Functional organization in nucleus gracilis of the cat

Abstract

The dorsal column nuclei (nucleus cuneatus and nucleus gracilis), receiving many primary afferent fibres from the dorsal columns and sending many secondary fibres into the medial lemniscus, might be expected to be interesting in that they could contribute to the central analysis of sensory information. These nuclei appear to have a high factor of safety in transmission, as judged by the work of Therman (1941), who studied their function as 'relays'. More recently, it has been suggested that they contain paths that are not purely monosynaptic and that their organization is therefore more complex than that of simple relays; and limited spatial facilitation and inhibition of single neurones have been described (Amassian & de Vito, 1957).We have approached this problem from the point of view of the way or ways in which impulses set up by combinations of tactile stimuli are handled by these nuclei, bearing in mind that such phenomena as mutual spatial inhibition have been seen in other primary sensory nuclei-in the visual and auditory pathways, for instance-and are likely to be relevant in sensory discrimination. We have therefore been concerned particularly with the cutaneous receptive areas of the cells and with spatial interactions, whether facilitatory or inhibitory, upon these cells. We have largely confined ourselves to those cells in nucleus gracilis which responded to tactile stimulation of the hind foot. A preliminary communication on this subject has already been made (Gordon & Paine, 1959). METHODSPreparation and fixation of animaws. Cats were used for all the experiments. The great majority were anaesthetized with sodium pentobarbitone, the initial dose given intraperitoneally (38 mg/kg) and subsequent small doses of about 10 mg given by intravenous cannula. Anaesthesia was maintained at a Jevel sufficient to prevent any spontaneous movement of the animal or movement in response to stimulation. A few animals were decerebrated under ether by blunt section at intercollicular level; and at some stage after recovery from the anaesthetic it was always necessary to prevent movement in these animals, e.g. by giving 1 mg doses of decamethonium iodide intravenously, respiration being maintained with a pump.

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

“…Surround inhibition has also been described for neurones at other stages in the dorsal column system: in the dorsal column nuclei (Gordon & Jukes, 1964;Andersen, Etholm & Gordon, 1970;Bystrzycka, Nail & Rowe, 1977;Aoki, 1981); the thalamus (Poggio & Mountcastle, 1963;Gordon & Manson, 1967;Baker, 1971;Janig, Spencer & Younkin, 1979) and in the somatosensory cortex (Mountcastle & Powell, 1959;Baker, Tyner & Towe, 1971;Laskin & Spencer, 1979). It has generally been considered to provide a mechanism for improving spatial discrimination of tactile stimuli (Mountcastle & Powell, 1959;Gordon & Paine, 1960;Andersson, 1962).…”

On the pharmacology of the γ‐aminobutyric acid receptors on the cuneo‐thalamic relay cells of the cat

“…Postsynaptic hyperpolarization is invariably accompanied by an increased excitability of the appropriate primary afferents. Pre-and postsynaptic mechanisms operating concurrently may well account for the inhibition of cuneate relay cells by a recurrent input from the ipsilateral medial lemniscus (Gordon & Paine, 1960; Gordon & Seed, 1961;Gordon & Jukes, 1964), contralateral inputs from the medial and sural nerves (Jabbur & Banna, 1968 and the pyramidal tract (Magni, Melzack, Moruzzi & Smith, 1959;Jabbur & Towe, 1961;Levitt, Carreras, Liu & Chambers, 1964;Andersen et al, 1964b;Andersen, Eccles, Oshima & Schmidt, 1964a).…”

Neurones in cat gracile nucleus with both local and widefield inputs.

“…Cells with receptive fields over the whole of a limb or encompassing more than one limb have occasionally been reported in the gracile nucleus of the cat (Gordon & Paine, 1960;Kruger, Siminoff & Witkovsky, 1961;Perl, Whitlock & Gentry, 1962;Winter, 1965), but when studied with mechanical stimuli, the cells appeared to have much the same threshold over the whole receptive field. We believe that the present results are the first to show that gracile cells may have two distinct components to their receptive field.…”

“…In the main, or 'cell cluster' part of the nucleus (Kuypers & Tuerk, 1964) extending from the obex approximately 4-5 mm caudally (Gordon & Paine, 1960) the neurones are considered to have spatially discrete, topographically organized receptive fields (Millar & Basbaum, 1975). A small proportion respond to limb movement, partly due to the activity of joint afferents (Williams, Dement, Yin & McCall, 1973), and some respond to noxious stimulation (Angaut-Petit, 1975).…”