Interaction of beta-adrenoceptor agonists with the serotonergic system in rat brain. A behavioral study using the L-5-HTP syndrome.

The effect of beta-adrenoceptor agonists on the behavioral effect of L-5-HTP in rats and mice was studied. All beta-agonists potentiated the behavioral syndrome elicited by L-5-HTP. However no indication for a correlation between their potencies to stimulate peripheral beta-receptors and their potencies to enchance L-5-HTP effect was found. The potentiating effect of salbutamol in rats was intensified by the MAO A inhibitor clorgyline, completely inhibited by (+/-)-propranolol and partly inhibited by WB-4101, while practolol was without effect. Lesions of 5-HT pathways by i.c.v. injections of 5,7-DHT impaired the potentiating effect of salbutamol in rats. In contrast, 6-OHDA lesions or alpha-methyl-p-tyrosine pretreatment were without effect. A central site of action of salbutamol is suggested by the fact that it intensified L-5-HTP effects also after i.c.v. administration. Therefore the results suggest that salbutamol facilitates 5-HT transmission in rat brain probably via stimulation of central beta receptors.