SLEEP STATE EFFECTS ON NONPANTING BREATHING DURING PREOPTIC ANTERIOR HYPOTHALAMIC WARMING IN CATS AND KITTENS/

Hypothalamic warming induces panting in cats; in young kittens, pantin g is interspersed with slower breathing periods. The nature of neural mechanisms underlying these interspersed periods of nonpanting polypne a is unclean. We determined developmental characteristics of nonpantin g breathing during thermal stress in kittens and adult cats. Warming e lectrodes were surgically placed into the preoptic/anterior hypothalam us (POAH) of 19 kittens and six adult cats. After surgical recovery, t he hypothalamus was warmed bilaterally during sleep in unrestrained an imals. Epochs of nonpanting breathing during periods of POAH warming w ithin quiet sleep (QS) and rapid eye movement sleep (REM) were compare d to control periods. Nonpanting polypnea within QS showed inspiratory and expiratory time reductions in the same proportions as those of pa nting. During REM, increased breathing rates accompanied POAH warming, but inspiratory/expiratory timing characteristics did not differ sign ificantly from those of baseline breathing, except in the youngest kit tens. Breathing responses to POAH warming during QS showed significant change as the kittens matured; however, response characteristics duri ng REM did not change significantly from 12 days to adulthood. Respons es to thermal stress during QS appear to depend on maturation of neura l mechanisms, while separate mechanisms appear to underlie the slight respiratory rate changes during REM.