Journal of Neuroscience, Vol 16, 123-129, Copyright © 1996 by Society for Neuroscience
Synaptically released histamine increases dye coupling among vasopressinergic neurons of the supraoptic nucleus: mediation by H1 receptors and cyclic nucleotides
GI Hatton and QZ Yang
Department of Neuroscience, University of California, Riverside 92521, USA.
Activating direct olfactory (glutamatergic) inputs to supraoptic nucleus
(SON) neurons increases interneuronal coupling in slices from lactating but
from not virgin or male rats. Studied here were influences on coupling of
another monosynaptic input to SON, the histaminergic tuberomammillary
nucleus (TM) projection, activation of which selectively excites phasically
firing (putative vasopressin) cells. Effects of TM stimulation and its
possible downstream consequences on Lucifer yellow (LY) dye coupling among
putative vasopressin cells were determined in male rat SONs. In
unstimulated slices, 12 LY injections (1 cell/SON) yielded eight single and
four pairs of coupled neurons. In slices in which TM was stimulated for 10
min at 10 Hz, 13 injections yielded 4 single and 28 coupled cells, with
groups of 2 to 4 cells coupled to the injected neuron, a threefold increase
in the number of coupled cells per injection (p < 0.02). Bathing slices
in medium containing 10 microM pyrilamine (H1 antagonist) blocked this
stimulation-induced coupling increase, suggesting mediation by activation
of guanylate cyclase-cGMP to which H1 receptors often are linked . Bathing
slices in medium containing 0.5- 1 mM 8-bromo-cGMP yielded results similar
to those of TM stimulation, a 2.5-fold increase over control in the number
of coupled cells per injection. Effects of TM stimulation on coupling also
were blocked by bathing slices in a guanylate cyclase inhibitor (10 microM
LY83583). In contrast to cGMP, 1 mM 8-bromo-cAMP significantly reduced
coupling. We conclude that synaptically released histamine increases
coupling via cGMP-dependent mechanisms.