The GABAergic midbrain system is involved in the control of sleep and temperature homeostasis in pigeons.

Abstract

formation of the caudal midbrain region. The pigeon and mammalian (cat) midbrain GABAergic systems are assumed to differ in structural and functional organization. This study was performed with five adult pigeons ( Columba livia ) weighing 350‐390 g under the conditions of free behavior. The birds were anesthetized with Nembutal (25 mg/kg body weight) seven to ten days before the experiments. During the experiment, each animal was placed into a climatic chamber at 21 ‐ 1i C with a 12-h photoperiod. The operation technique and computer recording (the SASR 8800 system; United States) of electroencephalograms, electrooculograms, electromyograms, electrocardiograms, brain temperature (hypothalamus), and skin temperature of the unfeathered part of the foot were previously described [3, 4, 7]. The data were analyzed at a 1-s epoch. Saline (0.5 μ l, control), muscimol (0.3‐0.5 μ g/0.3‐0.5 μ l, Serva), and a GABA A receptor antagonist bicuculline (0.5‐1.0 μ g/ 0.5 μ l, Sigma) were bilaterally administered through guide cannulae 10 to 15 min prior to switching off the light. Figure 1 shows the places of microinjections (atlas: [8]). The microinjections ( n = 48) were made into the following midbrain caudal regions: I, the ventrolateral region of the substantia grisea centralis (coordinates A2.25‐A2.75; L1.7‐1.9; H9.5; II, ventral to the substantia grisea centralis, including the locus coeruleus (A2.25‐2.75; L1.7‐1.9; H10.0‐10.5); III, the dorsolateral region of the substantia grisea centralis (A2.25‐2.75; L1.7‐1.9; H8.5‐9.0); IV, the reticular formation and ventral to region II, at the border of the nucleus reticularis pontis oralis (A2.25‐2.75; L1.7‐ 1.9; H11.0). I. After a 18 ‐ 2-min latent period, muscimol caused an increase (compared to the control) in the total SWS time and duration of the SWS episodes during four hours (Fig. 2). After administration of bicuculline at a dose of 1 μ g, the total PS time decreased for two to three hours. A muscimol-induced decrease in brain temperature was caused by a more significant (2.2-fold) temperature decrease in the SWS episodes and a lesser temperature increase in the wakefulness and PS episodes (4- and 1.4-fold, respectively). The muscimol hypothermic effect was, probably, caused by a reduced heat produc