Showing papers on "Cuneate nucleus published in 1969"

Afferent connexions to group I activated cells in the main cuneate nucleus of the cat.

Abstract: 1. Extracellular recordings were made from a total of 240 group I activated cells in the main cuneate nucleus. Cuneothalamic relay neurones (128) were identified by antidromic stimulation of the medial lemniscus in the ventrobasal thalamic complex. 2. A majority of the relay neurones were activated by afferents in only one of six dissected forelimb nerves innervating muscle groups at various joints. Even among afferents from adjacent synergistic muscles, convergence to individual neurones was infrequent. 3. Some of the relay neurones received excitation from group II muscle afferents in the same nerve that provided group I excitation. Excitation from group II muscle afferents in other nerves was uncommon. Some neurones were weakly excited by cutaneous volleys. 4. Inhibition of group I relay cells was produced from cutaneous afferents and group II muscle afferents. Weak inhibition was sometimes observed from group I afferents. The relay cells were also inhibited by stimulation of the cerebral cortex with a focus around the lateral end of the cruciate sulcus. A good correspondence was found between the inhibition and the depolarization of group I afferent terminals in the cuneate nucleus. 5. A majority of the group I activated cells not antidromically activated from the ventrobasal complex (`non-relay cells') were excited by cortical stimulation. Excitation from cutaneous afferents and group II muscle afferents was frequently found among these cells. 6. The group I activated cells were found almost exclusively in the ventral part of the nucleus. 7. The pattern of convergence found in eleven group I activated cells in the dorsal horn of the spinal cord from C 2 to C 4 is described.

Effects of procaine, pentobarbital and halothane on synaptic transmission in the central nervous system

Abstract: Experiments were performed in the cuneate nucleus of decerebrate cats to study the effect of procaine, pentobarbital and halothane on pre- and postsynaptic structures. Pentobarbital and procaine, as well as other relevant compounds, were given by microiontophoresis using five-barrelled glass pipettes. Pentobarbital and halothane were also given systemically or by superfusion of the nucleus. Cuneate neurons were identified as relay units and interneurons, or according to their response to specific stimuli (touch, hair, joint). The results are consistent with the idea of multiple mechanisms of action responsible for the depression of synaptic transmission observed during the administration of anesthetics. Procaine depressed excitability of pre- and postsynaptic elements in a nonspecific way. Pentobarbital appeared more effective in depressing postsynaptic excitation. Halothane depressed synaptic transmission through the cuneate nucleus but had no significant effect on either pre- or postsynaptic structures.

Effects of micro-iontophoretic administration of magnesium and calcium on neurones in the central nervous system of cats

Abstract: Ca2+ and Mg2+ released from five-barrelled micropipettes by currents of 5 to 80 nA caused a deceleration of the firing rate of neurones discharging spontaneously, or excited by the simulataneous administration of glutamate or acetylcholine, in the cerebral cortex, cuneate nucleus and spinal cord. Excitation of cells in the cuneate nucleus, caused by stimulation of sense organs, was also suppressed by Ca2+ and Mg2+. Synaptic transmission of volleys, evoked by electrical stimulation, from thalamus to cortical cells, from superficial radial nerve to cells in the cuneate nucleus, and from ventral root via recurrent collaterals to Renshaw cells, was partially or completely blocked by Ca2+ and Mg2+ (60 to 200 nA). When given together, the depressant effect of the two ions summed. There was no evidence of enhanced synpatic transmission under the influence of Ca2+. It is concluded that in the central nervous system a small elevation of the concentration of Ca2+ or of Mg2+ has a powerful postsynaptic depressant effect.

The effects of respiratory acidosis on a sensory relay system

Abstract: The effects of hypercarbia on afferent inputs and synaptic transmission in the cuneate nucleus were studied in decerebrate cats. Stimulation with microelectrodes placed in the cuneate nucleus and/or dorsal column evoked antidromic potentials in the superficial radial nerve; stimulation of afferent fibres in the forelimb, dorsal column, or cuneate nucleus evoked orthodromic responses in the medial lemniscus. Small increases of inspired C02 ( ≦ 5% ) often increased synaptic transmission and the excitability of afferent fibres. Further increases of Pco2 depressed transmission and terminal excitability, while producing considerably smaller changes in postsynaptic excitability. CO2 had no obvious effect on the inhibition of orthodromic transmission produced by afferent nerve interaction, but markedly depressed the dorsal column reflexes. The efficiency of synaptic transmission, as estimated from the input-output relation of the cuneate, was maintained at individual active synapses. It is suggested that C02 does not depress release of transmitter at this synapse, and that the changes in transmission are effected mainly by presynaptic events, possibly by block of conduction in the intraspinal afferent fibres and/or their terminals.