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Properties of ventromedial hypothalamic neurons with axons to midbrain central gray

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Summary

In female rats anesthetized with urethane, 151 neurons in and around the ventromedial nucleus of the hypothalamus were identified by antidromic activation as having axonal projection to the mesencephalic central gray at the midcollicular level. Identified neurons were most numerous in the rostral part and at the borders of the nucleus.

Antidromic spike latencies, constant for a given cell to stimulation with fixed intensity at a low repetition rate, had a wide range across cells (1.4–41.5 ms). In 37 cells, gradual increases in stimulus intensity allowed sudden discrete latency decreases as large as 9.8 ms. These may reflect activation of separate axonal branches of terminal arborizations.

Eleven among 43 tested cells were antidromically driven from the dorsal longitudinal fasciculus (DLF) at the diencephalic-mesencephalic junction as well as from the central gray. Latencies of DLF responses were always shorter than those from central gray. From this and collision experiments between central gray-evoked and DLF-evoked antidromic spikes, it was concluded that at least one quarter of mesencephalic projections from the ventromedial nucleus descend through DLF. The mean conduction velocity of these axons was 0.8 m/s, indicating that they belong to thin unmyelinated C-group fibers.

Thirty percent of the cell population studied received excitatory input from the cortical or medial nucleus of the amygdala. Four cells were identified as having projections both to the central gray and the amygdala.

Estrogen treatment of ovariectomized female rats caused no major changes in antidromic latency, absolute refractory period or resting activity of these identified hypothalamic neurons. However, the stimulation threshold for antidromic activation was significantly lower in the estrogen-treated animals.

Axons to the central gray from ventromedial hypothalamic neurons provide for hypothalamic bias on brain stem reflex paths, for reproductive and other behaviors.

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  1. Y. Sakuma

    Present address: Dept. of Physiology, Niigata University School of Medicine, 951, Niigata, Japan

Authors and Affiliations

  1. The Rockefeller University, 1230 York Avenue, 10021, New York, NY, USA

    Y. Sakuma & D. W. Pfaff

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  1. Y. Sakuma
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  2. D. W. Pfaff
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Additional information

Supported by NIH grant HD-05751 and by institutional grant from the Rockefeller Foundation for the study of reproductive biology

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Sakuma, Y., Pfaff, D.W. Properties of ventromedial hypothalamic neurons with axons to midbrain central gray. Exp Brain Res 46, 292–300 (1982). https://doi.org/10.1007/BF00237187

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  • DOI: https://doi.org/10.1007/BF00237187

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