ELECTRICAL AND SYNAPTIC PROPERTIES OF EMBRYONIC LUTEINIZING-HORMONE-RELEASING HORMONE NEURONS IN EXPLANT CULTURES

Voltage- and ligand-activated channels in embryonic neurons containing luteinizing hormone-releasing hormone (LHRH) were studied by patch-pi pette, whole-cell current and voltage clamp techniques. LHRH neurons w ere maintained in explant cultures derived from olfactory pit regions of embryonic mice. Cells were marked intracellularly with Lucifer yell ow following recording. Sixty-two cells were unequivocally identified as LHRH neurons by Lucifer yellow and LHRH immunocytochemistry. The cu ltured LHRH neurons had resting potentials around -50 mV, exhibited sp ontaneous discharges generated by intrinsic and/or synaptic activities and contained a time-dependent inward rectifier (I-ir). Voltage clamp analysis of ionic currents in the LHRH neuron soma revealed a tetrodo toxin-sensitive Na+ current (I-Na) and two major types of K+ currents, a transient current (I-A), a delayed rectifier current (I-K) and low- and high-voltage activated Ca2+ currents. Spontaneous depolarizing sy naptic potentials and depolarizations induced by direct application of gamma-aminobutyrate were both inhibited by picrotoxin or bicuculline, demonstrating the presence of functional gamma-aminobutyrate type A s ynapses on these neurons. Responses to glutamate were found in LHRH ne urons in older cultures. Thus, embryonic LHRH neurons not yet position ed in their postnatal environment in the forebrain contained a highly differentiated repertoire of voltage- and ligand-gated channels.