Release of Luteinizing Hormone by Electrical Stimulation of the Medial Preoptic Area and Arcuate Nucleus in the Male Rat

1974 ◽  
Vol 15 (5) ◽  
pp. 249-254 ◽  
Author(s):  
J.F. Masken ◽  
C.L. Kragt ◽  
R.V. Gallo ◽  
W.F. Ganong
Keyword(s):  
Electrical Stimulation ◽  
Luteinizing Hormone ◽  
Arcuate Nucleus ◽  
Preoptic Area ◽  
Medial Preoptic Area ◽  
Male Rat ◽  
Stimulation Of

GONADOTROPHIN SECRETION AFTER ELECTRICAL STIMULATION OF THE PREOPTIC AREA DURING THE OESTROUS CYCLE OF THE RAT

1974 ◽  
Vol 62 (3) ◽  
pp. 589-604 ◽  
Author(s):  
G. FINK ◽  
M. S. AIYER
Keyword(s):  
Electrical Stimulation ◽  
Luteinizing Hormone ◽  
Pituitary Gland ◽  
Anterior Pituitary ◽  
Preoptic Area ◽  
Medial Preoptic Area ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Early Afternoon ◽  
Stimulation Of

SUMMARY The responsiveness of the hypothalamo-hypophysial axis to electrical stimulation of the medial preoptic area was tested at various times during the oestrous cycle of the rat. Animals were anaesthetized with sodium pentobarbitone, and glass-insulated bipolar platinum electrodes were stereotaxically implanted in the medial preoptic area. The stimulus consisted of accurately balanced biphasic rectangular pulses, height 500 μA, duration 2 ms and frequency 60 Hz, applied in trains of 30 s intervals. The concentration of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in blood samples withdrawn from the external jugular vein immediately before and at frequent intervals up to 1 h after application of the stimulus was determined by radioimmunoassay. In all animals the stimulus was applied for a period of 15 min, for it was found that under these conditions the profiles of LH and FSH produced in individual animals were similar to those which followed the i.v. injection of 50 ng synthetic luteinizing hormone releasing factor (LH-RF)/100 g body wt, the minimal ovulatory dose of LH-RF in our laboratory. Both for LH and FSH, the profiles of responsiveness of the hypothalamo-hypophysial axis to electrical stimulation through the oestrous cycle resembled closely the profile of responsiveness of the anterior pituitary gland to LH-RF administered intravenously. There was a relatively gradual increase in pituitary sensitivity, in terms of the mean maximal increments, between the early afternoon of dioestrus and pro-oestrus, followed by an abrupt and marked rise which reached a peak at 18.00 and 21.00 h of pro-oestrus for LH and FSH, respectively. Sensitivity of the hypothalamo-hypophysial axis declined through oestrus and metoestrus reaching a nadir at 13.30 h of dioestrus. While these results do not exclude a change in sensitivity of the neural component of the hypothalamo-hypophysial axis during the oestrus cycle, they do indicate that the timing and magnitude of changes in sensitivity of the anterior pituitary gland to both endogenous and exogenous LH-RF are similar. This raises the possibility that a marked increase in the secretion of LH-RF during the afternoon of pro-oestrus may not be necessary for the occurrence of the surge of LH and FSH, for conceivably the latter could depend on a change in sensitivity of pituitary gonadotrophs to constant or only slightly increased levels of LH-RF in hypophysial portal blood. Our findings are compared with those of workers who have employed electrochemical stimulation of the preoptic area.

LESIONS OF THE SUPRACHIASMATIC NUCLEI AND THE SEROTONIN-DEPENDENT PHASIC RELEASE OF LUTEINIZING HORMONE IN THE RAT: EFFECTS ON DRINKING RHYTHMICITY AND ON THE CONSEQUENCES OF PREOPTIC AREA STIMULATION

1980 ◽  
Vol 84 (2) ◽  
pp. 231-236 ◽  
Author(s):  
C. W. COEN ◽  
P. C. B. MacKINNON
Keyword(s):  
Electrical Stimulation ◽  
Luteinizing Hormone ◽  
Preoptic Area ◽  
Ovariectomized Rats ◽  
Suprachiasmatic Nuclei ◽  
Lh Release ◽  
Radiofrequency Lesions ◽  
Pharmacological Manipulations ◽  
Stimulation Of ◽  
Phasic Release

Ovariectomized rats in which <7% of the suprachiasmatic nuclei had been spared by bilateral radiofrequency lesions were distinguishable from those with >40% of the nuclei by their consistent failure to show the oestrogen-induced daily surge of LH, either with or without pharmacological manipulations of serotonin (5-HT), and also by their loss of the normal rhythmicity of drinking. Minor damage to structures adjacent to the suprachiasmatic nuclei was similar in both groups. The identical facility with which electrical stimulation of the preoptic area induced LH release in the two groups of animals suggested that they were not characterized by different degrees of damage to the preopticotuberal pathway. These results are considered in relation to evidence indicating that the suprachiasmatic nuclei represent the densest concentration of 5-HT terminals in the forebrain and also the site of a mechanism involved in the generation of circadian rhythms.

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