Abstract
1. Extracellular microelectrode recordings were made from projection neurones of the lateral cervical nucleus (LCN) in cats anaesthetized with chloralose and paralysed with gallamine triethiodide. 2. The receptive fields of eight-five units were analysed. Most units had excitatory receptive fields similar in size and shape to those of spinocervical tract (SCT) cells. A few (14%) had either very large fields or 'stocking-like' fields. The majority of the LCN neurones (fifty-five, 65%) were excited by hair movement and, in addition, by noxious mechanical stimulation within the skin area responding to hair movement. Twenty-five units (29%) were excited by hair movement alone. For seven of these twenty-five neurones, noxious mechanical stimulation within the excitatory receptive field produced inhibition of the background discharge. One unit was excited by noxious mechanical stimulation and for the remaining four units no receptive field could be found. In six units inhibitory receptive fields outside the excitatory field were found. 3. Air-jet stimuli were used to define the excitatory profiles of the units' receptive fields to hair movement. In general, receptive fields had single regions of greatest sensitivity usually at or near the centre of the field, where that was oval in shape, with the sensitivity declining towards the field's circumference. In some units with very large fields that included parts of one or two limbs and the trunk there could be more than one highly sensitive region. 4. Pairs of air-jet stimuli were used to investigate in-field afferent inhibition in LCN cells. One jet was used to condition the responses to another jet located at a different position within the excitatory receptive field and occurring 200 ms later. Sixteen units were tested and significant in-field inhibition was observed in all sixteen. 5. The in-field afferent inhibition was organized spatially in the sense that inhibition was generally strongest when the conditioning and testing stimuli were close together and became weaker as they were moved apart. The afferent inhibition was not simply a function of the response produced by the conditioning stimulus. Furthermore, increasing the strength of the stimuli did not in general lead to larger areas from which the inhibition could be produced. The inhibitory areas defined in these experiments were generally less than 120 mm in length in units with receptive fields much longer than 100 mm.(ABSTRACT TRUNCATED AT 400 WORDS)