The effects of diazepam on brain 5-HT and 5-HIAA in stressed and unstressed rats

Regulation of corticosteroid receptors in the rat brain: the role of serotonin and stress

It has been suggested that physiological resistance to repeated stress is associated with increased 5-hydroxytryptamine (5-HT) release in the dorsal hippocampus and that dysregulation of this neuroadaptation may be implicated in the psychopathology of depression. This study used 5,7-dihydroxytryptamine lesions to investigate the role of 5-HT projections to the hippocampus in physiological responses to repeated stress and putative changes in corticosteroid receptor immunoreactivity in the brain. Repeated exposure to elevated open platform stress (1 h/day) caused regionally selective changes in glucocorticoid and mineralocorticoid receptor immunoreactivity in the dorsal hippocampus that were not observed in ventral hippocampus, frontal cortex, hypothalamus or parietal cortex. Glucocorticoid receptor immunoreactivity in the dorsal hippocampus was decreased after 5 days but increased after 20 days of stress. Mineralocorticoid receptor immunoreactivity was increased after 5 or 10 days of stress. The increases in glucocorticoid and mineralocorticoid receptor immunoreactivity, evoked by repeated stress, were abolished by lesions of the principal 5-HT projections to the hippocampus. The lesions abolished the increased defecation observed in stressed animals, but had no effects on the plasma corticosterone response to the stressor or the habituation of this response observed following repeated stress. The experiments have revealed a dissociation in the regulation of corticosteroid receptor expression in the dorsal and ventral hippocampus by repeated stress and 5-HT. The data suggest that adaptation to inescapable stress is associated with regionally selective changes in corticosteroid receptor expression in dorsal hippocampus that are largely 5-HT-dependent, although these changes do not mediate habituation of the pituitary adrenocortical response to the stressor.

Enhanced evoked responses after early adversity and repeated platform exposure: the neurobiology of vulnerability?

BACKGROUND

There is a long-standing clinical awareness of the significance of adverse early experiences and subsequent stress in the evolution of psychiatric disorder.

METHODS

We investigated the impact of a single episode of preweaning maternal separation on in vivo electrophysiologic responses in the hippocampus of the mature rat after repeated exposure to an open elevated platform.

RESULTS

Only rats that had experienced both maternal separation followed by stressful platform exposure when mature had significantly increased granule cell response to perforant path stimulation, compared with control rats. Rats exposed to either maternal separation or the elevated platform in adulthood alone did not differ significantly from control rats.

CONCLUSIONS

Adverse early experience seems to induce functional changes in the hippocampus that remain latent until activated by stress in adulthood. Such electrophysiologic changes might represent a neural substrate for vulnerability to stress-associated psychopathology.

The effects of nicotine on neural pathways implicated in depression: a factor in nicotine addiction?

The prevalence of tobacco smoking varies considerably between different groups within the community, tobacco smoking being particularly prevalent in patients with depressive disorder. This review will focus on results, derived from animal studies, which suggest that, in addition to its primary reinforcing properties, nicotine also exerts effects in stressful environments, which may account for its enhanced addictive potential in depressed patients. It focuses on the evidence that depression sensitises patients to the adverse effects of stressful stimuli, and that this can be relieved by drugs that stimulate dopamine release in the forebrain. This mechanism, it is proposed, contributes to the increased craving to smoke in abstinent smokers exposed to such stimuli, because they become conditioned to use this property of nicotine to produce rapid alleviation of the adverse effects of the stress. The review also explores the possibility that chronic exposure to nicotine elicits changes in 5-HT formation and release in the hippocampus which are depressogenic. It is postulated that smokers are protected from the consequences of these changes, while they continue to smoke, by the antidepressant properties of nicotine. However, they contribute to the symptoms of depression experienced by many smokers when they first quit the habit.

Pharmacology of nicotine and its therapeutic use in smoking cessation and neurodegenerative disorders

During the last decade, nicotine has been used increasingly as an aid to smoking cessation and has been found to be a safe and efficacious treatment for the symptoms of nicotine withdrawal. This period has also seen significant advances in our understanding of the mechanisms underlying the psychopharmacological responses to nicotine, including, particularly, those that have been implicated in nicotine addiction. This paper reviews this decade of progress in the specific context of the therapeutic application of nicotine to the treatment of smoking cessation. Other putative future applications, particularly in the treatment of neurodegenerative disorders, are also reviewed.

Diazepam withdrawal: effects of diazepam and gepirone on acoustic startle-induced 22 kHz ultrasonic vocalizations

It has proven difficult to demonstrate and study the "anxiogenic" quality of drug withdrawal states in animals. Ultrasonic vocalizations (USV) in response to acoustic startle stimuli have shown promise as a measure of affect and may represent "distress" responses during diazepam withdrawal. Three experiments evaluated the association between USV and "distress" by comparing the effects of diazepam as a prototypic benzodiazepine agonist and the putative anxiolytic gepirone with affinity for 5-hydroxytryptamine (5-HT1A) receptors in naive and diazepam-withdrawn subjects. Adult male Long-Evans rats were exposed to acoustic startle sessions consisting of nine 105 dB and nine 115 dB stimuli. USV at 20-30 kHz were readily emitted during startle and often commenced after the third or fourth stimulus presentation. Acutely, intraperitoneal (IP) administration of diazepam (0.1-3 mg/kg) and gepirone (0.1-1 mg/kg) decreased USV dose-dependently without affecting the startle reflex; gepirone also decreased tail flick latency. Startle-induced USV were also sensitive to the "anxiogenic" effects of withdrawal from diazepam exposure (0, 2.5, 5, 10 mg/kg b.i.d. IP x 5 days). Twenty-four hours after the last diazepam injection, rats were hyperreactive to startle stimuli and doubled their rate of USV over vehicle-treated controls. Gepirone (0.1-1 mg/kg IP), but not diazepam (3-20 mg/kg IP) antagonized the increased rate of USV in rats withdrawn from 10 mg/kg b.i.d. diazepam. Diazepam (2.5-10 mg/kg IP) antagonized the increased rate of USV in rats withdrawn from 2.5 mg/kg b.i.d. diazepam.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevention of learned helplessness: in vivo correlation with cortical serotonin

Learned helplessness (LH) is prevented by pretreatment with acute benzodiazepines (BDZs), subchronic tricyclic antidepressants (TCAs), or escapable stress (ES). We have investigated the role of serotonin (5-HT) in LH prevention by these three prevention paradigms, using microdialysis to measure in vivo 5-HT release in frontal cortex (FC) after LH testing. Rats receiving pretreatment before inescapable stress with any of the three methods of prevention--BDZs, TCAs, or ES--showed escape behavior in the shuttle-box test for LH comparable to naive unstressed controls. K(+)-stimulated 5-HT release in all three groups receiving pretreatment was also similar to naive unstressed controls. Rats receiving saline before inescapable stress showed significantly more LH behavior in the shuttle-box task and had significantly lower 5-HT release as well. This suggests that LH correlates with a significant decrease in intracellular releasable 5-HT in FC, and that three different techniques for LH prevention, acute BDZs, subchronic TCAs, and ES all similarly prevent this 5-HT depletion.

Region-selective reduction of brain serotonin turnover rate and serotonin agonist-induced behavior in mice treated with clonazepam

Evidence supports a complex interaction between benzodiazepines and the central serotonergic system. This study attempts to correlate biochemical changes in the serotonin (5HT) system induced by clonazepam (CLON) with the behavioural response to a 5HT agonist. The acute administration of CLON to mice produced a time-dependent decrease in 5HT turnover rate in the raphe area (dorsal and medial raphe nuclei) and modified the serotonergic syndrome induced by 5-methoxy-N,N,-dimethyltryptamine (DMT). One hour after CLON administration, a dose-dependent increase in 5HT concentration was found in the raphe area, while 5-hydroxyindoleacetic acid (5HIAA) levels remained stable, leading to an increase in 5HT/5HIAA ratio, indicative of reduced 5HT turnover rate. No significant changes were detected in the frontal cortex of CLON-treated mice. After 4 days of CLON treatment, the 5HT turnover rate was still decreased in the raphe area and unchanged in the frontal cortex. Acute CLON administration produced dose-dependent alterations in locomotor activity, not observed after subchronic administration. Lateral head weaving, a motor manifestation of the serotonergic syndrome produced by DMT, was less intense in CLON-treated animals. The modifications in the 5HT system induced by CLON are region selective, suggesting differences in the receptors implicated in the interaction. Altered synaptic availability of 5HT as a result of CLON administration may be responsible for the differential response to DMT in control and CLON-treated mice.

Effects of buspirone and chlordiazepoxide on plasma catecholamine and corticosterone levels in stressed and nonstressed rats

The effects of intragastric administration of the prototypical benzodiazepine (BDZ) anxiolytic drug chlordiazepoxide (CDP) and the non-BDZ anxiolytic agent buspirone (BUSP) on basal and stress-elevated plasma noradrenaline (NA), adrenaline (A) and corticosterone (CS) contents were investigated. Acute dosing of CDP (1-27 mg/kg) produced dose-related increases in basal CS secretion but was without effect on basal NA levels. The high dose of CDP caused a slight short-term A increase. Dose-dependent increases in plasma A, NA and CS contents were observed after acute treatment with BUSP (2 and 20 mg/kg). A medium dose of CDP (9 mg/kg) attenuated the stress-induced CS and A elevations. High doses of CDP that elevated basal CS release prevented a further increase of CS by stress and inhibited the NA and A response to stress. BUSP (2 and 20 mg/kg) was not effective in decreasing the stress-elicited rise of CS, NA or A. Conversely, the 20 mg/kg dose of BUSP enhanced the stress-induced A response. Repeated administration of CDP (9 mg/kg/day for six days) produced tolerance to the elevation of basal CS triggered by acute CDP treatment, but increased the efficacy of the drug's CS and A attenuating action in stressed rats. Repeated administration of BUSP (2 mg/kg/day for six days) also produced tolerance to the acute BUSP-induced effect on basal CS release, but did not affect the stress-induced CS, NA and A responses. It is concluded that the clinically effective anxiolytic BUSP does not have the BDZ-like property to inhibit stress-induced elevations in CS, NA and A. Furthermore, the present data support other evidence that activation of 5-HT1A receptor mechanisms increases plasma catecholamine and corticosterone concentrations.

The history of benzodiazepine dependence: a review of animal studies

This article provides a historical review of the animal literature relating to the development of tolerance to the behavioral effects of benzodiazepines, and the incidence of biochemical and behavioral changes that result from termination of benzodiazepine treatment (spontaneous withdrawal responses). It charts the slow emergence of a pertinent animal literature and highlights conclusions that were prevalent in 1963 (at the introduction of diazepam), 1973 (at the introduction of lorazepam), 1980 and the present day. For 25 years the animal literature has lagged behind the clinical literature, but recent studies into the neurochemical mechanisms of benzodiazepine dependence and possible treatments for withdrawal responses suggest that, at last, animal experiments may be about to make a substantial contribution.

Effect of neurotransmitters on the system that transports Tyr-MIF-1 and the enkephalins across the blood-brain barrier: a dominant role for serotonin

Neurotransmitters and neuropeptides interact in several ways. We studied a new type of interaction: the effect of neurotransmitters on the saturable system that transports Tyr-MIF-1 and the enkephalins out of the central nervous system (CNS). The neurotransmitters were introduced into the lateral ventricle of the brain with radioiodinated peptide, using an established method previously shown to accurately quantify the amount of peptide being transported from the CNS to the blood. Serotonin inhibited transport, histamine stimulated transport, and dopamine, acetylcholine, epinephrine, GABA, kainic acid, cAMP and cGMP were without effect. Cyproheptadine, a serotonin antagonist, stimulated transport. Of several psychotropic agents tested, only tranylcypromine had a statistically significant effect and stimulated transport. Of the serotonin receptor specific agents tested, those with 5HT1 activity most consistently affected transport. We conclude that serotonin, and perhaps histamine, are important modulators of the system that transports Tyr-MIF-1 and the enkephalins out of the CNS.