State-dependent effects of some neuropeptides and neurotransmitters on neuronal activity of the medial septal area in brain slices of the ground squirrel, Citellus undulatus
Ki. Zenchenko et al., State-dependent effects of some neuropeptides and neurotransmitters on neuronal activity of the medial septal area in brain slices of the ground squirrel, Citellus undulatus, NEUROSCIENC, 96(4), 2000, pp. 791-805
Neuronal activity of the medial septal area was recorded extracellularly in
brain slices taken from hibernating (winter) and waking (summer) ground sq
uirrels. The effects of neuropeptides identified in the brain tissue of hib
ernators (Thr-Ser-Lys-Tyr, Thr-Ser-Lys-Tyr-Arg and Asp-Tyr) on the backgrou
nd activity and responses to electrical stimulation of the median forebrain
bundle were analysed. For comparison, the effects of bath application of n
oradrenaline and serotonin were also tested. Spontaneous activity in half o
f all neurons (47-56%) was changed under the influence of neuropeptides in
hibernating ground squirrels, while in waking ground squirrels the proporti
on of responsive neurons was significantly lower (25-30%). The tendency for
higher efficacy in hibernating ground squirrels was observed for serotonin
; only noradrenaline was equally effective in both groups of animals. Elect
rically evoked responses of the medial septal nucleus-nucleus of the diagon
al band neurons were also strongly modulated by neuropeptides; their change
s could occur in the absence of shifts in the level and pattern of spontane
ous activity. All three neuropeptides had differential action on the level
of spontaneous activity, as well as on inhibitory and excitatory components
of electrically evoked responses. Thus, the character and distribution of
the effects were state dependent and differed greatly in hibernating and wa
king ground squirrels. The experiments confirmed that medial septal nucleus
-nucleus of the diagonal band neurons have higher excitability and responsi
veness to some neuropeptides and neurotransmitters in hibernating ground sq
uirrels.
The data obtained suggest an increased latent excitability and responsivene
ss of septal neurons during hibernation and their possible active participa
tion in urgent arousal under the influence of sensory signals. (C) 2000 IBR
O. Published by Elsevier Science Ltd.