Brainstem control of shivering in the cat. II. Facilitation.

Regions containing areas and pathways mediating heat gain responses in the mesencephalon and upper pons and in the medulla were studied using topical microinjection of a local anesthetic. These facilitatory areas and pathways were compared in the decerebrated and intact cats. In lower pontine preparations shivering was abolished by bilateral injections of procaine into the lateral medullary reticular formation. Injections into the same areas in the intact anesthetized cat resulted in the cessation of shivering. These effects on facilitatory areas are reversible and can be repeated in the same preparation several times. Permanent effects were obtained by electrolytic lesions or by the local microinjections of 1% osmic acid. In summary it shown, by means of microinjection of local anesthetic, that the pathways mediating shivering in the intact and lower pontine cats are located in the same area in lateral reticular formation of pons and medulla.