Here we may have the link I postulated between Gamma-OH and Oxytocin !

Claude de Contrecoeur patanie at pasdepub.com
Fri Aug 14 08:04:18 EST 1998



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J Neurophysiol 1996 Aug;76(2):1166-1179 

GABAB receptors presynaptically modulate excitatory
synaptic transmission in the rat supraoptic nucleus in
vitro.

Kombian SB, Zidichouski JA, Pittman QJ

Neuroscience Research Group, University of Calgary, Alberta, Canada. 

1. The effect of gamma-aminobutyric acid-B (GABAB)-receptor activation
on excitatory synaptic
transmission in the rat supraoptic nucleus (SON) was examined using
the nystatin perforated-patch
whole cell recording technique in coronal hypothalamic slices. 2.
Stimulation of the hypothalamic
region dorso-medial to the SON elicited glutamate and
GABAA-receptor-mediated synaptic
responses in electrophysiologically identified magnocellular
neurosecretory cells. 3. Bath application
of the GABAB-receptor agonist, +/- -baclofen reversibly reduced
pharmacologically isolated,
glutamate-mediated excitatory postsynaptic currents (EPSCs) in a
concentration-dependent manner.
At the concentrations used, baclofen altered neither the postsynaptic
conductances of these cells nor
their response to bath applied
alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid
(AMPA). 4. The baclofen-induced synaptic depression was accompanied by
an increase in paired
pulse facilitation (PPF). This increase in PPF, as well as the
synaptic depression, was blocked by the
GABAB-receptor antagonists CGP36742 and saclofen. 5. In addition to
blocking the actions of
baclofen in this nucleus, CGP36742 caused an increase in the evoked
EPSC amplitude without
altering postsynaptic cell conductances or responses induced by
bath-applied AMPA. Contrary to
the action of CGP36742, saclofen caused a baclofen-like depression of
the evoked EPSC,
suggesting that it may act as a partial GABAB receptor agonist. 6.
These results indicate that the
activation of presynaptic GABAB receptors reduces fast excitatory
synaptic transmission in the
SON. They further suggest that presynaptic GABAB receptors may be
tonically activated in vitro.
Thus GABAB receptors may influence the level of activity and
excitation of SON neurons and hence
modulate the secretion of the regulatory neuropeptides vasopressin and
oxytocin. 



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