Intracellular Membrane and Synaptic Properties in Medial Preoptic Slices Containing the Sexually Dimorphic Nucleus of the Rat

Passive and active electrophysiological properties of neurons (n=46) in the medial preoptic area (MPOA) were studied in hypothalamic slices from rats (primarily males). This investigation evaluated whether the MPOA contains a heterogeneous population of cell types, defined on the basis of electrophysical properties such as low-threshold Ca2+ spikes (LTS) and current-voltage (I-V) relations. Evoked and spontaneous synaptic potentials were also studied in these neurons. Electrical properties were compared between neurons in the sexually dimorphic nucleus of the preoptic area (SDN-POA) with those situated in other parts of the MPOA. Biocytin-injected neurons (n-24) were found in the SDN-POA, as well as other parts of the medial preoptic nucleus and MPOA. Stained neurons had 1 or 2 primary dendrites (46% of stained cells) or had multipolar dendritic arrays (54% of cells); dendrites were aspiny or sparsely spiny and displayed limited branching. Morphologically definable cell types were not specific to medial preoptic subdivisions.