RESPIRATORY RESPONSES TO PREOPTIC ANTERIOR HYPOTHALAMIC WARMING DURING SLEEP IN KITTENS/

The preoptic/anterior hypothalamic (POAH) area of 12-48-day-old unanae sthetized, unrestrained kittens was warmed with a diathermic probe to assess respiratory responses to a central thermal challenge during sle ep. During quiet sleep (QS), warming of the POAH by 1.4-3.8 degrees C induced periods of tachypnoea (panting) interspersed with periods of s lower respiration; the percentage of time spent in panting increased a s the kittens matured. During rapid eye movement (REM) sleep, POAH war ming induced a much smaller increase in respiratory rate and no sustai ned panting. Analysis of the dynamics of panting (in QS only, since pa nting did not occur in REM) revealed several changes from breathing pa tterns of normal respiration. During panting, the increased respirator y rate did not result from equal changes in inspiratory and expiratory times; inspiratory times accounted for a larger portion of the declin e in total respiratory cycle time. Amplitude of diaphragmatic electrom yographic activity showed an age-dependent response to thermal panting , which resulted in age-dependent. changes in ventilation and inspirat ory drive. The interspersion of slower with faster respiratory rates s uggests a competition of thermoregulatory and respiratory homeostatic mechanisms. The age-dependent ventilatory responses to thermal panting suggest greater vulnerability to thermal stress at particular ages, a nd may have implications for the sudden infant death syndrome.