The sensitivity to glutamate of denervated muscles of the crayfish

Abstract

SUMMARYThe effect of denervation on the sensitivity of muscle fibres to glutamate was studied in leg muscles of crayfish.1. When the motor nerve was cut close to the proximal accessory flexor muscle the distal end of the nerve degenerated. Neuromuscular transmission failed and spontaneous miniature potentials disappeared after two months. Several stages of nerve terminal degeneration were seen in muscles denervated between 1 and 3 months, and after 4 months no remains of synapses could be found. 2. Following denervation for periods up to 8 months there was no significant change in sensitivity to glutamate, a substance that mimics the action of the neural transmitter. Depolarizations produced by various concentrations of glutamate in the bathing solution were the same in denervated and control muscle fibres. Moreover, the sensitivity to iontophoretically applied glutamate was localized to discrete patches as in innervated muscles.3. Supersensitivity of muscles apparently does not occur after denervation in the crayfish.

Glutamate sensitivity and distribution of receptors along normal and denervated locust muscle fibres.

“…It therefore seems possible that glutamate-sensitive central neurones may also develop increased sensitivity to glutamate following denervation. However, it should be noted that no change in glutamate sensitivity has been found in crayfish muscle, even after prolonged denervation and subsequent degeneration of nerve terminals (Frank, 1974).…”

Glutamate sensitivity and distribution of receptors along normal and denervated locust muscle fibres.

“…It therefore seems possible that glutamate-sensitive central neurones may also develop increased sensitivity to glutamate following denervation. However, it should be noted that no change in glutamate sensitivity has been found in crayfish muscle, even after prolonged denervation and subsequent degeneration of nerve terminals (Frank, 1974).…”

Further Observations on the Interaction Between Gluta Mate and Aspartate on Lobster Muscle

“…Intact muscle fibres in such preparations had resting potentials and membrane resistances in the control range (about -76 mV; 50 kQ respectively) and showed the usual sensitivity to depolarizing agonists (cf. Frank, 1974). However, the initially large response given by aspartate at the beginning of experiments was now absent, and a plateau response level was attained after fewer repeated applications of aspartate; the enhancement of aspartate responses after conditioning with agonists was not noticeably affected.…”

Strengthening of synaptic contacts of an excitatory axon on elimination of a second excitatory axon innervating the same target

“…But the observations that the field of innervation shrinks within a few days if the axon is cut, and that the rate of release decreases in the remaining terminals are interesting per se. Although the peripheral portion of the axon, without connection to the cell body, will survive for months, conduct action potentials, and maintain functional synapses (Hoy et al, 1967;Bittner and Johnson, 1974;Frank, 1974), the release at the terminals is much lower than when they are connected to the cell body. Therefore, it appears that a central factor or cofactor may control the function or the growth of terminals.…”

Glutamate sensitivity and distribution of receptors along normal and denervated locust muscle fibres.

“…It therefore seems possible that glutamate-sensitive central neurones may also develop increased sensitivity to glutamate following denervation. However, it should be noted that no change in glutamate sensitivity has been found in crayfish muscle, even after prolonged denervation and subsequent degeneration of nerve terminals (Frank, 1974).…”

Further Observations on the Interaction Between Gluta Mate and Aspartate on Lobster Muscle

“…Intact muscle fibres in such preparations had resting potentials and membrane resistances in the control range (about -76 mV; 50 kQ respectively) and showed the usual sensitivity to depolarizing agonists (cf. Frank, 1974). However, the initially large response given by aspartate at the beginning of experiments was now absent, and a plateau response level was attained after fewer repeated applications of aspartate; the enhancement of aspartate responses after conditioning with agonists was not noticeably affected.…”

Strengthening of synaptic contacts of an excitatory axon on elimination of a second excitatory axon innervating the same target

“…But the observations that the field of innervation shrinks within a few days if the axon is cut, and that the rate of release decreases in the remaining terminals are interesting per se. Although the peripheral portion of the axon, without connection to the cell body, will survive for months, conduct action potentials, and maintain functional synapses (Hoy et al, 1967;Bittner and Johnson, 1974;Frank, 1974), the release at the terminals is much lower than when they are connected to the cell body. Therefore, it appears that a central factor or cofactor may control the function or the growth of terminals.…”

Glutamate sensitivity and distribution of receptors along normal and denervated locust muscle fibres.

“…It therefore seems possible that glutamate-sensitive central neurones may also develop increased sensitivity to glutamate following denervation. However, it should be noted that no change in glutamate sensitivity has been found in crayfish muscle, even after prolonged denervation and subsequent degeneration of nerve terminals (Frank, 1974).…”

Further Observations on the Interaction Between Gluta Mate and Aspartate on Lobster Muscle

“…Intact muscle fibres in such preparations had resting potentials and membrane resistances in the control range (about -76 mV; 50 kQ respectively) and showed the usual sensitivity to depolarizing agonists (cf. Frank, 1974). However, the initially large response given by aspartate at the beginning of experiments was now absent, and a plateau response level was attained after fewer repeated applications of aspartate; the enhancement of aspartate responses after conditioning with agonists was not noticeably affected.…”

Strengthening of synaptic contacts of an excitatory axon on elimination of a second excitatory axon innervating the same target

“…But the observations that the field of innervation shrinks within a few days if the axon is cut, and that the rate of release decreases in the remaining terminals are interesting per se. Although the peripheral portion of the axon, without connection to the cell body, will survive for months, conduct action potentials, and maintain functional synapses (Hoy et al, 1967;Bittner and Johnson, 1974;Frank, 1974), the release at the terminals is much lower than when they are connected to the cell body. Therefore, it appears that a central factor or cofactor may control the function or the growth of terminals.…”