The smoke reflex in rabbits an example of autonomic control of cardiorespiratory function

This study was undertaken to elucidate aspects of autonomic behavior as reflected in the “smoke reflex” in rabbits. Allowing smoke to envelop the nostrils of a rabbit resulted in prompt apnea, bradycardia, diminution of peripheral pulse and elevation of systemic blood pressure. Atropine and vagotomy, or both, mitigated the bradycardia, but the combined effect of propranolol and vagotomy was required to abolish bradycardia. Phenoxybenzamine (dibenzyline) alone blocked only the peripheral vasoconstriction and pressor response. The combination of vagotomy, propranolol and phenoxybenzamine blocked all manifestations of the reflex with the exception of apnea. A classical concept holds that responses of the autonomie nervous system must be either distinctly adrenergic (sympathetic) or cholinergic (parasympathetic), and that visceral regulation is achieved by an antagonism between the two. This study introduces contrary evidence and demonstrates that in certain adaptive behavior there is a patterned response that includes activation of discrete elements of both cholinergic and adrenergic divisions, as well as inhibition of one component of the latter.