AJP - Endocrinology and Metabolism, Vol 242, Issue 3 164-E170, Copyright © 1982 by American Physiological Society
Electrophysiologic correlates of steroid modulation of luteinizing hormone release
P. C. Leung, D. I. Whitmoyer and C. H. Sawyer
In both ovariectomized (OVX) and steroid-primed OVX freely moving rats,
attempts were made to correlate the effects of intraventricular
norepinephrine (NE) on multiunit activity (MUA) of different brain regions
with NE-induced alterations in blood LH levels. MUA-recording electrodes
were implanted in the diagonal band of Broca (DBB), medial preoptic area
(MPOA), arcuate nucleus (ARC) and/or ventromedial hypothalamic nucleus
(VMH). Steroid priming included 50 micrograms estradiol benzoate (EB) and
25 mg progesterone (P) 3 days prior to experiment. The unanesthetized
animals were bled via indwelling atrial cannulas before and after
intraventricular infusion of NE (10 micrograms in 2 microliters over 2
min). In OVX-primed rats NE lengthened the interval between episodic LH
peaks and decreased mean blood LH levels. In contrast, in OVX-EBP-primed
rats, NE stimulated an LH surge. Concurrent recording of MUA revealed that,
in OVX-unprimed rats, NE dramatically depressed MUA in both DBB-MPO and
ARC-VMH neurons. However, in OVX-EBP-primed rats, while still markedly
inhibiting ARC-VMH units, NE failed to depress MUA recorded in DBB-MPO
sites (some units were actually excited by NE), perhaps reflecting the
higher ratio of LHRH neurons/inhibitory neurons in DBB-MPO.
