Anticonvulsive activity of several excitatory amino acid antagonists against barbital withdrawal-induced spontaneous convulsions

Some rewarding effects of androgens may be mediated by actions of its 5alpha-reduced metabolite 3alpha-androstanediol

The abuse of anabolic-androgenic steroids (AS) is a growing problem; however, the effects and mechanisms underlying their addictive effects are not well understood. Research findings regarding androgen abuse in people and hedonic effects of androgens in laboratory rats are reviewed. Androgens, like other steroids, can have traditional actions via cognate intracellular steroid receptors, as well as other substrates. Our recent results indicate that testosterone (T) metabolites may have actions in part via gamma-aminobutyric acid (GABA)(A)/benzodiazepine receptor complexes (GBRs) and/or dopaminergic neurons in the nucleus accumbens, to mediate T's positive hedonic states. This may provide the basis for positive reinforcing effects of androgen seeking and use behavior. Following a comprehensive review of the background literature, our findings are presented that have explored the extent to which metabolites of T mediate euphorogenic effects of androgens by acting in the nucleus accumbens. Then results regarding whether GBRs are necessary substrates for androgens' positive hedonic effects are discussed. Lastly, research that addresses if dopaminergic neurons in the nucleus accumbens are necessary for these effects of androgens are discussed. This review provides a comprehensive examination of the hedonic properties and abuse/addiction potential of androgens and the putative mechanisms underlying these effects.

Finasteride blocks the reduction in ictal activity produced by exogenous estrous cyclicity

The purpose of the present study was to examine seizure activity during reduced 5alpha-pregnan-3alpha-ol-20-one (3alpha,5alpha-THP) production. Ovariectomized Long-Evans rats were stereotaxically implanted with bipolar electrodes above the perforant pathway; silastic implants filled with estradiol-17-benzoate (EB) and progesterone were inserted subcutaneously to mimic diestrus. Estrus was then induced in half of these animals by injection of EB (30 microg) and progesterone (2.5 mg), 48 and 4 h, respectively, prior to perforant pathway stimulation. Half of the estrous and diestrous rats also received a 5alpha-reductase inhibitor, finasteride (50 mg/kg), 6 h prior to perforant pathway stimulation. The estrous condition was associated with reduced number and duration of partial seizures, improved performance on a Morris water maze recovery of function test, reduced neuronal loss in the hilar region of the hippocampus, and elevated central and plasma 3alpha,5alpha-THP, compared to estrus+finasteride, diestrus+vehicle and diestrus+finasteride conditions, which did not differ from each another. These data suggest antiseizure effects of estrus may be caused, in part, by the action of 3alpha,5alpha-THP and that the precipitous decline in 3alpha,5alpha-THP may restore seizure threshold to control levels.

Role of NMDA receptors in pentobarbital tolerance/dependence

Effects of continuous pentobarbital administration on binding characteristics of [3H]MK-801 in the rat brain were examined by autoradiography. Animals were rendered tolerant to pentobarbital using i.c.v. infusion of pentobarbital (300 micrograms/10 microliters/hr for 7 days) by osmotic minipumps and dependent by abrupt withdrawal from pentobarbital. The levels of [3H]MK-801 binding were elevated in rats 24-hr after withdrawal from pentobarbital while there were no changes except in septum and anterior ventral nuclei in tolerant rats. For assessing the role of NMDA receptor in barbiturate action, an NMDA receptor antagonist (MK-801, 2.7 femto g/10 microliters/hr) was co-infused with pentobarbital. The pentobarbital-infused group had a shorter duration of pentobarbital-induced loss of righting reflex (sleeping time) than that of the control group, and MK-801 alone did not affect the righting reflex. However, co-infusion of MK-801 blocked hyperthermia, and prolonged the onset of convulsions induced by t-butylbicyclophosphorothionate (TBPS) in pentobarbital withdrawal rats. In addition, elevated [35S]TBPS binding was significantly attenuated by co-infusion with MK-801. These results suggest the involvement of NMDA receptor up-regulation in pentobarbital withdrawal and that the development of dependence can be attenuated by the treatment of subtoxic dose of MK-801.

Excitatory amino acids and drugs of abuse: a role for N-methyl-D-aspartate receptors in drug tolerance, sensitization and physical dependence

N-methyl-D-aspartate (NMDA) receptors have been implicated in several types of neural and behavioral plasticity ranging from development to learning. The present paper reviews evidence suggesting that these receptors might also be involved in the neural and behavioral changes resulting from chronic administration of drugs of abuse. NMDA receptor antagonists have been found to interfere with tolerance, sensitization, physical dependence and conditioning to a variety of self-administered drugs, including psychomotor stimulants, opiates, ethanol and nicotine. The results indicate a broad role for NMDA receptors in drug-induced neural and behavioral plasticity, including changes in the brain and behavior that may lead to compulsive drug use, and suggest that drugs acting at the NMDA receptor complex may be clinically useful.

The WAG/Rij rat model for nonconvulsive absence epilepsy: involvement of nonNMDA receptors

The involvement of AMPA and kainate receptors in nonconvulsive epilepsy was studied by intracerebroventricular injections of AMPA, GDEE, kainic acid and kynurenic acid in WAG/Rij rats. The WAG/Rij rat strain is recognized as an animal model for human absence epilepsy. EEG registrations showed that AMPA (0.1 pmol/5 microliters; 1 pmol/5 microliters; 10 pmol/5 microliters) dose-dependently increased the nonconvulsive absence epilepsy while GDEE (0.2 mumol/5 microliters; 1 mumol/5 microliters; 5 umol/5 microliters) caused a dose-dependent decrease. All effects of GDEE could be blocked by an inactive AMPA dosage. Kainic acid (0.01 nmol/5 microliters; 0.1 nmol/5 microliters; 0.15 nmol/5 microliters) had no effects on the nonconvulsive epilepsy but induced convulsions in the two highest dosages. Kynurenic acid (50 nmol/5 microliters; 100 nmol/5 microliters; 500 nmol/5 microliters) decreased dose-dependently the incidence of nonconvulsive epilepsy. The effect of kynurenic acid could be blocked by a nonconvulsive dosage of kainic acid. These results show that the AMPA and kainate receptor appear to be involved in nonconvulsive epilepsy. Furthermore, blockage of these two receptor subtypes led to an antiepileptic effect without inducing behavioural alterations. Therefore, selective AMPA and kainate receptor antagonists might be potent anti-epileptics.

Possible involvement of NMDA receptor-mediated transmission in barbiturate physical dependence

1. The competitive antagonists at the N-methyl-D-aspartate (NMDA) receptor, CGP39551 and CGP37849, protected against the barbiturate withdrawal syndrome in mice, as measured by ratings of convulsive behaviour on handling. 2. The effective doses of these compounds were lower than those required to prevent seizures due to NMDA in naive animals; these were in turn lower than those needed to prevent the convulsive effects of the alpha-aminobutyric acid (GABA) antagonist, bicuculline. 3. The NMDA-receptor antagonists did not alter the increase in the incidence of convulsions due to the GABAA antagonist, bicuculline, that is seen during barbiturate withdrawal, although the latencies to these convulsions during barbital withdrawal were significantly increased after CGP39551. 4. Barbiturate withdrawal did not affect the convulsive actions of NMDA, whether measured by the incidence of convulsions or by intravenous infusion. 5. The Bmax for [3H]-dizocilpine ([3H]-MK801) binding was significantly increased by chronic barbital treatment in cerebrocortical but not in hippocampal tissues, while the Kd remained unaltered in either case. 6. At 1 h and 24 h after administration of a single dose of barbitone, the Bmax for [3H]-dizocilpine binding was unaltered in cerebrocortical tissue. Acute addition of barbitone in vitro did not alter [3H]-dizocilpine binding or the displacement of binding of thienylcyclohexylpyridine.

Progesterone withdrawal decreases latency to and increases duration of electrified prod burial: a possible rat model of PMS anxiety

The purpose of this study was to determine whether withdrawal from chronic exposure to the female sex steroid progesterone (P) alters response of female rats to an electrified prod using the defensive burying paradigm, considered a rat model of anxiety. Withdrawal from chronic exposure to 500 micrograms P (daily, SC, for four days) resulted in a significant decrease in the latency (77%, P < 0.05) to prod burial and an increase in duration (75%, P < 0.05) of this reflexive response, compared with the behavior of oil-injected controls. These results are consistent with the idea that withdrawal from chronic exposure to P increases behaviors that accompany anxiety. At a lower dose (50 micrograms), withdrawal from chronically administered P produced significant changes in response to this paradigm only when the steroid was given concomitantly with estradiol (2 micrograms, SC, for two days). Prior exposure to indomethacin, which blocks the conversion of P to its metabolite 3 alpha,5 alpha-tetrahydroprogesterone (3-alpha-hydroxy-5-alpha-pregnan-20-one), prevented P withdrawal from altering response in the defensive burying paradigm. This finding suggests that it may be withdrawal from this metabolite, rather than P, which increases behaviors associated with increased anxiety.

Acute, chronic and differential effects of several anesthetic barbiturates on glutamate receptor activation in neuronal culture

The acute and chronic effects of several anesthetic barbiturates, in therapeutic concentrations, on the excitatory amino acid (EAA)-induced elevation of intracellular calcium levels ([Ca2+]i) were examined in neuronal tissue culture. The ultrashort-acting barbiturate, thiamylal, was effective in blocking elevations of [Ca2+]i induced by kainate, N-methyl-D-aspartate (NMDA), and quisqualate or by membrane depolarization with 40 mM KCl. The structurally similar barbiturate, secobarbital which differs from thiamylal only by having an oxygen in place of a sulfur, was able to block elevations induced by the above EAAs but was less effective than thiamylal and did not significantly reduce [Ca2+]i that resulted from membrane depolarization with KCl. Pentobarbital, while differing from secobarbital by only a methyl group, was without effect on either the NMDA- or 40 mM KCl-induced elevations of [Ca2+]i. By contrast, cyproheptadine, a compound that has been shown to block Ca2+ channels, has a different profile from the above barbiturates in that cyproheptadine is more effective in blocking elevation of [Ca2+]i induced by membrane depolarization with KCl while the barbiturates are more effective in reducing [Ca2+]i induced by EAAs. An anticonvulsant barbiturate, phenobarbital, did not reduced elevations of [Ca2+]i induced by any EAA tested or by membrane depolarization with KCl. When cells were treated chronically with thiamylal for 4 days, 2-6 h after the abrupt drug withdrawal there was a hyperresponsiveness to the elevations of [Ca2+]i induced by both kainate and NMDA but not by quisqualate. A similar hyperresponsiveness was not seen after the chronic treatment with phenobarbital.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of neuronal calcium channels in dependence on ethanol and other sedatives/hypnotics

This review discusses the importance of neuronal calcium currents in dependence on ethanol, barbiturates, benzodiazepines and opiates. The main sections describe the actions of ethanol on control of intracellular calcium and on calcium and calcium-dependent conductance mechanisms. In particular, the effects of both acute and chronic ethanol treatment on dihydropyridine-sensitive, voltage-dependent, calcium channels are described. The later sections cover the effects of barbiturates, benzodiazepines and opiates on these systems. The conclusions suggest that dihydropyridine calcium channel antagonists may offer a new therapeutic approach to the treatment of ethanol and opiate dependence.

Biphasic action of dextrorphan on penicillin induced bursting in rat hippocampal slice

Effects of dextrorphan (DX), a metabolite of the over-the-counter antitussive, dextromethorphan, were investigated in rat hippocampal slices exposed to the epileptogenic agent penicillin. At 50 microM and 100 microM concentrations dextrorphan suppressed late components of the epileptiform CA1 field potential elicited by afferent electrical stimulation, and partially suppressed the intracellularly recorded paroxysmal depolarization shift. These effects were not due to non-specific changes in cell excitability, since resting cell membrane potential, input resistance, and the ability of cells to fire action potentials in response to direct depolarizing current were unaffected. The depressant effect of 100 microM dextrorphan was probably due to actions at the NMDA receptor, since pretreatment with the competitive NMDA antagonist D-APV prevented any further depressant effects of dextrorphan in this model. In contrast, at a 10 microM concentration DX enhanced the amplitude of evoked epileptiform field potentials and intracellularly recorded EPSPs. These findings support a role for dextrorphan and similar agents as anticonvulsants at high concentrations, but raise a caution regarding possible excitatory actions of dextrorphan at low concentrations.

Increased response of cerebellar cGMP to kainate but not NMDA or quisqualate following barbital withdrawal from dependent rats

Female Sprague-Dawley rats were maintained on a diet of powdered food containing barbital for 8 weeks before the drug was abruptly withdrawn. Twenty-four hours later both barbital-dependent and control rats were injected intracerebroventricular (i.c.v.) with saline or one of four doses of kainic acid (KA) or in a separate experiment with saline or one of three doses of N-methyl-D-aspartic acid (NMDA) or of quisqualic acid (QA). After 4.5 min, the animals were killed by focused microwave irradiation, and the cerebella were collected. The levels of cyclic guanosine 3',5' monophosphate (cGMP) were markedly elevated in the cerebella of barbital-withdrawn rats when compared to controls. When compared to saline treatment, KA, at all dosages, resulted in a significantly greater elevation of cerebellar cGMP in the barbital-withdrawn rats than was induced by drug withdrawal alone. Only the two higher dosages of KA produced a significant elevation of this parameter in the control rats. Unlike KA, neither QA or NMDA produced any greater elevations of cGMP in barbital withdrawn rats than were induced by drug withdrawal alone. These collective results suggest that there is an increase in the response to KA but not QA or NMDA following the withdrawal of barbital from dependent rats.