LATERAL HABENULAR INFLUENCE ON DORSAL RAPHE NEURONS

Previously, we have demonstrated that lateral habenula (LH) modulates the bioelectric activity of the hippocampus through the dorsal raphe n ucleus functional involvement. In this study we have, preliminarily, e lectrophysiologically identified two types of raphe neurons: ''slow'' (S cells, serotonergic in nature); and ''fast'' (F cells, presumably G ABAergic in nature). Then, we have shown that LH electrical stimulatio n at lower frequency induced an excitation of S and F neurons. LH stim ulation at higher frequency inhibited only S neurons. Furthermore, ion tophoretic NMDA excited S and F neurons. The excitatory effects of LH stimulation were antagonized by the iontophoretic 2-APV (NMDA antagoni st). Iontophoretic GABA inhibited only S neurons. Iontophoretic bicucu lline antagonized the LH-induced inhibition of S neurons. The data sug gested a direct (NMDA-mediated) and indirect (through the F GABAergic inhibitory interneuron) influence of the LH on the serotonergic effere nt neuron.