Alpha 1-adrenergic agonists act on the ventromedial hypothalamus to cause neuronal excitation and lordosis facilitation: electrophysiological and behavioral evidence.
To see if activation of central alpha 1-adrenergic receptors can cause facilitation of lordosis in rats, the behavioral effects of centrally administered alpha 1-agonists, methoxamine (MA) and phenylephrine (PhE), and related agents were studied. In ovariectomized rats treated with estrogen, infusion of MA, PhE, or a beta-agonist isoproterenol, into the lateral ventricle, or bilateral infusions of MA or PhE into the ventromedial hypothalamus (VMH) facilitated lordosis. Conversely, intra-VMH infusion of the alpha 1-antagonist prazosin (PZ) inhibited lordosis. Intra-VMH infusion of isoproterenol or an alpha 2-agonist clonidine, had no effect. Neither was the intra-VMH infusion of MA effective if: (i) the rats were not primed with estrogen; (ii) the tips of the cannulae were outside the VMH; or (iii) it was preceded by an intra-VMH infusion of the alpha 1b-antagonist, chloroethylclonidine (CEC). These results not only verify implications from recent studies that alpha 1-receptors in the hypothalamus are important for lordosis facilitation, but further show that the adrenergic facilitatory effect are: (i) mediated specifically by alpha 1b-subtype of the alpha 1-receptor, (ii) estrogen-dependent, and (iii) site-specific to VMH. To investigate neural mechanisms potentially underlying the lordosis-facilitating effect of alpha 1-activation, the actions of MA and PhE on the electrical activity of single neurons of the ventromedial nucleus of the hypothalamus (VMN) in vitro were studied.(ABSTRACT TRUNCATED AT 250 WORDS)
Rockefeller University, Laboratory of Neurobiology and Behavior, New York, NY 10021-6399.
L M
LM
Kow
G D
GD
Weesner
D W
DW
Pfaff
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000818:Animals; D004558:Electric Stimulation; D004594:Electrophysiology; D004967:Estrogens / Q000494:pharmacology; D005260:Female; D007276:Injections, Intraventricular; D009474:Neurons / Q000187:drug effects*; D010052:Ovariectomy; D011187:Posture / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012726:Sexual Behavior, Animal / Q000187:drug effects*; D013566:Sympathomimetics / Q000494:pharmacology; D014697:Ventromedial Hypothalamic Nucleus / Q000033:anatomy & histology / Q000187:drug effects*
D000316:Adrenergic alpha-Agonists; D004967:Estrogens; D013566:Sympathomimetics