DIFFERENTIAL ASCENDING PROJECTIONS FROM NEURONS IN THE CATS LATERAL CERVICAL NUCLEUS

Extracellular microelectrode recordings were made from single cells of the lateral cervical nucleus (LCN) in cats anaesthetized with chloral ose and paralysed with gallamine triethiodide. The cells were tested f or antidromic activation from the contralateral medial lemniscus and t he contralateral tectum. Seventy-two LCN units were recorded which pro jected to one or both targets. Sixty (83%) projected through the media l lemniscus, and of these 36 (50% of the total) also projected to the tectum, whereas 24 (33%) projected through the medial lemniscus only; 12 (17%) projected only to the tectum. Twenty-nine units (40%) were ex cited by moving hairs of the coat but not by pinch of the skin, and 9 (31%) of these projected to the tectum, 11 (38%) through the medial le mniscus and 9 (31%) to both targets. Forty units (56%) were excited by hair movement and noxious pinch, and 3 (7%) of these projected to the tectum, 10 (25%) through the medial lemniscus and 27 (68%) to both ta rgets. Three units (4%) had no discernible receptive fields and they a ll projected through the medial lemniscus, but not to the tectum. Of t he 12 units projecting only to the tectum, 11 had receptive fields com pletely or partially on the trunk. Units projecting either through the medial lemniscus only, or through the medial lemniscus and also into the tectum, had receptive fields more widely distributed: these includ ed small fields on the fore- and hind feet, on the limbs and also, a m inority, on the trunk. Units with glove- or stocking-like receptive fi elds projected through the medial lemniscus. The results show that whi le most LCN cells project through the medial lemniscus, those excited by hair movement alone preferentially project either to the tectum or through the medial lemniscus, but not by both routes. The differences in receptive field properties of the differently projecting units are discussed in terms of the possible functions of the spinocervical syst em.