A pharmacological investigation of the electrically evoked convulsive activity induced by administration of catechol in the anaesthetized rat

Sites and mechanisms of action of catechol (1,2-dihydroxybenzene) in the rat olfactory cortex slice

Synaptic transmission in the isolated olfactory cortex slice from the rat was monitored by recording the surface field potentials evoked on lateral olfactory tract (LOT) stimulation. Catechol (approximately 0.05 to 2 mM) caused a concentration-dependent, partially reversible increase in the amplitudes of all field potentials. In a series of conditioning experiments, catechol (1 mM) potentiated postsynaptic inhibition by a mechanism which was at least partially picrotoxin-insensitive. When the relationship between the stimulus input and evoked output was investigated in picrotoxin-treated slices, for a given tract action potential amplitude, catechol (0.25 and 0.5 mM) increased the amplitude of the field potential known as the N-wave; in contrast, for a given N-wave amplitude, the latency of the population spike was increased. Catechol (1 mM) increased the K+-evoked release of endogenous aspartate by a tetrodotoxin-insensitive mechanism whereas the release of glutamate and gamma-aminobutyric acid (GABA) was unaffected. Catechol (1 mM) had no effect on submaximal depolarizations evoked by L-aspartate, L-glutamate or GABA. It is concluded that catechol potentiates excitatory transmission at the LOT-superficial pyramidal cell synapse, possibly by increasing evoked transmitter release. Other synaptic actions of catechol may be consequent upon this increased excitatory input but the results do not exclude the possibility of separate and distinct actions on polysynaptic transmission.

Non involvement of gamma-aminobutyric acid in catechol-induced seizures

The effects of certain anticonvulsant agents, namely, valproate, diazepam and phenobarbitone were investigated on catechol-induced spontaneous and evoked convulsions, in anaesthetized rats and mice. Valproate and diazepam significantly reduced the intensity of spontaneous convulsions and the frequency of occurrence of the longer-latency components (M2 and M3) of the evoked muscle response. Phenobarbitone significantly reduced spontaneous convulsions and the M3 component of the evoked muscle response. None of the drugs affected the short latency M1 component indicating a supra-spinal site of action of these drugs. Agents which modify gamma-aminobutyric acid (GABA)-mediated transmission were without effect on the frequency of occurrence of M1, M2 or M3. The results suggest that the convulsant action of catechol is not dependent on antagonism of GABA-mediated inhibition.

Some characteristics of the long-latency component of the evoked muscle response induced by administration of catechol to the anaesthetized rat: a neurophysiological and neuropharmacological investigation

Administration of catechol to rats anaesthetized with urethane produces a central excitatory state during which an EMG consisting of three temporally distinct components (M1, M2 and M3) can be recorded from forelimb and hindlimb muscles to electrical stimulation of cutaneous afferents. The probability of occurrence of all three components was measured in flexor and extensor muscles of fore- and hindlimb and showed that the long latency component (M3) occurred less frequently in hindlimb muscles than forelimb and that its probability of occurrence in hindlimb extensors was significantly reduced as compared to flexors. A possible reflex pathway for this long latency component of the EMG is suggested. Phenobarbitone (5 mg kg-1 i.v.) had no significant effect on the probability of occurrence of M1, M2 or M3. These results suggest that the long latency component (M3) is not due to activation of a spino-bulbo-spinal reflex as has been previously suggested. Cholinoceptor blocking drugs were found to reduce significantly the probability of occurrence of M2 and M3 and anticholinesterases to increase the probability of M2. None of the drugs was found to affect the short latency M1 component of the EMG. These results are discussed in relation to the possible reflex pathways of all three components of the EMG.

The effect of the convulsant agent, catechol, on neurotransmitter uptake and release in rat brain slices

1 The effect of catechol on uptake and K+-stimulated release of gamma-aminobutyric acid (GABA), D-aspartate, noradrenaline and acetylcholine has been studied in slices of cerebral cortex and thalamus. 2 Low concentrations of catechol did not influence the uptake of any of the neurotransmitters in either brain area. 3 Noradrenaline release was unaffected by catechol. 4 Acetylcholine release from both cortical and thalamic slices was inhibited by high concentrations of catechol. This phenomenon is unlikely to be related to catechol-induced convulsions. 5 Catechol (100 microM) inhibited GABA release from cortical slices by 28%. However, at a concentration of 10 microM catechol enhanced the release of D-aspartate from thalamic slices by over 100%. 6 Potentiated release of excitatory amino acid transmitters may contribute to the enhanced excitability of thalamic cells which occurs during sensory myoclonus induced by low doses of catechol.

5-Hydroxytryptamine and myoclonus induced by 1,2-di-hydroxybenzene (catechol) in the guinea-pig

Myoclonus induced by catechol in the guinea-pig is not altered by manipulation of cerebral 5-hydroxytryptamine (5-HT). The administration of catechol does not alter brain levels of 5-HT or its metabolite 5-hydroxyindole acetic acid. This form of myoclonus therefore is not of relevance to the 5-HT-sensitive post-anoxic action myoclonus occurring in man.