Extranuclear dendrites of locus coeruleus neuronS: ACTIVATION BY glutamate
and modulation OF ACTIVITY by alpha adrenoceptors.
Ivanov, A., and G. Aston-Jones.
Division of Behavioral Neurobiology, Department of Psychiatry, Hahnemann
University, Mail Stop 403, Broad and Vine, Philadelphia, PA 19102.
APStracts 2:0221N, 1995.
SUMMARY AND CONCLUSIONS
1. Locus coeruleus (LC) neurons were recorded extra- and intracellularly in
rat brain slices. Effects of glutamate applied to the area of distal
extranuclear LC dendrites, and of alpha-2 adrenoceptors applied in the bath,
were determined on activity of these cells. 2. Glutamate applied to the area
of distal dendrites potently activated LC neurons. These responses were not
blocked by either 1 [mu]M TTX or 2 mM Co++/10 mM Mg++. This indicates that
glutamate acting directly on distal dendrites can potently activate LC
neurons. 3. Bath application of the alpha-2 adrenoceptor antagonists
yohimbine(1 [mu]M) or idazoxan (1 [mu]M) significantly increased responses of
LC neurons evoked by dendritic glutamate application. These antagonist
treatments also transiently decreased, and then increased, spontaneous
discharge activity in LC neurons. 4. Alterations in spontaneous and glutamate-
evoked activities after blockade of alpha-2 adrenoreceptors were not observed
in LC neurons of reserpinized rats. This indicates that the altered LC
activity and responsiveness to glutamate following alpha-2 antagonist
treatment in non-reserpinized slices are mediated via blockade of effects of
endogenously released noradrenaline. 5. The alpha-1 antagonist prazosin (1
[mu]M) caused a small but reliable decrease in the spontaneous firing rate of
LC neurons. After prazosin pre-treatment, alpha-2 antagonists did not evoke
the expected delayed increase in LC spontaneous firing and response to
glutamate application. These results indicate that activation of alpha-1
adrenoceptors may contribute to the delayed increase in excitability of LC
neurons after alpha-2 antagonist administration. The possible roles of alpha-1
and alpha-2 adrenoreceptors in regulation of spontaneous discharge rate and
glutamate-evoked responses in LC neurons are discussed.
Received 12 May 1995; accepted in final form 25 July 1995.
APS Manuscript Number J326-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 August 1995.