Acetylcholine Excites GABAergic Neurons of the Ferret Perigeniculate Nucleus Through Nicotinic Receptors. Lee, K. H., and D. A. McCormick. Section of Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510.
APStracts 2:0051N, 1995.
SUMMARY AND CONCLUSIONS
1. The actions of acetylcholine (ACh) on the GABAergic neurons of the perigeniculate nucleus (PGN) were investigated with the use of extra- and intracellular recording techniques in spontaneously spindling ferret thalamic slices maintained in vitro. 2. Local application of ACh to PGN neurons resulted in rapid depolarization followed by a longer lasting hyperpolarization. Neither of these responses were abolished by blockade of synaptic transmission with tetrodotoxin (TTX) nor with low Ca 2+ and elevated Mg 2+ solution, indicating that they are direct postsynaptic actions of ACh on PGN cells. Functionally, the rapid depolarizing response could activate both single spike activity, as well as low-threshold Ca 2+ spike-mediated bursts. 3. The fast depolarizing response to ACh was selectively blocked by application of the nicotinic antagonist hexamethonium, whereas the slow hyperpolarizing response to ACh was selectively blocked by application of the muscarinic antagonist (_)scopolamine. Application of both hexamethonium and (_)scopolamine blocked the modulation of PGN action-potential firing by ACh. 4. Local application of the nicotinic agonist 1,1-dimethyl-4- phenylpiperazinium (DMPP) resulted in a depolarizing response and an increase in membrane conductance, whereas application of the muscarinic agonist DL- muscarine chloride resulted in a hyperpolarizing response and an increase in membrane conductance. When applied to spontaneously spindling PGN cells, both DMPP and DL-muscarine blocked the occurrence of spindle oscillations. However, only DMPP was associated with depolarization and the generation of single spike activity. 5. These results indicate that the GABAergic cells of the PGN possess postsynaptic nicotinic as well as muscarinic receptors. Activation of the nicotinic receptors results in rapid depolarization of these neurons and can activate both single spike and burst activity. These responses may be important in the generation of pontogeniculooccipital (PGO) waves and membrane depolarizations during rapid-eye-movement (REM) sleep and arousal. 

Received 9 December 1994; accepted in final form 27 January 1995.
APS Manuscript Number J770-4.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  3 April 1995.