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- BARTHE, JY, et al.
(författare)
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Neurotensin-induced modulation of spinal neurons and fictive locomotion in the lamprey
- 1995
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 73:3, s. 1308-1312
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Tidskriftsartikel (refereegranskat)abstract
- 1. Neurotensin containing interneurons are present in the spinal cord of both mammalian and nonmammalian vertebrates, but as yet little is known about their functional role. In this study we examine the effect of neurotensin on spinal cells and on the central pattern generator for locomotion in the lamprey spinal cord. 2. Bath application of neurotensin (10(-8) to 10(-6) M) slowed down the fictive locomotor activity induced by the glutamate agonist N-methyl-D-aspartate in the isolated spinal cord. The duration of the bursts of activity in the ventral roots increased in proportion to the increase of the locomotor cycle duration. 3. Intracellular recordings from grey matter neurons and intraspinal stretch receptors neurons showed that neurotensin induced a depolarization [4.4 +/- 0.5 (SE) mV, n = 19]. This depolarization could still be obtained after a blockade of voltage-sensitive sodium channels with tetrodotoxin (1.5 +/- 0.5 mV; n = 6), and after removal of calcium (2.8 +/- 0.4 mV; n = 5). Moreover no consistent change occurred in the fast and slow phase of the afterhyperpolarization (AHP) both of which are carried by potassium currents.
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| 2. |
- Vinay, L, et al.
(författare)
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Central modulation of stretch receptor neurons during fictive locomotion in lamprey
- 1996
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Ingår i: Journal of neurophysiology. - : American Physiological Society. - 0022-3077 .- 1522-1598. ; 76:2, s. 1224-1235
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Tidskriftsartikel (refereegranskat)abstract
- 1. In lamprey, stretch receptor neurons (SRNs), also referred to as edge cells, are located along the lateral margin of the spinal cord. They sense the lateral movements occurring in each swim cycle during locomotion. The isolated lamprey spinal cord in vitro was used to investigate the activity of SRNs during fictive locomotion induced by bath-applied N-methyl-D-aspartate (NMDA). Intracellular recordings with potassium acetate filled electrodes showed that 63% of SRNs had a clear locomotor-related modulation of their membrane potential. 2. Of the modulated SRNs, two-thirds had periods of alternating excitation and inhibition occurring during the ipsilateral and the contralateral ventral root bursts, respectively. The phasic hyperpolarization could be reversed into a depolarizing phase after the injection of chloride ions into the cells; this revealed a chloride-dependent synaptic drive. The remaining modulated SRNs were inhibited phasically during ipsilateral motor activity. 3. Experiments with barriers partitioning the recording chamber with the spinal cord into three pools, allowed an inactivation of the locomotor networks within one pool by washing out NMDA from the pool in which the SRN was recorded. This resulted in a marked reduction, but not an abolishment, of the amplitude of the membrane potential oscillations. Both the excitatory and the inhibitory phases were reduced, resulting from removal of input from inhibitory and excitatory interneurons projecting from the adjacent pools. If the glycine receptor antagonist strychnine (1 microM) was applied in one pool, the phasic hyperpolarizing phase disappeared without affecting the excitatory phase. 4. Bath application of the gamma-aminobutyric acid (GABA)A receptor antagonist, bicuculline (50-100 microM) blocked the spontaneous large unitary inhibitory postsynaptic potentials, which occurred without a clear phasic pattern. Bicuculline had no significant effect on the peak to peak amplitude of the locomotor-related membrane potential oscillations. The inhibition in SRNs therefore has a dual origin: glycinergic interneurons provide phasic inhibition, while the GABA system can exert a tonic inhibition via GABAA receptors. 5. These data show that, in addition to the stretch-evoked excitation, which SRNs receive during each locomotor cycle, most of them also receive excitation from the central pattern generator network during the ipsilateral contraction, which may ensure a maintained high level of sensitivity to stretch during the shortening phase of the locomotor cycle. This arrangement is analogous to the efferent control of muscle spindles exerted by gamma-motoneurons in mammals, which as a rule are coactivated with alpha-motoneurons to the same muscle (alpha-gamma linkage).
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