Distribution and properties of receptors for gonadotropin-releasing hormone (GnRH) were analyzed in the brain of adult male rats. Binding of the iodinated GnRH agonist Des-Gly¹⁰-(D-Ala⁶)-GnRH ethylamide was studied in hippocampus and anterior pituitary using three convergent approaches: quantitative autoradiography on frozen tissue, binding to fresh slices, and binding to crude membrane preparations. In all cases, binding was specific, saturable, and time, pH, and temperature dependent. Quantitative autoradiography revealed that the density of binding sites was high in the stratum oriens and stratum radiatum of the CA1-CA4 regions of Ammon’s horn. The pyramidal cell layer was faintly labelled. Binding was almost undetectable in the dentate gyrus. The highest density of sites (B_max = 11.6 + 1.0 fmol/mg protein) was observed in the stratum radiatum of the CA3 region. Under the same conditions the value obtained for pituitary tissues was 20.7 + 2.8 fmol/mg protein. Analysis of saturation curves indicated only one class of high-affinity sites for the hippocampus (CA₃; K_d = 0.28 + 0.03 nM) and for the pituitary (K_d = 0.29 ± 0.08 nM). Both native GnRH and GnRH antagonist were potent competitors of binding. Fresh slices and membrane preparations from whole hippocampus confirmed these autoradiographic data and yielded affinity constants of 0.28 + 0.01 and 0.52 + 0.08 nM, respectively. In addition, a very high binding density was present in the amygdaloid complex, while binding was barely detectable in the hypothalamus. These results demonstrate that high densities of specific GnRH receptors are present in areas concerned with the regulation of behavioral functions. GnRH may thus be involved as a neurotransmitter in the integration of endocrine and behavioral reproductive processes.

The purpose of this study was to determine whether gonadotropin-releasing hormone (GnRH) may exert a direct action on human prolactinomas. On a series of 17 adenomas, we studied the effect of GnRH on the in vitro prolactin (PRL) secretion of dispersed and perifused cells of 10 cases and the [125I]GnRH agonist binding on frozen sections of three out of the adenomas studied in perifusion and on the membrane preparations of seven other cases. Two 20-min pulses of GnRH (10(-7) mol/l) stimulated the in vitro PRL secretion of three adenomas out of 10 (increase of 200, 444 and 205%, respectively, above basal levels). The GnRH receptors of three adenomas bound GnRH agonist (Des-Gly10-(D-Ala6)-GnRH ethylamide). The binding was specific, with a high affinity (Kd = 0.60, 0.48 and 0.40 nmol/l) similar to that of two human anterior pituitaries obtained post-mortem (Kd = 0.70 and 0.40 nmol/l). Indirect immunoperoxidase revealed that the majority of the cells (60-90%) in all the adenomas studied contained immunoreactive PRL. Four of them also contained cells immunoreactive to the alpha-subunit of the glycoprotein hormones. In none of the prolactinomas were cells immunoreactive to antiserum of anti-beta-luteinizing hormone, anti-beta-follicle-stimulating hormone or anti-beta-thyrotropin. All the prolactinomas that were responsive to GnRH in perifusion experiments and/or bound specifically to [125I]GnRH agonist were also immunoreactive for alpha-subunit. These results show that GnRH, via GnRH specific receptors, exerts a stimulation on in vitro PRL secretion in a subset of prolactinomas characterized by the presence of alpha-subunit.

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F. BORSON-CHAZOT, N. NAJIMI, G. FILLTON, AND TRH binding sites have been visualized by autoradiography in the brain of several species's2 including the human,3 in particular in the hippocampus. Because 70% of brain TRH content is located outside the hypothalamus, and might modulate brain f~n c t i o n s ,~ it is of special interest, therefore, to characterize TRH brain receptors. This study was achieved in the hippocampus area (dentate gyrus) of newborn (control and sudden infant death syndrome: SIDS) and adult human (control and depression: suicide). MATERIAL AND METHODSBrain was removed 4-24 hours after demise and stored at -80°C. The hippocampus area was dissected and 20 micron sections were cut on a cryostat at -20°C and mounted on gelatin-coated slides. The tawed slides were preincubated 20 min at room temperature, then incubated with 10 nM [3H]MeTRH for 2 h at 4°C. The sections were washed four times with buffer (30 s each) and once (15 s) in distilled water.For biochemical studies, tissue sections were wiped off the slides with filters and counted. For autoradiography, the washed sections were dried, and we proceeded as previously reported2 for quantitative analysis by optical density measurements.

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