Effects of agonists and antagonists at the GABA/benzodiazepine receptor on conditioned suppression in rats

Effects of early and late treatment with L-baclofen on the development and maintenance of tinnitus caused by acoustic trauma in rats

Subjective tinnitus is a chronic neurological disorder in which phantom sounds are perceived. Recent evidence supports the hypothesis that tinnitus is related to neuronal hyperactivity in auditory brain regions, and consequently drugs that increase GABAergic neurotransmission in the CNS, such as the GABA(B) receptor agonist L-baclofen, may be effective as a treatment. The aim of this study was to investigate the effects of early (5 mg/kg s.c., 30 min and then every 24 h for 5 days following noise exposure) and late treatment (3 mg/kg/day s.c. for 4.5 weeks starting at 17.5 weeks following noise exposure) with l-baclofen on the psychophysical attributes of tinnitus in a conditioned lick suppression model following acoustic trauma in rats. Acoustic trauma (a 16-kHz, 115-dB pure tone presented unilaterally for 1h) resulted in a significant decrease in the suppression ratio (SR) compared to sham controls in response to 20-kHz tones at 2, 10 and 17.5 weeks post-exposure (P ≤ 0.009, P ≤ 0.02 and P ≤ 0.03, respectively). However, l-baclofen failed to prevent the development of tinnitus when administered during the first 5 days following the acoustic trauma and also failed to reverse it when treatment was carried out every day for 4.5 weeks. We also found that treatment with L-baclofen did not alter the expression of the GABA(B)-R2 subunit in the cochlear nucleus of noise-exposed animals.

Picrotoxin blocks the anxiolytic- and panicolytic-like effects of sodium valproate in the rat elevated T-maze

The effect of acute sodium valproate administration, an anxiolytic and putative panicolytic drug, was evaluated in rats tested in the elevated T-maze, an animal model that measures two defensive reactions: avoidance (inhibitory avoidance), related to generalized anxiety, and escape (escape from open arms), related to panic. Additionally, the involvement of gamma-aminobutyric acid (GABA) neurotransmission in sodium valproate effects was studied by picrotoxin co-administration. Sodium valproate (300 mg/kg, intraperitoneally, 30 min before the test) impaired both avoidance latency (time to leave the closed arm) and one-way escape (latency to enter the closed arm) indicating anxiolytic and panicolytic effects, respectively. Pre-treatment with picrotoxin (0.5 mg/kg, intraperitoneally, 5 min before sodium valproate administration) blocked the effects of sodium valproate on inhibitory avoidance and one-way escape. No locomotor effect was seen in the open-field. These data suggest that sodium valproate exerts anxiolytic-like and panicolytic-like effects in the elevated T-maze and that these effects were mediated by picrotoxin-sensitive GABA type A receptors.

A preliminary, controlled investigation of magnesium L-aspartate hydrochloride for illicit cocaine and opiate use in methadone-maintained patients

Based on pre-clinical studies suggesting that magnesium (Mg) reduces cocaine self-administration and potentiates the antinociceptive effects of morphine, we conducted a preliminary randomized clinical trial investigating Mg for the treatment of illicit cocaine and opiate use. Eighteen methadone-maintained patients who used illicit opiates and cocaine received either Mg (732 mg/day) or placebo for 12 weeks. Overall, findings showed that the percentage of urine screens testing positive for opiates in the Mg group (22.6%) was half that of the placebo group (46.4%), p = .04; the difference was even greater in the "medication compliant" sample (Mg: 16.3%, placebo: 47.9%), p = .02. Cocaine craving was lower in the Mg compared to the placebo group, but there was no difference between groups in cocaine use. These preliminary findings suggest that Mg may have a beneficial effect for reducing illicit opiate use. It is possible that a higher dose of Mg than was used in this study may be needed to decrease cocaine use.

Ability of baclofen in reducing alcohol intake and withdrawal severity: I--Preclinical evidence

BACKGROUND

The similarities between the pharmacological effects of the gamma-aminobutyric acid receptor agonist, baclofen, and the alcohol-substituting agent, gamma-hydroxybutyric acid, led us to investigate whether baclofen was capable of reducing (a) ethanol withdrawal syndrome in ethanol-dependent rats and (b) voluntary ethanol intake in ethanol-preferring rats.

METHODS

In experiment 1, Wistar rats were rendered physically dependent on ethanol by the repeated administration of intoxicating doses of ethanol for 6 consecutive days. Baclofen was acutely administered intraperitoneally at doses of 10, 20, and 40 mg/kg. In experiment 2, baclofen (0, 2.5, 5, and 10 mg/kg, intraperitoneally) was administered once a day for 14 consecutive days to ethanol-preferring sP rats that had continuous access to ethanol (10%, v/v) and water under the two-bottle free choice regimen.

RESULTS

In experiment 1, baclofen dose-dependently decreased the intensity of ethanol withdrawal signs; furthermore, 20 mg/kg of baclofen protected from audiogenic seizures in ethanol-withdrawn rats. In experiment 2, baclofen selectively and dose-dependently reduced voluntary ethanol intake; a compensatory increase in water intake left total fluid intake virtually unchanged.

CONCLUSIONS

These results are in close agreement with those of a preliminary clinical study and suggest that baclofen may constitute a novel therapeutic agent for alcoholism.

Direct evidence for mediation of an anticonflict effect of baclofen by GABAb receptors

The present article reports an experiment on the effects of baclofen (0, 0.5, 1.0, and 2.0 mg/kg) on punished drinking in rats and the modification of these by delta-amino-n-valeric acid (DANVA) (0 and 10.0 mg/kg). Baclofen significantly enhanced punished drinking and this increase was abolished by DANVA, which had no intrinsic anxiogenic activity. It is concluded that GABAb receptors probably mediate this effect of baclofen and that such receptors may be a potential site of anxiolytic drug action.

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

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

Effects of chlordiazepoxide and putative anxiogenics on conditioned suppression in rats

This paper reports two experiments. In Experiment 1, the effects of chlordiazepoxide alone and in combination with a series of putative antagonists at various sites on the GABA/benzodiazepine receptor complex on conditioned suppression of operant behavior in rats were assessed. Response rates during presentation of a stimulus associated with shock (CS responding) and when only positive reinforcement is effective (pre-CS responding) were analysed. Chlordiazepoxide (10 mg/kg) significantly increased CS responding. This effect was significantly antagonised by Ro15-1788 (10 mg/kg) and by picrotoxin (1.5 mg/kg), but not by bicuculline (1.5 mg/kg) or by delta-amino-n-valeric acid (10 or 20 mg/kg). Chlordiazepoxide also significantly, albeit more slightly, increased pre-CS responding and none of the other drugs tested significantly antagonised this action, though Ro15-1788 plus chlordiazepoxide resulted in pre-CS response rates not significantly different from either chlordiazepoxide alone or control. These interactions are discussed in the context of the proposed GABA/benzodiazepine receptor complex with the conclusion that drug effects at the benzodiazepine- and picrotoxin-sensitive channel sites have an important role in mediating anxiolytic action. However, behavioral evidence of an important role for GABAa or GABAb receptors remains very limited. The second experiment studied the intrinsic actions of bicuculline, picrotoxin, and Ro15-1788 on conditioned suppression. Responding during a conditioned stimulus associated with a mild (0.125 to 0.15 mA) electric shock (CS responding) and a control rate of responding (pre-CS responding) were recorded. Bicuculline (1.5 mg/kg) and Ro15-1788 (10 mg/kg) did not significantly affect either response rate.(ABSTRACT TRUNCATED AT 250 WORDS)

GABAmimetic agents display anxiolytic-like effects in the social interaction and elevated plus maze procedures

Benzodiazepine (BZD) anxiolytics, through their activation of the BZD-GABA receptor complex, display robust anxiolytic-like effects following systemic administration in both conditioned and non-conditioned behavioral procedures. The present results show that the GABAA agonists muscimol (0.5-1.0 mg/kg), THIP (2.5-10.0 mg/kg), and isoguvacine (25.0 mg/kg) as well as the GABA transaminase (GABA-T) inhibitor AOAA (aminooxyacetic acid; 5.0-20.0 mg/kg) following intraperitoneal administration exert anxiolytic-like activity of similar magnitude to that of diazepam in two non-conditioned procedures, namely the social interaction and the elevated plus maze tests. We have also extended our original findings that the anti-epileptic drug sodium valproate exerts an anxiolytic-like effect in the Geller conflict paradigm, to show this agent's robust activity in the social interaction and elevated plus maze tests following systemic administration (100-400 mg/kg). These results show that GABAergic agents that facilitate GABA transmission are effective following systemic administration in non-conditioned anxiety procedures and may indicate potential therapeutic efficacy in certain anxiety states.