A dual role for GABA in quasi-morphine abstinence behavior induced by di-n-propylacetate involving both initiation and termination

Dissimilar effects of lithium and valproic acid on GABA and glutamine concentrations in rat cerebrospinal fluid

1. This study compared the effects of the antimanic drugs, lithium and valproic acid, on GABA and glutamine CSF concentration and on head-shakes during hyponatremia. 2. Hyponatremic and normonatremic rats were treated with 2 mEq/kg lithium and 360 mg/kg valproic acid. Behavioral observation was conducted for 120 min after which blood and CSF collection were performed under anesthesia. 3. Peritoneal dialysis with glucose induced moderate hyponatremia and doubled glutamine CSF concentrations. Both lithium and valproic acid significantly increased GABA CSF levels in normonatremic and hyponatremic animals. Valproic acid induced head-shakes and increased CSF glutamine concentration. 4. The results suggest that both antimanic drugs have similar effects on GABA, but lithium is preferred if the increase in glutamine concentration poses a problem, either in the presence or absence of hyponatremia.

Lithium and valproate combined administration: acute behavioural effects and drug plasma levels

Drug plasma concentrations and behavioural effects of acute combined administration of lithium and valproic acid were studied in normonatraemic and hyponatraemic rats. Hyponatraemia was induced two hours before drug administration and behavioural observations lasted for two additional hours. Blood was collected by the end of the behavioural observation. The higher doses of valproic acid (360 mg/kg) or lithium (2 mEq/kg) induced more head-shakes and higher plasma concentration than 180 mg/kg of valproic acid or lithium 1 mEq/kg, respectively. Valproic acid and lithium administered separately induced more head shakes and higher drug plasma levels in hyponatraemic rats than in normonatraemic animals. Combined administration of valproic acid (180 mg/kg) and lithium (2 mEq/kg) produced a supra-aditive effect in head-shakes. The drug interaction between lithium and valproic acid induced a decrease in valproic acid plasma level and an increase in lithium plasma levels.

Valproic acid-induced rapid changes of met-enkephalin levels in rat brain. Probable association with abstinence behavior and anticonvulsant activity

Valproic acid (VPA) induces abstinence behavior and analgesia and displays an anticonvulsant effect, but its exact mechanism of action is not yet clear. In order to view whether proenkephalin derived-peptides are involved in the mechanism of VPA-induced behavior, we analyzed immunoreactive-met-enkephalin (IR-ME) in rat striatum, midbrain, and amygdala 10, 20, and 45 min after i.p. injection of 200 mg/kg of VPA. VPA induced body shakes that peaked within 5 to 10 min. IR-ME increased in the striatum and decreased in the midbrain at 10, 20, and 45 min, reaching the highest and lowest levels at 10 and 20 min, respectively. No changes occurred in the amygdala. Gel filtration chromatography followed by HPLC of striatum extracts showed that the increased IR-ME levels corresponded to low molecular weight peptides, including ME. These results indicate that VPA produced rapid changes of IR-ME levels in rat brain and suggest peptide participation in the mechanisms of VPA-induced behavior. The anticonvulsant effect of VPA was tested in rats treated with pentylenetetrazol (70 mg/kg) 30 min after VPA (400 mg/kg) administration, and IR-ME was analyzed in striatum 15 min later. No changes in striatal IR-ME levels occurred in protected rats (no behavioral convulsions), compared with those treated only with VPA, but a significant decrease appeared in unprotected animals (clonic convulsions). These results suggest that striatal ME may participate in the mechanism of VPA-induced abstinence behavior and in the anticonvulsant effect. Otherwise, midbrain ME might be involved in other VPA behaviors such as analgesia.

Paradoxical role of GABA in a chronic model of petit mal (absence)-like epilepsy in the rat

Neonatal Long-Evans hooded rats were treated with AY-9944, a cholesterol biosynthesis inhibitor, every 6 days for 7 weeks to induce a permanent absence-like epileptic condition. AY-9944-treated rats averaged 50 +/- 15 generalized non-motor seizures per hour of 2-15 s duration as monitored by electrocorticography. Clinically effective anti-absence drugs were observed to reduce seizure occurrence in a dose-dependent manner. Paradoxically, GABA agonists increased seizure occurrence while GABA antagonists decreased seizure occurrence. Evaluation of the benzodiazepines, diazepam and clonazepam, in this model revealed inhibition of seizure activity by GABA-independent mechanisms. Valproic acid produced a biphasic effect suggesting a GABA-independent, antiabsence action at low doses and GABAergic augmentation of seizure occurrence at higher doses. The results of this study support the hypothesis that increased GABAergic stimulation may induce inhibitory seizures in absence epilepsy.

Marked increase in anticonvulsant activity but decrease in wet-dog shake behaviour during short-term treatment of amygdala-kindled rats with valproic acid

The anticonvulsant activity of valproic acid (VPA) was determined in amygdala-kindled rats after single and repeated (total of 7 injections given 3 times per day) administration of 200 mg/kg i.p. After a single injection, VPA significantly reduced the severity and duration of the kindled seizures and decreased the duration of after-discharges recorded from the stimulated amygdala, but only 12% of the animals were totally protected from seizures. The percentage of animals totally protected increased to 88% after 7 doses. This pronounced increase in the anticonvulsant activity was not related to alterations in the plasma concentrations of VPA or its major active metabolites. Furthermore, determination of VPA and its metabolites in the substantia nigra after a single and repeated administration yielded the same data, again indicating that the increase in the anticonvulsant activity was not due to drug accumulation. In contrast to the marked increase in the anticonvulsant efficacy of VPA during short-term treatment, wet-dog shake behaviour induced by a single injection of the drug was significantly attenuated after repeated dosing, indicating that the anticonvulsant effect of VPA and the wet-dog shake behaviour induced by the drug were not mediated by the same mechanism. This was substantiated by experiments with one of the major metabolites of VPA in rat plasma, trans-2-en-VPA, which had approximately the same anticonvulsant efficacy as VPA but did not induce wet-dog shakes in rats.

Effects of inhibitors of GABA-transaminase on hole-board exploration and on temperature. Relation with effects on quasi-morphine abstinence behaviour induced by sodium dipropylacetate

Four inhibitors of gamma-aminobutyric acid transaminase (GABA-T) were investigated together with respect to their effects on hole-board exploration and temperature and the relation with effects on quasi-morphine-abstinence behaviour induced by dipropylacetate (DPA) in rats. Amino-oxyacetic acid (AOAA), gamma-acetylenic-GABA (GAG), gamma-vinyl-GABA (GVC) and ethanolamine-O-sulfate (EOS) were found to reduce hole-board exploration especially in the higher doses used, although the time-course of the effect was different for the compounds. For EOS and GVG the decrease in hole-board exploration paralleled a strong hypothermic effect. The compounds AOAA and GAG exerted a less and more transient hypothermic effect. However, the decrease in hole-board exploration did not fall in with this decrease in temperature. AOAA and GAG were found to decrease DPA-induced body shakes and locomotor activity, while GVG and EOS had no effect on body shakes and transient effects but opposite to each other, on locomotor activity. The efficacy of the GABA-T-inhibitors was measured biochemically, and the influence on the activity of glutamate decarboxylase (GAD) was also determined. AOAA and GAG were found to be strong inhibitors of GABA-T whereas the other two compounds were less efficient in the used doses. In addition AOAA and GAG influenced the activity of GAD strongly, while using GVG only a small decrease was found. The results suggest that the anti-quasi-withdrawal, the sedative and the hypothermic effects are not related to each other nor related to an effect on GABA-T. The suppressive effects on quasi-withdrawal body shakes, however, could be related to the inhibition of GAD and a hypothesis involving a compartmentalized action of DPA on GABA-metabolism has been proposed.

gamma-Aminobutyric acid-ergic analgesia: implications for gamma-aminobutyric acid-ergic therapy for drug addictions

Recent in vivo and in vitro studies regarding the involvement of gamma-aminobutyric acid (GABA)-ergic systems in analgesia and in opiate dependence have been reviewed and analyzed. It seems evident that GABA-ergic systems play a role in mediating the effects of opiates and that some interplay might exist between endogenous opioid systems and GABA-ergic systems. Systemic administration of GABA-agonists, GABA uptake blockers and inhibitors of GABA-alpha-oxoglutarate transaminase (GABA-T) can produce potent analgesic actions in experimental animals and in man. Further study of such agents might lead to the development of new analgesics and/or new drugs for treating certain types of drug addiction.