Differential effects of an anxiogenic beta-carboline on single unit activity in the locus coeruleus and substantia nigra of the rat brain

The firing rates of single units in the substantia nigra pars reticulata, substantia nigra pars compacta and the locus coeruleus were recorded during the intravenous administration of beta-carboline-3-carboxylic acid ethyl ester (beta CCE). beta-Carboline-3-carboxylic acid produced a dose-dependent excitation in all units tested in the substantia nigra pars reticulata and a small inhibitory effect on some units in the substantia nigra pars compacta. It had no effect on the firing rates of single units in the locus coeruleus, but did prove effective in reversing inhibition induced by diazepam in this nucleus. The relevance of the findings to the anxiogenic effects of beta-carboline-carboxylic acid ethyl ester are discussed.