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ROLE OF THE MESOLIMBIC CHOLINERGIC PATHWAYS IN THE INITIATION OF VOCALIZATION IN CATS AND RATS
Stefan M. Brudzynski
Department of Psychology, Brock University
St. Catharines, Ontario, L2S 3A1 Canada
The vocal component of defensive behaviour, with other accompanying manifestations, may be reproduced by an electrical or chemical stimulation of the brain. Results of studies during the last 10 years have demonstrated that the defensive or alarm vocalizations may be induced by cholinergic, muscarinic stimulation of the homolog areas of cat and rat brains. These cholinoceptive muscarinic regions occupy in both these species an elongated medial strip of tissue from the brainstem periaqueductal grey, medial tegmental regions, medial hypothalamic-preoptic and periventricular regions, up to the mediobasal forebrain and septal structures. The following presentation summarizes results of several recent studies which demonstrate that the ascending mesolimbic cholinergic projection from the laterodorsal tegmental nucleus is responsible for triggering the ultrasonic alarm calls (22 kHz calls) in adult rats. It is suggested that this mesolimbic cholinergic projection plays a similar role in the cat's brain. Release of acetylcholine from the mesolimbic cholinergic terminals distributed predominantly along the medial limbic structures, causes a dose dependent postsynaptic inhibition of neuronal firing. It is postulated that this vast inhibitory response represents a trigger for the behavioural response and alarm or threatening vocalization.
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