Myorelaxant effect of baclofen injected to the nucleus accumbens septi

Involvement of the nucleus accumbens in the myorelaxant effect of baclofen in rats

The study was designed to search for brain structures responsible for the myorelaxant action of baclofen. Rats were chronically implanted with cannulae in the medial nucleus accumbens (NAS). The muscle tone was increased by reserpine (10 mg/kg i.p.) and measured as a resistance of the hind foot, developed in response to successive passive bendings and straightenings in the ankle joint. (+/-)Baclofen (1 or 2.5 mg/0.5 microliter), injected bilaterally into the NAS 1.5 h after pretreatment with reserpine, decreased the muscle tone of flexors and extensors enhanced by that compound. It is suggested that GABAB receptors of the NAS are involved in the myorelaxant action of baclofen.

The involvement of NMDA receptors in acute and chronic effects of ethanol

Recent evidence indicates involvement of excitatory amino acid receptors sensitive to N-methyl-d-aspartate (NMDA) in the action of ethanol (EtOH). Pronounced inhibition of NMDA receptor function is seen in vitro with concentrations of EtOH corresponding to those present during alcohol intoxication in humans. The present study was devoted to investigate the role of NMDA receptors in the action of EtOH in rats. Acute experiments showed antagonism by EtOH of convulsions induced by intracerebroventricular injection of NMDA. A similar effect was seen with a high dose of diazepam. Convulsions induced by an agonist of another excitatory amino acid receptor subtype, kainate, were also inhibited by EtOH. An uncompetitive antagonist of NMDA receptors, 5-methyl-10,11-dihydro-5H-dibenzocyclohepten-5,10-imine maleate (MK-801), potentiated EtOH-induced loss of righting, but attenuated the hypothermic action of EtOH. Moreover, MK-801 inhibited audiogenic convulsions in EtOH withdrawn rats. At the same time the effect of a proconvulsive dose of NMDA was not enhanced. Tolerance to the myorelaxant action of both EtOH and MK-801 upon repetitive administration was seen. Also some degree of cross-tolerance was observed. Moreover, MK-801 failed to modify EtOH preference in rats. The present results support involvement of NMDA receptors in expression of some acute and subchronic actions of EtOH and in expression of EtOH withdrawal.

Direct mechanomyographic measurement of the myorelaxant action of baclofen and diazepam in normal and reserpinized rats

A pathologically increased muscle tone is frequently observed. Objective methods for measuring directly the muscle-relaxant action of drugs in laboratory animals are scarce. This study shows that a computerized mechanomyographic method allows the assessment of myorelaxant drugs. The method consists of the successive bending and straightening of the rat's foot in the ankle joint and the separate measurement of resistance of extensors and flexors of the hind foot to passive movements. The two well-known antispastic drugs diazepam and baclofen reduced the normal muscle tone in both groups of muscles in non-treated animals as well as the muscle tone increased by reserpine (10 mg/kg i.p.). The results obtained show that the mechanomyographic method directly and reliably reveals the myorelaxant action of drugs.