Ventromedial nucleus of the hypothalamus: Convergent excitatory and inhibitory responses to fimbria and stria terminalis stimulation

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Abstract
Field and extracellular unitary potentials were recorded in the ventromedial nucleus of the hypothalamus (VMH) of urethane‐anesthetized rabbits after stimulation of the fimbria and stria terminalis.Stimulation of the lateral portion of the fimbria, which carries fibers from the ventral subiculum of the hippocampal formation, evoked a two‐component response. An early excitatory response, with an average latency of 10 msec, predominated along the lateral margins of the VMH. A later inhibitory potential with an average latency of 15 msec was seen predominantly within the central portions of the VMH. Stimulation of the dorsal component of the stria terminalis produced two similar response patterns: an early excitatory response with an average latency of 16 msec, followed by an inhibitory potential with an average latency of 25 msec. The topographical distribution of these two components of the response was nearly identical to that produced by lateral fimbria stimulation. In contrast, stimulation of the ventral component of the stria terminalis evoked a simple excitatory response with an average latency of 10 msec which was maximal within the core of the VMH.Extracellular unitary recodings showed that the early negativity associated with stimulation of each of these three pathways reflects a monosynaptic excitation of VMH cells and that there was convergence of the three excitatory inputs at the single cell level.