Form and function of dorsal horn neurones with axons ascending the dorsal columns in cat.

Abstract

SUMMARY1. Extracellular and intracellular recordings were made from dorsal horn neurones sending their axons through the dorsal columns in cats anaesthetized with chloralose and paralysed with gallamine triethiodide.2. Seventeen neurones were injected with horseradish peroxidase through the intracellular micro-electrode, recovered from the histological material and shown to send their axons into the dorsal columns.3. The cells had axonal conduction velocities of 30-47 ms-1; excitatory receptive fields that usually showed multireceptive characteristics, often including input from sensitive mechanoreceptors in glabrous skin; a third of the sample had a marked subliminal fringe to the excitatory field; inhibitory fields were usually situated proximal to the excitatory field and contiguous with it.4. The cells were located in laminae III, IV and medial V. Dorsal cells had restricted dendritic trees that ascended in an essentially cylindrical volume of tissue through lamina II and often into I; cells intermediate in depth had more primary dendrites than the others, usually dorsally directed into lamina II, and a more extensive rostro-caudal development; deep, medial cells had dendritic trees that radiated extensively from the cell body but were restricted to the transverse plane. Two cells had axons that ascended the dorsolateral funiculus for a few mm before re-entering the dorsal horn, crossing it and reaching the dorsal columns. Collaterals were given offthe axons in the grey matter, in the dorsolateral funiculus and the dorsal columns.5. The form and function of the neurones are discussed.

Cutaneous excitatory and inhibitory input to neurones of the postsynaptic dorsal column system in the cat.

“…While a small minority of units with spatially separate excitatory fields has been previously reported among samples of unidentified dorsal horn neurones (Devor & Wall, 1976;Pubols & Goldberger, 1980;Brenowitz & Pubols, 1981) these have always been located on the most proximal areas of the limb. Indeed, apart from previous studies of this system in the chloralose-anaesthetized cat (Brown & Fyffe, 1981;Brown et al 1983), there are no reports of dorsal horn neurones with complex receptive fields of the type that have been observed for PSDC units with input from glabrous skin. Several previous studies of PSDC neurones in the pentobarbitone-anaesthetized cat have failed to detect inhibitory input (Uddenberg, 1968;Angaut-Petit, 1975;Lu et al 1983), but inhibitory fields have been reported in about half of a sample of PSDC neurones recorded in the chloralose-anaesthetized cat (Brown et al 1983).…”

“…Previous reports of the receptive field arrangements of PSDC neurones recorded in pentobarbitone-anaesthetized animals have stressed their similarity with neurones of the SCT (Uddenberg, 1968;Angaut-Petit, 1975;Lu et al 1983), while experiments on chloralose-anaesthetized animals suggest a considerably more complex receptive field organization (Brown & Fyffe, 1981 ;Brown et al 1983). The present observations confirm that the majority of PSDC neurones, at least in the chloralose-anaesthetized preparation, have complex receptive fields which differ in their organization from those of identified neurones of the SCT (Hongo, Jankowska & Lundberg, 1968;Brown & Franz, 1969;Brown, Koerber & Noble, 1987).…”

“…Previous reports have largely been confined to units with receptive fields located on the distal 501 R. NOBLE AND J. S. RIDDELL regions of the limb, most of which included areas of glabrous skin (Brown & Fyffe, 1981;Brown et al 1983). The present study has extended these observations to include neurones with receptive fields on more proximal regions of the hindlimb and confined to the hairy skin.…”

“…However, recent work has shown that the PSDC and SCT systems arise, at least in substantial part, from separate populations of neurones in the dorsal horn (Brown, Noble & Riddell, 1986). Furthermore, studies of the morphology (Brown, Rose & Snow, 1977;Brown & Fyffe, 1981; Enevoldson, 1982) and ultrastructure of neurones of the two systems have revealed important differences between them. PSDC neurones are contacted by boutons which may participate in axo-axonic contacts, triadic arrangements and glomerular complexes (Maxwell, Koerber & Bannatyne, 1985; (Bannatyne, Maxwell & Brown, 1987), suggesting that both their course and fine fibre inputs are subject to presynaptic modulatory influences.…”

“…For PSDC neurones recorded in the chloralose-anaesthetized cat, some differences have already been noted (Brown & Fyffe, 1981;Brown, Brown, Fyffe & Pubols, 1983); but these studies involved relatively small samples of units, most of which had distally located receptive fields on the foot or toes. In the experiments to be reported in the present paper we have investigated the receptive field arrangements of a larger sample of identified PSDC units including those with receptive fields on proximal regions of the limb.…”