Functional organization of the sympathetic innervation supplying the hairless skin of the hindpaws in chronic spinal cats

Abstract

• 1. Reflex activation of the sudomotor system supplying the cat's hindpaws to natural stimulation of skin has been investigated in chronic low thoracic spinal cats. The neuronal activation of the sweat glands was measured by recording the skin potentials from the surface of the hairless skin.

• 2. The sudomotor system was activated by mechanical and thermal noxious stimulation of skin and by stimuli which excited the Pacinian corpuscles in the paws. The reflexes were maximal some 50 to 75 days following spinalization.

• 3. Noxious stimulation of the skin was followed by an increase of the size and of the frequency of the resting activity in the sudomotor system. This increase of the resting activity lasted for 10 min or longer and was, in many preparations, especially pronounced 40 days or later after spinalization.

• 4. Neurophysiological investigations of postganglionic neurones in the medial plantar nerve in 10 chronic spinal cats (74 to 129 days after spinalization) revealed two populations of postganglionic neurones:type 1 neurones were excited by noxious cutaneous stimuli and by vibrational stimuli and classified as sudomotor neurones.Type 2 neurones were inhibited by noxious cutaneous stimuli applied to the ipsilateral hindfoot and mostly excited by noxious stimuli applied to the contralateral hindfoot and not affected by vibrational stimuli. These neurones were classified most likely as vasoconstrictor neurones.

• 5. The results argue that the chronic spinal cord contains reflex circuits relaying specific somatosympathetic reflexes to the sweat glands. Whether these spinal circuits are normally used in cats with intact CNS is an open question.