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Voltage-and ligand-activated channels in embryonic neurons containing luteinizing hormone-releasing hormone (LHRH) were studied by patch-pipette, whole-cell current and voltage clamp techniques. LHRH In mammals, luteinizing hormone (LH) pulses are closely correlated with increased activities in as yet unidentified mediobasal hypothalamic neurons (1-3) which are believed to regulate the secretory activities of LH-releasing hormone (LHRH)-containing neurons. Due to the small number of LHRH neurons in brain, their small diameter, and their dispersed anatomical distribution, very few electrical recordings from identified LHRH neurons either in vivo or in vitro are available (4, 5). Consequently, the underlying electrophysiological and synaptic properties of LHRH neurons and information about their basic physiological properties have been largely deduced from extensive studies on the immortalized hypothalamic (LHRH-cell) neuronal cell line GT1 (6). Cells of the GT1-3 and -7 sublines possess a rich array of ion channels (7-11) and, under some circumstances, exhibit pulsatile LHRH secretion (9,(11)(12)(13)(14). However, the extent to which these electrical, receptor, and secretory properties of GT1 cells are found in actual LHRH neurons is unknown.Our aim was to study the electrophysiological and synaptic properties of primary LHRH neurons. Ontogenetic studies have shown that LHRH neurons originate from progenitor cells in the olfactory placode and thereafter migrate from the olfactory pit (OP) into the forebrain during prenatal development (15,16). LHRH neurons can be cultured from embryonic olfactory placodal regions (17, 18), and cells maintained in these explants secrete LHRH in a pulsatile mannerThe publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact. 3918(19). We report here successful intracellular recordings from 62 identified embryonic LHRH neurons and describe their highly differentiated voltage-and ligand-gated ion-channel properties.MATERIALS AND METHODS Preparations. OP regions ("0.5 mm3) were aseptically dissected from day-11.5 mouse embryos (17), plated on glass coverslips (24 mm x 12 mm, Gold Seal, no. 1 thickness), and placed in 35-mm Petri dishes (Falcon). Tissues were fed twice a week with serum-free Eagle's basal medium (20) and maintained in humidified air plus 5% CO2. Cultures typically received a single dose of 5-fluoro-2'-deoxyuridine (80 ,uM) on day 3 for 3 days. This treatment reduced the proliferation of dividing cells and vastly improved the visualization of LHRHlike (bipolar) neurons under phase-contrast microscopy (see Fig. 1). Tissues were maintained for 6-14 days in vitro, during which time LHRH cells migrated into the thin peripheral tissue areas (17), thereby facilitating electrophysiological recordings.Electrophysiological Recordings. The cultures on coverslips were transferred to a recording chamber on a Nikon M inverted mi...

During development, a subpopulation of olfactory neurons transiently expresses GABA. The spatiotemporal pattern of GABAergic expression coincides with migration of luteinizing hormone-releasing hormone (LHRH) neurons from the olfactory pit to the CNS. In this investigation, we evaluated the role of GABAergic input on LHRH neuronal migration using olfactory explants, previously shown to exhibit outgrowth of olfactory axons, migration of LHRH neurons in association with a subset of these axons, and the presence of the olfactory-derived GABAergic neuronal population. GABAA receptor antagonists bicuculline (10(-5) M) or picrotoxin (10(-4) M) had no effect on the length of peripherin-immunoreactive olfactory fibers or LHRH cell number. However, LHRH cell migration, as determined by the distance immunopositive cells migrated from olfactory pits, was significantly increased by these perturbations. Addition of tetrodotoxin (10(-6) M), to inhibit Na+-transduced electrical activity, also significantly enhanced LHRH migration. The most robust effect observed was dramatic inhibition of LHRH cell migration in explants cultured in the presence of the GABAA receptor agonist muscimol (10(-4) M). This study demonstrates that GABAergic activity in nasal regions can have profound effects on migration of LHRH neurons and suggests that GABA participates in appropriate timing of LHRH neuronal migration into the developing brain.