AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 4 1291-R1298, Copyright © 1997 by American Physiological Society
Serotonergic modulation of hippocampal pyramidal cells in euthermic, cold-acclimated, and hibernating hamsters
D. J. Horrigan, B. A. Horwitz and J. M. Horowitz
Section of Neurobiology, Physiology, and Behavior, University of California, Davis 95616, USA.
Serotonergic fibers project to the hippocampus, a brain area previously
shown to have distinctive changes in electroencephalograph (EEG) activity
during entrance into and arousal from hibernation. The EEG activity is
generated by pyramidal cells in both hibernating and nonhibernating
species. Using the brain slice preparation, we characterized serotonergic
responses of these CA1 pyramidal cells in euthermic, cold-acclimated, and
hibernating Syrian hamsters. Stimulation of Shaffer-collateral/commissural
fibers evoked fast synaptic excitation of CA1 pyramidal cells, a response
monitored by recording population spikes (the synchronous generation of
action potentials). Neuromodulation by serotonin (5-HT) decreased
population spike amplitude by 54% in cold-acclimated animals, 80% in
hibernating hamsters, and 63% in euthermic animals. The depression was
significantly greater in slices from hibernators than from cold-acclimated
animals. In slices from euthermic animals, changes in extracellular K+
concentration between 2.5 and 5.0 mM did not significantly alter
serotonergic responses. The 5-HT1A agonist
8-hydroxy-2(di-n-propylamino)tetralin mimicked serotonergic inhibition in
euthermic hamsters. Results show that 5-HT is a robust neuromodulator not
only in euthermic animals but also in cold-acclimated and hibernating
hamsters.
