Input from ipsilateral proprio- and exteroceptive hind limb afferents to nucleus Z of the cat medulla oblongata.

1. Extracellular recordings have been made from proprio- and exteroceptive neurones in nucleus Z of the cat medulla oblongata. 2. Seventeen non-relay cells were excited by ipsilateral hind limb group I muscle afferents. Their functional were similar to those of the corresponding relay cells (Johansson & Silfvenius, 1977), i.e. activation by axon-collaterals of dorsolateral fascicle (DLF) fibres was observed, indicative of an input from the dorsal spinocerebellar tract (DSCT) to these neurones. The non-relay cells differed, however, from the relay cells in that a larger proportion of them were disynaptically connected to the spinal fibres. It is suggested that the non-relay cells by inhibition modulate the group I relay transmission in nucleus Z. 3. Fifteen cells were excited by ipsilateral hind limb low threshold skin afferents with their spinal fibres at the first cervical segment located either in the DLF or in the dorsal column (DC). Evidence for a cutaneous hind limb bulbothalamic path independent of that of the DC and of the spinocervicolemniscal path is presented. 4. Six cells were activated by ipsilateral hind limb joint afferents at low threshold. At the C1 level the spinal fibres were located either in the DLF or in the DC. No joint activated relay-cells were encountered. Axon-collateral activation of DLF-linked joint cells was observed during cerebellar stimulation, indicating that segmental DSCT cells mediated the joint input to nucleus Z. 5. The topographical organization within nucleus Z and its input relation to the DSCT is discussed.