activity in a novel environment and operant ethanol self-administration in rats

RATIONALE

The study of individual differences in drug addiction may have important implications both for understanding the etiology of addiction and for strategies for treatment. Activity of rodents in novel environments, presumably related to the novelty-seeking trait in humans, is the primary behavioral feature that is hypothesized to predict a predisposition for drug self-administration by rodents.

OBJECTIVES

The aim of this study was to characterize the relationship between motor activity in a novel environment and operant ethanol self-administration using the sucrose-substitution procedure.

METHODS

Male Long-Evans rats were exposed to a novel environment for 2 h, and the distance traversed, rearing, and defecation was recorded. After 3 days of forced exposure to ethanol the sucrose-substitution procedure began and lasted for 23 days. Following sucrose substitution the animals were maintained on a schedule of ethanol (10% v/v) self-administration with a fixed ratio 3 (FR3) for 15 days.

RESULTS

The activity (distance traversed) in the novel environment was positively correlated with initial ethanol self-administration under the FR3 schedule ( r=0.87) but not with the number of inactive lever presses or active lever presses for ethanol or for sweetened ethanol solutions with lower ratios of response. In contrast, rearing was correlated positively only with the number of inactive lever presses for sucrose.

CONCLUSIONS

Motor activity in a novel environment may be related to the acquisition of operant ethanol self-administration only when a given ratio of response is required.

Electrolytic and ibotenic acid lesions of the nucleus basalis magnocellularis interrupt long-term retention, but not acquisition of two-way active avoidance, in rats

Previous experiments on two-way active avoidance have shown conflicting results after nucleus basalis magnocellularis lesion: disrupting effects with electrolytic lesions and facilitative effects with excitotoxic lesions. To resolve this issue, in this experiment, Wistar rats received pre-training bilateral electrolytic or ibotenic acid lesions and were trained in a massed two-way active avoidance conditioning. In order to test the long-term retention of the learned response, one additional session was conducted 10 days after the acquisition. Results showed that whereas electrolytic lesions did not affect the acquisition, ibotenic acid lesions enhanced it. Retention of active avoidance response was impaired by both electrolytic and ibotenic lesions of the NBM. These results suggest a role of the NBM in the memory consolidation and/or retrieval of two-way active avoidance.

Pharmacology of the atypical antipsychotic remoxipride, a dopamine D2 receptor antagonist

Remoxipride is a substituted benzamide that acts as a weak but very selective antagonist of dopamine D2 receptors. It was introduced by Astra (Roxiam) at the end of the eighties and was prescribed as an atypical antipsychotic. This article reviews its putative selective effects on mesolimbic versus nigrostriatal dopaminergic systems. In animals, remoxipride has minimal cataleptic effects at doses that block dopamine agonist-induced hyperactivity. These findings are predictive of antipsychotic activity with a low likelihood of extrapyramidal symptoms. Remoxipride also appears to be effective in more recent animal models of schizophrenia, such as latent inhibition or prepulse inhibition. In clinical studies, remoxipride shows a relatively low incidence of extrapyramidal side effects and its effects on prolactin release are short-lasting and generally mild. The clinical efficacy of remoxipride is similar to that of haloperidol or chlorpromazine. Although its clinical use was severely restricted in 1993, due to reports of aplastic anemia in some patients receiving remoxipride, this drug has been found to exhibit relatively high selectivity for dopamine D2 receptors making remoxipride an interesting tool for neurochemical and behavioral studies.

Short-term natural weathering of MSWI bottom ash

The release of heavy metals from MSWI bottom ash has been the key concern in the management of this material. The leaching distribution values obtained from 100 freshly quenched bottom ash samples, according to the German DIN 38414-S4 procedure test, showed the release of lead, zinc and copper to be the main hazards associated with bottom ash utilisation as a secondary building material. Currently, natural weathering of MSWI bottom ash, for an estimated period of 1-3 months, is the most economic treatment available to ensure the eventual utilisation of this material. The leaching of natural weathered bottom ash in the short-term (up to 9 months) was studied. The most significant changes in the bottom ash were found to occur in the first 90 days. At pH values greater than 12, lead, zinc and copper were the main heavy metals to be released from the MSWI freshly quenched bottom ash samples studied. Natural weathering for a period of about 90 days reduced the leaching of heavy metals, stabilising the bottom ash pH to minimise the solubility of metal hydroxides, and enabled the residue to be used as secondary building material. The profile of the pH neutralisation curve is similar to that described by carbonates, which would suggest that the reaction is controlled by CO(2). The formation of insoluble oxides as well as carbonates control the immobilisation of certain heavy metals, e.g. lead and zinc. The leaching of aluminium increases during this short natural weathering stage due to elemental metal oxidation. Aluminium solubility is controlled by the precipitation of gibbsite or other aluminium-sulphate neoformations. The latter may contribute to the immobilisation of heavy metals.

Acute effects of ketamine in the holeboard, the elevated-plus maze, and the social interaction test in Wistar rats

Although noncompetitive NMDA receptor antagonists have shown an anxiolyticlike profile in several studies, such effects have not been observed consistently. Previous studies with ketamine, a noncompetitive NMDA antagonist, have employed only shock tests of anxiety based on conflict procedures. In the present experiment, the effect of an acute low dose of ketamine (7 mg/kg) was examined in adult male Wistar rats tested in three nonconflict tests: holeboard, social interaction, and elevated plus-maze paradigms. The results showed that ketamine decreased time spent in active social interaction and the number of rearings and central activity in the social interaction test. It also decreased the number of entries into the percentage of time spent in open arms and the total number of entries in the elevated plus-maze. No significant effect was observed in head dipping in the holeboard test, although the number of crossings did increase. These results suggest an anxiogeniclike effect of ketamine in contrast with results previously described for noncompetitive NMDA receptor antagonists. These effects of ketamine are more similar to those described for stimulant drugs such as caffeine, cocaine, or amphetamine in anxiety tests.

Operant ethanol self-administration after nicotine treatment and withdrawal

The effects of chronic intermittent administration of nicotine (NIC) and withdrawal on operant ethanol (EtOH) self-administration were tested in Long-Evans rats (n = 8). EtOH self-administration (10% v/v, Fixed Ratio 4 reinforcement schedule) was induced by the sucrose-substitution procedure. Then the animals were divided into two groups of four rats matched on EtOH self-administration and the locomotor activity following an injection of NIC (0.35 mg/kg, SC) or saline was measured. The groups then received 9 days of injection of either NIC (0.35 mg/kg) or saline and then motor activity was retested using the initial NIC dose. This was followed by 17 days of NIC injections (0.6 mg/kg) or saline injections. A final locomotor test using the higher NIC dose was then conducted. The initial acute administration of NIC had no effect on motor activity compared to saline (measured by the number of horizontal movements). However, after the repeated treatment, the group of animals injected chronically and acutely with NIC showed motor activation in comparison with the animals injected chronically with saline and injected acutely with NIC only on the days of activity testing. At the end of the chronic NIC treatment, operant EtOH self-administration was not changed. However, 6 days after the NIC injections were concluded, a change in the pattern of responding for EtOH was observed in the NIC group, showing a decrease in the mean rate of responding during the first half of the operant self-administration session. When both groups were again tested for locomotor activity at the end of the operant self-administration experiment, the increased motor activity in the NIC group was still observed. The results suggest that alterations in the nicotinic system may affect EtOH self-administration, but this appears to be only modulatory, even with a significant change in locomotor response to NIC following chronic NIC administration.

Effects of nicotine and mecamylamine microinjections into the nucleus accumbens on ethanol and sucrose self-administration

Nicotine (NIC) and ethanol (ETOH) are both drugs of abuse that can affect similar pathways in the central nervous system. However, the role of nicotinic processes in ETOH's reinforcing actions is unclear. Although the mesolimbic dopamine systems are known to be involved in the reinforcing effects of ETOH, the role of nicotinic receptors within the nucleus accumbens (NAc) in ETOH reinforcement has not been studied. To address this issue, adult male Long-Evans rats were initiated to self-administer ETOH (10% v/v, n = 14) using the sucrose-substitution procedure or sucrose (5% w/v, n = 8) in a 30-min operant session. They were then surgically implanted with bilateral stainless-steel guide cannulae to allow for microinjection into the core of the NAc. After recovery from surgery, presession microinjections of NIC (0.3, 3.3, 10, 30, and 60 microg/1 microl/brain) or the antagonist mecamylamine (MEC) (1, 3, 10, 30, and 60 microg/1 microl/brain) were performed prior to an ETOH or sucrose self-administration session. NIC (3.3 and 60 microg/microl) and MEC (30 microg/microl) both reduced ETOH self-administration behavior, without affecting sucrose-reinforced behavior. A reduction in the total duration of ETOH responding (termination) was also observed after either 60 microg/microl of NIC and 30 microg/microl of MEC. The lack of a clear dose-response relationship for the agonist and the antagonist indicates that the interaction between the NAc nicotinic system and ETOH self-administration is complex.

Effects of bromocriptine on self-administration of sweetened ethanol solutions in rats

The effect of bromocriptine (BRO), a D2 receptor agonist, on chronic oral ethanol (ETOH) self-administration was tested in a home-cage environment. Male Wistar rats (n = 77) were food deprived for 24 h. Then, a period of 15 days of limited-access (1 h/day) to food and to a sweetened ETOH solution was started [3% w/v of glucose and several concentrations of ETOH depending upon the group: 0% (control group). 1.5%, 5% or 10% v/v]. Later, another period started in which rats were maintained in a free-choice, two-bottle situation with food, tap-water and the sweetened solution available for 24 h/day, for 14 days. Following this period, BRO (5 mg/kg, SC) was administered, once daily, for 5 days, in the same continuous free-access conditions. ETOH consumption was also studied for 4 days after the last BRO injection. BRO increased ETOH self-administration throughout the 5-day period, regardless of the ETOH concentration available, in the rats with previous higher ETOH intake, without effect in the control animals. In the control rats, water intake was increased, whereas in the group that had access to the lowest ETOH concentration a decrease in water consumption was found. The enhanced ETOH drinking was maintained after BRO treatment for the animals with previous higher ETOH intake. BRO effects on water consumption were also maintained. These data suggest that BRO can potentiate ETOH intake and provide further support for the role of dopamine (DA) systems in mediating volitional oral intake of ETOH.