Antidromic activation of rat dorsomedial hypothalamic neurons from locus coeruleus and median eminence.

In rats anesthetized with urethane, single unit activity was recorded in the hypothalamic dorsomedial nucleus (DMH) to obtain antidromic response to stimulation of locus coeruleus (LC) and median eminence (ME). Ninety-two cells were activated antidromically from LC and/or ME. Antidromic latencies to LC stimulation ranged from 7 to 39 msec and those to ME stimulation ranged from 5 to 20 msec. Approximately 13% of the neurons recorded revealed antidromic responses simultaneously from LC and ME, and they were found to bifurcate near the soma. The majority of DMH neurons projecting to LC alone were not spontaneously active, while those projecting to ME tended to discharge spontaneously.