An ex vivo multi-electrode approach to evaluate endogenous hormones and receptor subtype pharmacology on evoked and spontaneous neuronal activity within the ventromedial hypothalamus; translation from female receptivity.
BACKGROUND
The ventromedial hypothalamus (VMH) controls female rodent copulatory behavior, which can be modulated by injection of various compounds into the VMH. Aim. The aim was to determine whether evoked excitatory postsynaptic potentials (EPSPs) or single-unit activity within the VMH ex vivo is a better parameter to predict lordosis.


METHODS
VMH slices were placed onto a 64 microelectrode chip and spontaneous single-unit activity was recorded or slices stimulated to evoke EPSPs.


METHODS
The sodium channel blocker, tetrodotoxin and alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX) inhibited EPSPs, confirming EPSPs were glutamatergic in origin. The GABA(A) antagonist bicuculline potentiated EPSPs implying endogenous GABA tone. Single-unit activity was abolished by tetrodotoxin but unaffected by DNQX or bicuculline.


RESULTS
Glutamatergic neurotransmission was greatest during metestrous and following ovariectomization. The number of regions within the VMH eliciting single-unit activity was reduced following ovariectomy without changing spike frequency. Adrenergic agents increasing lordosis via the VMH in vivo, decreased glutamate neurotransmission but increased single-unit activity. Conversely, agents decreasing lordosis via the VMH increased glutamatergic neurotransmission and inhibited single-unit activity (8-OH-DPAT, [D-Ala(2), N-Me-Phe(4), Gly-ol(5)]-enkephalin, corticotropin releasing factor, bicuculline). Melanocortin and pituitary adenylate cyclase-activating polypeptide agonists had no effect.


CONCLUSIONS
Here we present a novel, robust VMH in vitro technique that (i) is consistent with the hypothesis that glutamate via non-NMDA receptors inhibits lordosis; (ii) glutamate is under the endogenous tone of GABA and steroid hormones; (iii) inhibition of lordosis during metestrous and following ovariectomy potentiates glutamatergic neurotransmission; (iv) activation of G(q)- and G(i)-coupled receptors decreases and increases glutamate neurotransmission, respectively, with an inverse correlation on single-unit activity; (v) activation of G(s)-coupled receptors has no direct effect on glutamate or single-unit activity; and (vi) potency, receptor subtypes and localization can be determined prior to in vivo studies.
Booth
Clair
C
Pfizer, Discovery Biology, Sandwich, Kent, UK.
Wayman
Christopher P
CP
Jackson
Vivienne Margaret
VM
D000322:Adrenergic Agonists; D000818:Animals; D004566:Electrodes; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology*; D005260:Female; D018756:GABA Antagonists / Q000494:pharmacology; D018698:Glutamic Acid; D066298:In Vitro Techniques; D010052:Ovariectomy; D051381:Rats; D017207:Rats, Sprague-Dawley; D012726:Sexual Behavior, Animal / Q000502:physiology*; D013223:Statistics as Topic; D014697:Ventromedial Hypothalamic Nucleus / Q000502:physiology*
D000322:Adrenergic Agonists; D018756:GABA Antagonists; D018698:Glutamic Acid