Neurophysiological and neurochemical studies on the action of the anticonvulsant gamma-hydroxy, gamma-ethyl, gamma-phenyl-butyramide

Efficacy of a putative GABA analog on synaptic transmission in the cat spinal cord

4-Hydroxy-4-phenylcaproamide (HPhCA), at high doses or rates of IV injection depressed the ventral root reflexes elicited by nerve or dorsal root stimulation. The D (direct) and I (synaptic) ventral root waves and the antidromic (A) dorsal root wave evoked by intraspinal stimulation were also depressed. Similar effects were produced when HPhCA was applied topically on the cord dorsum. At 80 mg/kg and 8 mg/kg/min, the spinal reflexes and the I wave were facilitated for 4 to 6 h, but the D and A waves were depressed. Intracellular recordings from motoneurons showed that HPhCA injection produced: hyperpolarization that lasted several hours, short lasting (< 20 min) facilitation of both EPSPs and IPSPs as well as spike-like potentials (SLPs) that were triggered by EPSPs even though the neuron was hyperpolarized. SLPs may reach the threshold for full spikes. Our results suggest that the spinal depression results from hyperpolarization of motoneurons and the initial facilitation appears to be presynaptic. The late facilitation may be produced by SLPs. HPhCA does not appear to mimic the actions of GABA in primary afferents fibers and motoneurons.

Effects of 3-hydroxy,3-ethyl,3-phenylpropionamide (HEPP) on rat models of generalized and focal epilepsy

The GABA withdrawal syndrome (GWS) is a new model of focal epilepsy in which paroxysmal activity is induced through the interruption of a chronic, intracortical infusion of GABA. Preliminary studies have shown extraordinary resistance of this epileptogenic activity to classic anticonvulsants including diazepam, the most effective agent for treating status epilepticus. However, GWS can be inhibited by GABA itself. The rat with petit mal-like seizures is a genetic model of generalized non-convulsive epilepsy (GNCE), with behavioral characteristics and electrical (spike-and-wave discharges) signs resembling absences. Moreover, GABAmimetics aggravate this type of seizure. Rats with GWS induced by cessation of a localized GABA infusion (50 micrograms/microliters/h for 24 h), and the rat model of GNCE, were treated with HEPP, a new anticonvulsant agent. In the case of GWS, the drug produced a significant decrease of focal spike activity in animals which started discharging at low frequencies while in rats with higher frequency discharge, HEPP was without effect. HEPP administered on the second day of the GWS in naive rats had no effect. In rats with GNCE, doses of 50 and 100 mg/kg i.p. blocked the spike-and-wave discharges. The higher dose produced sedation in this absence seizures model. Although the mechanism of action of HEPP is still unknown, its unique antiepileptic profile deserves further studies.

Effects of denzimol on benzodiazepine receptors in the CNS: relationship between the enhancement of diazepam activity and benzodiazepine binding sites induced by denzimol in the rat

Denzimol, a new anticonvulsant drug with a pharmacological profile similar to that of phenytoin, enhances the ataxic and antimetrazol activity of diazepam in rats without affecting its activity against picrotoxin-induced seizures. In vivo and ex vivo denzimol enhances the binding of 3H-flunitrazepam in cortex and in hippocampus but not in cerebellum. The possibility of this increase in the number of benzodiazepine binding sites contributing in some way to enhancement of the depressive and anticonvulsant activity of diazepam is discussed.