Brain cyclic nucleotides and the development of convulsion, with reference to the anticonvulsant activity of diazepam

Neurochemical consequences of status epilepticus induced in rats by coadministration of lithium and pilocarpine

Status epilepticus was produced in rats by administering pilocarpine (30 mg/kg, s.c.) 16 h after treatment with LiCl (3 meq/kg, i.p.). After 35 min of status epilepticus, several parameters of cholinergic activity were measured. Seizures had no effect on the in vivo concentration of acetylcholine or choline in cerebellum, cortex, hippocampus, or striatum. Synaptosomal high-affinity choline transport was also not changed by seizures in hippocampus, cortex, or striatum. Cortical slices from seizing rats had elevated concentrations of acetylcholine and released acetylcholine at a greater rate than did controls, but these effects seemed to be due to a reduction in the postmortem hydrolysis of acetylcholine. Synaptosomal 45calcium uptake during 2 to 60 s of incubation was no different from control rates in tissue prepared from seizing rats. These results indicate that presynaptic cholinergic activity is not markedly altered by 35 min of continuous seizure activity induced by lithium and pilocarpine. In contrast, the in vivo concentration of cyclic guanosine 5'-monophosphate was elevated above control values in seizing rats by 57 to 170% in cerebellum, cortex, hippocampus, and striatum.

Cerebellar cyclic nucleotides and the development of convulsion, with reference to the anticonvulsant activity of diazepam

Dibutyryl cyclic GMP (DbcGMP) or dibutyryl cyclic AMP (DbcAMP) given to rats intracerebellarly in a dose of 200 nmol/head produced electroencephalographic convulsive changes. Intracerebellar (i.c.) administration of lower doses (100 nmol/head) of DbcGMP and DbcAMP and 200 nmol/head of norepinephrine (NE) and glutamate (Glu) facilitated the pentylenetetrazol (PTZ)-induced convulsions. Diazepam (100 nmol/head, i.c.) suppressed the PTZ-induced convulsions. GABA (400 nmol/head, i.c.) did not affect the PTZ-induced convulsions. These results suggest that DbcGMP, DbcAMP and Glu inhibit seizure control mechanisms in the cerebellum, and that one of the sites of the anticonvulsant action of diazepam is located in the cerebellum.