Effects of Limbic stimulation and the microinontophoresis of aminergic drugs on the single unit activity of hypothalamic neurosecretory cells (author's transl).

Abstract

Attempts were made to investigate the chemical nature of hypothalamic afferents from the extrahypothalamic structures which participate in the control of hypothalamic neurosecretory cells. Experimental procedures were discribed in the preceding report, except that of the electrical stimulation and the microinontophoresis. Some part of data obtained in this study were referred in the preceding report for improvement of statistic reliability. For electrical stimulation, side-by-side bipolar electrodes were placed in the medial preoptic area (MPO), medial amygdala (mAMYG) and dorsal hippocampus (dHPC) from the parietal surface of the brain and fastened to the cranium by dental resin. Microintophoresis of norepinephrine (NE), dopamine (DA) and acetylcholine (Ach) was carried out by using five-barrelled glass pipette on the antidromically activated units in the medical basal hypothalamus by the median eminence stimulation. Extracellular potentials were recorded by the central barrel of each electrode. One of the outer barrels was filled with physiological saline and used for control purpose. (1) Eelctrical stimulation of the MPO with train pulses of 0.2 msec duration and 300 muA intensity in 100 HZ for 5 sec, induced facilitation and inhibition in 26.4% and 9.4% of 106 tests, respectively. By the mAMYG stimulation with 500 muA, facilitation was seen in 18.8% and inhibition in 10.4%, of 96 tests. The HPC stimulation induced facilitation in 10.0% and inhibition in 23.3% of 90 tests. (2) Facilitatory effect of the MPO was most frequently seen in the ovariectomized and estrogen primed rats (58.8% of the tests). In contrast, the inhibitory effect of the dHPC was striking in the diestrus-I (40.0%). (3) Microiontophoresis of NE induced facilitation in 60.0% and inhibition in 10.6% of 66 identified cells. DA induced facilitation in 45%, and inhibition in 11.7% of 60 tests. Ach induced facilitation in 41.4%, and inhibition in 13.8% of 58 tests. (4) By NE infusion, facilitation was most commonly seen in the proestrus (70.6%). Inhibition was most readily elicited by Ach infusion on the diestrus-I (30%). Facilitative effect of DA was eminent in the diestrus-I (81.8%). (5) Successive administration of NE and DA on identical units revealed that in 56.0%, the units were responsive to only one agent and the other was effectless. 25.5% of the units responded to both of NE and DA. (6) The conceidence of effects, either facilitation or inhibition, between that of electrical stimulation of the microinontophoresis, was calculated on 46 units. The facilitatory effect of the MPO was most commonly mimicked by NE infusion (81.8%), and the inhibitory effect of the dHPC by Ach infusion (46.7%). NE also mimicked facilitatory effect of mAMYG stimulation (73.3%). (7) Intraventricular infusion of 20 mug of NE induced significant increase of serum LH (p less than 0.05 to saline) when measured by radioimmunoassay, whereas DA resulted in a decrease of LH (p less than 0.01).