Interaction of GABA mimetics with nigro-striatal dopamine neurons

Perinatal maternal exposure to picrotoxin: Effects on sexual behavior in female rat offspring

A previous study in our laboratory showed that perinatal maternal picrotoxin exposure (0.75 mg/kg) in rats improved heterosexual behavior in male offspring. In the present study, we examined the effects of this maternal treatment on sexual behavior in the female offspring. The dams received 0.75 mg/kg picrotoxin treatment (PT) once a day on the 18th and 21st day of pregnancy, 2 h after parturition and once a day during the first 4 days of lactation. The results showed that (1) at birth, the body weight and anogenital distance were not modified by treatment; (2) female sexual behavior was improved in experimental animals. These results demonstrate that perinatal picrotoxin exposure improves adult sexual behavior in female rat offspring as suggested by increase in the lordosis quotient.

Inhibitory effect of GABAergic drugs in cocaine-induced genital reflexes in paradoxical sleep-deprived male rats

The aim of this study was to seek whether GABAergic drugs were involved in the action of cocaine on spontaneous genital reflexes (penile erection-PE, and ejaculation-EJ) of paradoxical sleep-deprived (PSD) male rats. After a 4-day period of PSD, each group was administered with GABAergic drugs 1 h prior to cocaine and placed in observation cages. The administration of gamma-aminobutyric acid (GABA)-A agonist (muscimol, 2 and 3 mg/kg sc) reduced the number of animals displaying PE, whereas all doses tested of muscimol and bicuculline significantly reduced the frequency of PE. Pretreatment with the lower doses of GABA-B antagonist, phaclofen (1 and 2 mg/kg sc), also significantly reduced the percentage of rats showing PE; however, after the higher dose injection, the proportion of animals with PE was similar to those seen after vehicle pretreatment. Both GABA-B agonist and antagonist significantly reduced the PE frequency for all doses used compared with the vehicle group. There were no significant differences between control and GABA-A drugs in EJ behavior, whereas phaclofen 2 mg/kg pretreatment increased the ejaculatory latency. These data show that GABAergic compounds inhibited PE in male PSD rats suggesting that this inhibition points to a differential role of GABA receptor subtypes.

Effects of perinatal picrotoxin and sexual experience on heterosexual and homosexual behavior in male rats

The effects of perinatal picrotoxin (0.75 mg/kg) on heterosexual and homosexual behavior of male rats, sexually experienced or not, were studied. The following data were obtained: (1) at birth, body weight and anogenital distance were not modified by the treatment; (2) during lactation, both treatment and sex interfered with body weight as well as in adult age; (3) as experimental animals were trained, the heterosexual behavior was improved; (4) picrotoxin treatment reduced lordotic response of homosexual behavior in inexperienced male rats and (5) the heterosexual experience with female rats inhibited homosexual behavior of both experimental and control animals. These results suggest that perinatal maternal picrotoxin exposure improved heterosexual behavior in male rats and the sexual experience reveals this effect. In addition, picrotoxin did not induce feminization in experimental inexperienced rats. Finally, the sexual experience per se promotes changes in brain regions related to male behavioral and sexual aspects.

GABAergic drugs inhibit amphetamine-induced distractibility in the rat

Drugs facilitating GABAergic neurotransmission have been reported to block some behavioral actions of dopaminergic stimulation but not others. The present experiments were performed with the purpose to extend the range of behaviors in which the interaction between GABA and dopamine have been studied. The ability of the GABAB agonist baclofen and the GABA transaminase inhibitor sodium valproate to block the enhanced distractibility produced by amphetamine was evaluated in a procedure especially designed for analyzing drugs' effects on distractibility. Briefly, rats were trained to traverse a straight runway with a sucrose solution as reinforcement. Once the response had been acquired, an additional runway ending in an empty box was connected. The time spent investigating this additional runway is the measure of distractibility. Male rats treated with amphetamine, 1 mg/kg, displayed an increase of the time spent in the additional runway. Baclofen, 2.5 and 5 mg/kg, and sodium valproate, 100 and 200 mg/kg, had no effect on distraction behavior when administered alone. However, when these drugs were administered together with amphetamine, 1 mg/kg, they completely inhibited the effects of the stimulant on distractibility. These data show that distractibility is similar to discrimination learning with regard to the capacity of GABAergic drugs to block the effects of dopaminergic stimulation. It is different from locomotor activity, however, where GABAergic drugs are ineffective in this respect.

Effects of inhibition of GABA catabolism by aminooxyacetic acid on enkephalinergic neurons--immunocytochemical and ultrastructural study in the enkephalinergic hypothalamoseptal tract of the guinea-pig

The immunocytochemical and ultrastructural features within [Met]enkephalin neurons of the guinea-pig hypothalamoseptal tract were investigated under chronic inhibition of GABAergic catabolism. This was achieved by raising the brain GABA concentration with aminooxyacetic acid which inhibits GABA-transaminase, the enzyme responsible for the catabolism of GABA. Guinea-pigs were injected intraperitoneally with 10 or 20 mg/kg per day aminooxyacetic acid for two, four or eight days and killed 16 h post-dose. Repeated injections of aminooxyacetic acid produced a great increase in immunoreactivity for GABA in nerve endings surrounding enkephalinergic perikarya in the magnocellular dorsal nucleus of the guinea-pig. Extensive immunocytochemical studies stressed the increase and redistribution of the immunoreaction for [Met]enkephalin in the perikarya of the magnocellular dorsal nucleus under such GABAergic activation. Quantitative and statistical analyses showed that administration of aminooxyacetic acid for eight days significantly increased the intensity of labelling within stimulated perikarya (P less than 0.001). A concomitant accumulation of immunopositive large granules in the enkephalinergic boutons of the lateral septum was observed. In the same way, ultrastructural changes in enkephalinergic cell bodies were analysed and reflected disturbances in the biosynthetic and digestive activities of enkephalinergic perikarya. We postulate that chronic inhibition of the GABAergic catabolism leads to modification in the metabolism of enkephalinergic neurons and to an inhibitory action of GABA on the [Met]enkephalin release from nerve endings. This study give morphological support to the complex functional interactions between GABA and opioid peptide transmitter system.

Effects of etybenzatropine and diazepam on levodopa-induced diphasic dyskinesias in Parkinson's disease

Levodopa-induced onset and end-of-dose dyskinesia are rare but disabling disorders. Although they can be attenuated by increasing and dividing the daily dose of levodopa, this does not constitute a therapeutic approach. In this pilot study, etybenzatropine, an anticholinergic drug, and diazepam, a selective benzodiazepine, were administered in addition to a single dose of levodopa in nine patients with Parkinson's disease. Both drugs tended to decrease the severity and the duration of onset and end-of-dose dyskinesia and to increase the duration of action of levodopa on parkinsonian symptoms.

Effects of acute and subacute administration of bicuculline on dopamine and muscarinic receptors in rat brain

The changes of characteristics of dopamine (D1 and D2) and muscarinic receptors after acute and subacute administration of bicuculline were examined in rat brain. The results demonstrated that in striatal region, the Bmax of D2 receptor was significantly increased with no change of affinity after subacute administration of bicuculline. However, neither Bmax nor Kd or the D2 receptor was changed after single administration. The characteristics of D1 receptor were not changed by either acute or subacute administration. The Bmax of muscarinic receptor in striatal area was significantly increased without changes of affinity after both a single and repeated administration of bicuculline. However, in hippocampus, the Bmax of muscarinic receptor was significantly decreased after subacute administration of bicuculline. The results suggest that the interactions among GABAergic, dopaminergic and cholinergic neuron exist in central nerve system.

GABA and dopamine interaction in the basal ganglia: dopaminergic supersensitivity following chronic elevation of brain gamma-aminobutyric acid levels

The influence of chronic activation of the gamma-aminobutyric acid (GABA) system on dopaminergic function was evaluated in male rats. Activation of the GABA system was achieved by raising the brain concentration of GABA with aminooxyacetic acid (AOAA), a GABA-transaminase (GABA-T) inhibitor. Repeated i.p. injection (40 or 80 mg/kg/day for 8 days) of AOAA produced a sustained elevation of GABA concentration in the striatum. Beginning 26 h following the last dose of a regimen of AOAA treatment (80 mg/kg/day for 8 days), the animals exhibited a characteristic spontaneous 'sham-fighting' behavioral stereotypy which peaked at 34 h after the last dose of AOAA; this spontaneous behavior dissipated by 38 h postdose. When challenged with apomorphine, the sham-fighting behavior was interspersed with intense fighting episodes; these precipitated behaviors were evident for up to 2 weeks posttreatment observation period. Animals given a lower dose of AOAA (40 mg/kg/day X 8) did not show signs of spontaneous sham-fighting, but responded with fighting upon apomorphine challenge. Qualitatively similar behavioral effects were obtained when gamma-acetylenic GABA (30 mg/kg/day, i.p. for 8 days) was used as the inhibitor of GABA-T. Measurement of dopamine and its acid metabolites in the striatum showed an enhanced turnover of dopamine during the spontaneous behavioral response, suggesting a rebound phenomenon. The levels of 5-hydroxytryptamine or its acid metabolite or neuroactive amino acids such as glutamate, aspartate, taurine, glycine, glutamine in the striatum were not altered by any of the treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between naloxone and GABA in the control of locomotor activity in the rat

It was found that naloxone causes a small but significant reduction of motility. The GABAB agonist baclofen and the GABA transaminase inhibitor gamma-acetylenic GABA (GAG) also reduced locomotor activity. When a subeffective dose of baclofen was combined with naloxone 0.8 or 3.2 mg/kg, baclofen significantly inhibited motility beyond the inhibition caused by naloxone + saline. GAG, in a dose of 12.5 mg/kg, was also potentiated by naloxone, 3.2 mg/kg. The locomotion reducing effects of naloxone could be blocked by either picrotoxin or bicuculline. It is concluded that GABAergic mechanisms participate in the inhibition of locomotor activity provoked by naloxone. The possibility that this drug disinhibits GABAergic neurons is discussed.

Subchronic administration of GABAergic agonists elevates [3H]GABA binding and produces tolerance in striatal dopamine catabolism

Directly and indirectly acting GABAergic agonists were assessed for their ability to alter striatal dopamine catabolism after subchronic administration (7-14 days) via subcutaneously implanted osmotic minipumps. THIP, kojic amine and baclofen failed to alter striatal DOPAC and HVA concentrations, but THIP and kojic amine were effective after a single acute dose. Striatal GABA levels proved difficult to elevate when inhibitors of GABA transaminase were released from minipumps, but a high dose of gamma-vinyl GABA increased GABA by 44% of control, although striatal dopamine and DOPAC levels were unaltered. [3H]GABA binding studies revealed that THIP and kojic amine, but not baclofen or gamma-acetylenic GABA, produced large increases in [3H]GABA 'A' binding (150 and 228% of control respectively) which were attributable to altered densities of binding sites without changes in affinity. Despite alterations in GABAergic function, nigrostriatal dopaminergic neurones seem to develop tolerance to the effects of GABAergic drugs.

Clinical activity of GABA agonists in neuroleptic- and L-dopa-induced dyskinesia

It is well known that the therapeutic effect of neuroleptics is counterbalanced by the property of these drugs to induce serious neurological side-effects mainly represented by tardive dyskinesia. Several reports indicate that at the experimental level GABA agonists interact with dopamine neurons with effects on behavior, stereotyped and dyskinetic movements induced by either lesions or dopamine agonists. This action on dopamine-related events provides a basis for a possible therapeutic action of GABA agonists in dyskinesia. Previous results with the GABA agonists muscimol and THIP in tardive dyskinesia have not been encouraging. The present paper deals with clinical results obtained with the new GABA agonist progabide both in neuroleptic-induced dyskinesia and in L-dopa-induced dyskinesia from five studies conducted on a total of 57 patients. Twenty-nine patients suffering from neuroleptic-induced dyskinesia have been treated in three studies (two open, one double-blind cross over) with progabide at doses from 900 to 2400 mg/day; clinical evaluation and EMG testing are in favor of a therapeutic effect of progabide on dyskinesia. Twenty-eight patients with L-dopa dyskinesia have been studied in two double blind trials. At variance with studies in tardive dyskinesia progabide was not effective in this kind of dyskinesia but an increase in the "on" time has been observed in both studies. Attempts to treat tardive dyskinesia with various pharmacological tools are reviewed and discussed, showing that at present no established effective treatment exists for this frequent complication of neuroleptic use. The possible mechanism of action of progabide in dyskinesia is discussed in the light of its pharmacological properties. These results suggest that progabide can be useful in the treatment of neuroleptic-induced dyskinesia.

The locomotor-reducing effects of GABAergic drugs do not depend on the GABAA receptor

The locomotion-reducing effect of the GABAB agonist baclofen was compared with that of the GABAA agonists, aminopropanesulfonic acid (APSA) and THIP. It was found that baclofen was more potent than the other drugs. After intraventricular injection, baclofen induced almost complete immobility, whereas APSA did not affect locomotor activity. THIP had an intermediate effect. The GABA transaminase inhibitor gamma-acetylenic GABA (GAG) provoked a dose-dependent reduction of locomotion. Neither the effects of THIP nor those of GAG could be blocked by concurrent administration of bicuculline. The antagonist itself did not affect locomotor activity. It is concluded that the GABAA receptor is not important for the locomotion-reducing effects of GABAergic drugs.

Induction and reversal of dopamine dyskinesia in rat, cat, and monkey

Abnormal involuntary movements (AIMs, stereotyped or dyskinetic movements) were induced with different dopamine mimetics in rat, cat, and monkey. In the rat only stereotyped movements were observed, whereas in the cat dopamine agonists (apomorphine) preferentially induced dyskinesia but dopamine/noradrenaline uptake inhibitors (d-amphetamine, nomifensine) induced predominantly stereotypes; L-dopa induced an equal, low, number of both kinds of movements in the cat. In the monkey with bilateral lesions of the nigrostriatal dopamine pathways the AIMs could be divided into type 1 dyskinesia (behavioral), type 2 dyskinesia (oral and psychomotor), and chorea. GABA agonists (progabide, muscimol) had a biphasic action on apomorphine stereotypes in the rat, slightly (10%-20%) augmenting these movements at low doses and antagonizing (greater than 50%) them at higher doses. As these latter doses of progabide also antagonize apomorphine-induced circling in rats with a unilateral lesion of the substantia nigra, it is likely that this action is exerted at or beyond the dopamine target cell. In cats the dyskinetic movements induced by apomorphine were abolished by progabide. In contrast, L-dopa-induced stereotypies were resistant to the antidyskinetic action of progabide, and at low doses of L-dopa an increased incidence of stereotypies was noted. In the monkey, the type 1 dyskinesia following L-dopa and piribedil were also relatively resistant to progabide administration, whereas the type 2 dyskinesia and chorea were abolished by progabide. These studies are parallel to and support the clinical observations that dyskinetic movements following a direct action at the dopamine receptor (tardive dyskinesia) may be reversed by progabide whereas those associated with dopamine neuron activity, perhaps together with noradrenergic activation (L-dopa dyskinesia), are resistant to the antidyskinetic action of progabide.