Receptive field organization and response properties of spinal neurones with axons ascending the dorsal columns in the cat.

Abstract

SUMMARY1. Micro-electrode recordings were made from single post-synaptic axons in the dorsal columns of cats anaesthetized with chloralose and paralysed with gallamine triethiodide. The recordings were made from the L5 segment and the axons were shown to project to the upper cervical level.2. Forty-eight units were recorded and the axons had conduction velocities of 22-61 ms-1, averaging 38-3 ms-1.3. Excitatory receptive fields were complex in many units, being made up of clearly defined, separate, low and high threshold areas. The receptive fields were often discontinuous. Only a few units behaved as if they received excitatory input from a single class of mechanoreceptors. A minority (13 %) of units had labile, excitatory receptive fields that expanded in size during the recording period.4. About 40 % of the units had inhibitory receptive fields. These were of two main types: either small and within or adjacent to the excitatory field, or large and separated from or adjacent to the excitatory field. 5. The great majority of units had resting discharges upon isolation and these consisted of single impulses or bursts of impulses at short intervals separated by longer, irregular periods.6. The time course of inhibition produced by electrical stimulation of cutaneous nerves suggested presynaptic inhibitory components to the inhibition. Some inhibitory curves were very prolonged with maxima at about 100 ms and total durations of up to 400 ms.7. The complexity of the receptive field organization in these dorsal horn neurones is discussed, as is their possible significance as input neurones to the dorsal column nuclei.

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).…”

“…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). The present results confirm that a large proportion (75 %) of PSDC neurones, at least in the chloralose-anaesthetized cat, have inhibitory receptive fields on the ipsilateral limb.…”

“…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.…”

“…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.…”