Responses of arcuate neurons to some putative neurotransmitters in perfused rat hypothalamic slices : Effects of in vivo and in vitro estrogen treatments.

Abstract

The responses of neurons in the arcuate nucleus (ARC) to yaminobutyric acid (GABA), glycine, serotonin (5-HT), norepinephrine (NE), and dopamine (DA) were examined in hypothalamic slices from ovariectomized rats either treated or untreated with estrogen. In estrogenuntreated preparations, spontaneous unit activity of the majority of neurons identified antidromically by the median eminence (ME) stimulation was depressed by GABA and glycine. When effective, 5-HT was predominantly excitatory and DA was predominantly inhibitory, while NE evoked both excitatory and inhibitory responses. The IS-SD block in evoked spikes was also occasionally observed following GABA and glycine perfusion. The responsiveness of unidentified neurons, which were not activated by the ME stimulation, to agents other than 5-HT did not differ from that of antidromically identified neurons. Responses of unidentified neurons to 5-HT were predominantly inhibitory. Subcutaneous injection of 20,ug of 17/3-estradiol-benzoate 2 days prior to the experiments did not significantly affect the responsiveness of both identified and unidentified neurons to GABA, 5-HT, DA, and NE. Contrarily, preincubation of slices in 17/3-estradiol-containing medium (10 nM) for 1 h significantly increased the responsiveness of unidentified, but not identified, neurons to the inhibitory action of NE. These results suggest that GABA, glycine, 5-HT, NE, and DA play some functional roles in controlling the excitability of tuberoinfundibular (TI) neurons in the ARC. It is also suggested that the negative feedback effect of estrogen is mediated, at least in part, by increased responsiveness of ARC neurons other than TI neurons to the inhibitory action of NE.

Roles of .GAMMA.-aminobutyric acid and serotonin in the arcuate nucleus in the control of prolactin and luteinizing hormone secretion.

“…We previously showed that 5-HT facilitated and inhibited spontaneous activity of 49 and 23%, respectively, of presumed TI neurons in the ARC (NIsHIHARA et al, 1986). It is possible that 5-HT directly inhibits the excitability of TI dopaminergic neurons which release dopamine as a PRL releaseinhibiting hormone.…”

Neurons in the Rat Arcuate Nucleus Are Hyperpolarized by GABA_B and μ-Opioid Receptor Agonists: Evidence for Convergence at a Ligand-Gated Potassium Conductance

“…In fact, implantation of GABA directly into the ARC has been reported to decrease the release of lu teinizing hormone [23]. Again, extracellular recordings have in dicated that GABA decreases the activity of most ARC neurons [24], GABA acts on at least two different receptors. Activation of the GABAa receptor increases a chloride conductance [for review see 25].…”

Postsynaptic Effects of Prolactin and Estrogen on Arcuate Neurons in Rat Hypothalamic Slices

“…Side-by-side bipolar electrodes, made of stainless steel wires (diameter: 100 pm) insulated except at the tip, were used for the stimulation. The sti mulating electrode was placed on the ME, and identification of neurons showing action potentials with antidromic features was made as reported previously (12], By the perfusion method, 3.7-10 nM l7|i-estradiol (E2 ; Sigma) or 3-5 pg/m l PRL (NIADDKrPRL-B-5, NIADDK-NIH) was applied to the slices. Changes in the firing rate greater than 30% or that in the preceding period were regarded as significant.…”

“…The animals were sacri ficed by decapitation and sagittal medial-hypothalamic slices (300-400 pm in thickness), bordered anteriorly by the optic chiasm and posteriorly by the mammillary body, were prepared as pre viously described (12). Slices were preincubated for more than 30 min in the regular medium (concentrations in mM: NaCI 124; KC1 5; KH2 PO4 1.25; MgS04 1.3; NaHCOj 26; CaCI: 1.2, and glucose 10) saturated with an O2/C O 2 (95%/5%) gas mixture at 36 °C, and were then transferred to the recording chamber.…”