Acta physiol. scand. 1975. 94. 177-183 From the Departments of Physiology and Physics, University of Oslo, Norway
Reflex Inhibition of the Slowly Adapting Stretch Receptors in the Intact Abdomen of the Crayfish BY A. NJA and L. WALL0E Received 19 December 1974
- Abstract
NJA, A. and L.
WALL0E. Reflex inhibition of the slowly adapting stretch receptors in the intact abdomen of’ the crayfish. Acta physiol. scand. 1975. 94. 177-183.
The reflex inhibition of abdominal stretch receptors in crayfish was studied by controlled passive flexion of individual abdominal joints. The results are very similar to those obtained by electrical or mechanical stimulation of individual stretch receptors in immobilized abdomens. Reflex effects from posterior to anterior abdominal segments are somewhat stronger than in the opposite direction. Flexion of one abdominal joint excites the stretch receptors of that joint and inhibits the stretch receptors in neighbouring abdominal segments. Without reflex inhibition flexion of one abdominal joint excites the stretch receptors in several abdominal segments.
The slowly adapting stretch receptors in the thorax and abdomen of the crayfish have provided unusual opportunities for the investigation of sensory inhibition. The histology of the receptors and their efferent innervation has been described in lobster and crayfish (Alexandrowicz 1951, 1952, 1967, Florey and Florey 1955). The peripheral cell body, attached to a specialized muscle strand, facilitates isolation of functioning receptors and allows adequate activation by stretch applied to the muscle strand, application of various solutions, stimulation of inhibitory axons, and recording of synaptic potentials and injection of currents with an intracellular microelectrode. These technical advantages have made possible detailed studies on the inhibitory synaptic mechanisms and transmitter action of the large accessory neuron, which is the main inhibitory axon (Kuffler and Eyzaquire 1955, Hagiwara, Kusano and Saito 1960). There is one slowly adapting stretch receptor and one large accessory neuron on each side of each abdominal segment. When the neural connections between the receptor and the central nervous system are intact, activity in one slowly adapting stretch receptor reflexly activates its own large accessory neuron. In addition, this receptor activates the large accessory neurons of several other abdominal segments, mainly on the same side of the animal (Eckert 1961). The distribution of this large accessory reflex to different abdominal segments and the input-output relations of the various reflex connections have been determined by electrical and mechanical stimulation of receptors in immobilized abdomens 12 - 755876
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(Eckert 1961, Jansen, Nja and Wallere 1970 b, Jansen, Njh, Ormstad and Wallere 1971 a, b). Page and Sokolove (1972) recently published a report which emphasized the non-symmetrical distribution of the reflex. They found considerably stronger reflex connection from posterior to anterior segments than in the opposite direction when receptors were activated by spontaneous or command-fibre induced abdominal flexions. The asymmetry of the reflex coupling is small during electrical stimulation of the stretch receptor axons (Jansen et al. 1970 b). Because of this discrepancy, we investigated the input-output relations of the large accessory reflex during controlled passive flexion of individual abdominal joints. The pattern of stretch receptor activation thus obtained has several distinctive features: (1) Simultaneous and equally strong activation of stretch receptors on both sides of the animal. (2) Selective activation of slowly adapting stretch receptors, because the rapidly adapting receptors respond only to full range flexions of high velocity (Njh and Wallere 1973). (3) Possible activation of other kinds of receptors with reflex connections to the large accessory neurons. To understand the in situ performance of the large accessory reflex, results which have been obtained by electrical and mechanical stimulation of the receptors of immobilized abdomens should be supplemented by experiments in which the receptors are activated by joint flexion. In this report we show that the reflex activation produced by passive joint flexion in intact abdomens is very similar to that produced by direct electrical or mechanical stimulation of the receptors.
Methods The experiments were performed o n the isolated abdomen of fresh water crayfish (Astacus fluuiatilw). The preparations were bathed in oxygenated saline containing (mM): NaCl 205, KC1 5.4, CaCI, 13.5, MgCI, 2.6, Tris 10; titrated.to pH 7.2 to 7.4 with maleic acid. The temperature of the bath was thermostatically controlled at 12°C. The stretch receptors were activated by controlled, passive flexion of the abdominal joints (Fig. I). Most of the experimental set-up and the technique for flexing the joints have been described earlier ( N j i and Wallee 1973). Action potentials were recorded extracellularly with flexible “suction electrodes” fitted into circular boreholes (Fig. 1). N o suction was needed, since the rubber coated electrode shaft stuck to the borehole after i t had been inserted as far as necessary to obtain good contact between electrode and nerve (branch of the second root innervating the extensor muscles). Situated close to the joint axis, the electrode-to-nerve contact was unaffected during the full range of movements in the joint. The amplifier activity was displayed on a cathode ray tube and photographed conventionally on moving film. Frequencies were counted over I s starting 0.5 s after the beginning of the step.
Fig. 1. Typical experimental arrangement. 3 simultaneous recordings are made from the right side of the second, third and fourth segments. Left: Zero reference position. Right: Selective flexion of the joint between the third and the fourth segments.
REFLEX INHIBITION OF STRETCH RECEPTORS
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Fig. 2. Reflex output from the large accessory neuron as a function of slowly adapting stretch receptor input. The stretch receptor o n the right side of the third segment was activated by pulling the receptor muscle with a fine glass hook (filled symbols) in between 2 series of fl-xion experiments (open symbols). Circlzs represent the reflex output i n the same segment and triangles the reflex output in the next anterior segment. Contralateral stretch receptors were denervated. Solid lines: First serizs of flexion experiments. Dashed lines: Second series of flexion experiments. and ipsilateral ( Q ) Fig. 3. Reflex output from the large accessory neuron E S a function of bilateral (0) slowly adapting stretch receptor input. The recording was made from the right side of the second segment during flexion. lpsilateral input was produced by denervation of the receptor on the opposite side. Two trials (solid and dashed lines) were performed in each situation.
In the experiments in which the reflex effects of pulling the receptor muscle were compared to those clicited by joint flexion, the dorsal part of the tergite of abdominal segments 2 , 3 and 4 were removed to expose the stretch receptors bilaterally. T he stretch receptors on the left side of these segments were denervated. The positions of the joints were controlled by means of pins inserted vertically through the animal on the left side, one in each segment from no. 2 through no. 5, instead of glass rods i n the midline.
Results Input-output relations of the large accessory reflex Impulse activity in a slowly adapting stretch receptor caused reflex activation of its own large accessory neuron. In addition, the large accessory neurons of several other abdominal segments were activated. Receptor activation by joint flexion produced the same reflex output as that produced by direct stretch of the receptor muscle strand, provided that the contralateral stretch receptor had been denervated. The results from one experiment are illustrated in Fig. 2, which shows the ipsilateral reflex outputs from the large accessory neurons in the same and neighbouring segments as a function of impulse frequency in the slowly adapting stretch receptor. There was no difference in the reflex output produced either by flexion or by direct mechanical activation of the receptor. 5 expts. on 4 animals all showed similar results. The effect of bilateral stretch receptor input was compared to that of unilateral input in several experiments. Ipsilateral input was obtained after cutting the nerve on the opposite side. Fig. 3 shows the results from a typical experiment. No difference occurred for most input frequencies. For input frequencies below about I5 imp/s, however, bilateral input was more effective than ipsilatera1 input.
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Fig. 4. Efficiency of the large accessory reflex couplings in the anterior and the oosterior directions. Data from 17 pairs of iarge accessory reflexes between neighbouring segments. The input frequency was 20 irnp/sec. A. The arrows represent the output frequencies in irnp/sec for the reflexes in the anterior (above the line) and the posterior (below the line) directions. B. Similar representation of the differences within pairs (anterior direction f posterior direction). Positive differences are shown above the line.
The distribution of this reflex to different abdominal segments is of obvious functional significance. Page and Sokolove (1972) recently published a report that emphasized the non-symmetrical distribution of the reflex. They found considerably stronger reflex connections from posterior to anterior segments than in the opposite direction and suggested that this could have important consequences in reflex function. We studied the symmetry of reflex coupling in 17 pairs of ipsilateral reflexes between neighbouring segments. In Fig. 4 A the reflex output (in imp/s) evoked by a stretch receptor input frequency of 20 imp/s is shown for each of the 34 reflexes. The difference between the output frequencies in the two directions appears to be small. The point estimate of the median of the output frequencies is 12 imp/s in the anterior direction and 9 imp/s in the posterior direction. The corresponding confidence intervals, with a confidence coefficient of 0.95, are 9 imp/s < q
Reflex Inhibition of the Slowly Adapting Stretch Receptors in the Intact Abdomen of the Crayfish BY A. NJA and L. WALL0E Received 19 December 1974
- Abstract
NJA, A. and L.
WALL0E. Reflex inhibition of the slowly adapting stretch receptors in the intact abdomen of’ the crayfish. Acta physiol. scand. 1975. 94. 177-183.
The reflex inhibition of abdominal stretch receptors in crayfish was studied by controlled passive flexion of individual abdominal joints. The results are very similar to those obtained by electrical or mechanical stimulation of individual stretch receptors in immobilized abdomens. Reflex effects from posterior to anterior abdominal segments are somewhat stronger than in the opposite direction. Flexion of one abdominal joint excites the stretch receptors of that joint and inhibits the stretch receptors in neighbouring abdominal segments. Without reflex inhibition flexion of one abdominal joint excites the stretch receptors in several abdominal segments.
The slowly adapting stretch receptors in the thorax and abdomen of the crayfish have provided unusual opportunities for the investigation of sensory inhibition. The histology of the receptors and their efferent innervation has been described in lobster and crayfish (Alexandrowicz 1951, 1952, 1967, Florey and Florey 1955). The peripheral cell body, attached to a specialized muscle strand, facilitates isolation of functioning receptors and allows adequate activation by stretch applied to the muscle strand, application of various solutions, stimulation of inhibitory axons, and recording of synaptic potentials and injection of currents with an intracellular microelectrode. These technical advantages have made possible detailed studies on the inhibitory synaptic mechanisms and transmitter action of the large accessory neuron, which is the main inhibitory axon (Kuffler and Eyzaquire 1955, Hagiwara, Kusano and Saito 1960). There is one slowly adapting stretch receptor and one large accessory neuron on each side of each abdominal segment. When the neural connections between the receptor and the central nervous system are intact, activity in one slowly adapting stretch receptor reflexly activates its own large accessory neuron. In addition, this receptor activates the large accessory neurons of several other abdominal segments, mainly on the same side of the animal (Eckert 1961). The distribution of this large accessory reflex to different abdominal segments and the input-output relations of the various reflex connections have been determined by electrical and mechanical stimulation of receptors in immobilized abdomens 12 - 755876
177
178
A. NJA AND L. WALL0E
(Eckert 1961, Jansen, Nja and Wallere 1970 b, Jansen, Njh, Ormstad and Wallere 1971 a, b). Page and Sokolove (1972) recently published a report which emphasized the non-symmetrical distribution of the reflex. They found considerably stronger reflex connection from posterior to anterior segments than in the opposite direction when receptors were activated by spontaneous or command-fibre induced abdominal flexions. The asymmetry of the reflex coupling is small during electrical stimulation of the stretch receptor axons (Jansen et al. 1970 b). Because of this discrepancy, we investigated the input-output relations of the large accessory reflex during controlled passive flexion of individual abdominal joints. The pattern of stretch receptor activation thus obtained has several distinctive features: (1) Simultaneous and equally strong activation of stretch receptors on both sides of the animal. (2) Selective activation of slowly adapting stretch receptors, because the rapidly adapting receptors respond only to full range flexions of high velocity (Njh and Wallere 1973). (3) Possible activation of other kinds of receptors with reflex connections to the large accessory neurons. To understand the in situ performance of the large accessory reflex, results which have been obtained by electrical and mechanical stimulation of the receptors of immobilized abdomens should be supplemented by experiments in which the receptors are activated by joint flexion. In this report we show that the reflex activation produced by passive joint flexion in intact abdomens is very similar to that produced by direct electrical or mechanical stimulation of the receptors.
Methods The experiments were performed o n the isolated abdomen of fresh water crayfish (Astacus fluuiatilw). The preparations were bathed in oxygenated saline containing (mM): NaCl 205, KC1 5.4, CaCI, 13.5, MgCI, 2.6, Tris 10; titrated.to pH 7.2 to 7.4 with maleic acid. The temperature of the bath was thermostatically controlled at 12°C. The stretch receptors were activated by controlled, passive flexion of the abdominal joints (Fig. I). Most of the experimental set-up and the technique for flexing the joints have been described earlier ( N j i and Wallee 1973). Action potentials were recorded extracellularly with flexible “suction electrodes” fitted into circular boreholes (Fig. 1). N o suction was needed, since the rubber coated electrode shaft stuck to the borehole after i t had been inserted as far as necessary to obtain good contact between electrode and nerve (branch of the second root innervating the extensor muscles). Situated close to the joint axis, the electrode-to-nerve contact was unaffected during the full range of movements in the joint. The amplifier activity was displayed on a cathode ray tube and photographed conventionally on moving film. Frequencies were counted over I s starting 0.5 s after the beginning of the step.
Fig. 1. Typical experimental arrangement. 3 simultaneous recordings are made from the right side of the second, third and fourth segments. Left: Zero reference position. Right: Selective flexion of the joint between the third and the fourth segments.
REFLEX INHIBITION OF STRETCH RECEPTORS
30
179
I-
." I
Imp/sec in s t r e t c h r e c e p t o r
Imp/sec in stretch receptor
Fig. 2. Reflex output from the large accessory neuron as a function of slowly adapting stretch receptor input. The stretch receptor o n the right side of the third segment was activated by pulling the receptor muscle with a fine glass hook (filled symbols) in between 2 series of fl-xion experiments (open symbols). Circlzs represent the reflex output i n the same segment and triangles the reflex output in the next anterior segment. Contralateral stretch receptors were denervated. Solid lines: First serizs of flexion experiments. Dashed lines: Second series of flexion experiments. and ipsilateral ( Q ) Fig. 3. Reflex output from the large accessory neuron E S a function of bilateral (0) slowly adapting stretch receptor input. The recording was made from the right side of the second segment during flexion. lpsilateral input was produced by denervation of the receptor on the opposite side. Two trials (solid and dashed lines) were performed in each situation.
In the experiments in which the reflex effects of pulling the receptor muscle were compared to those clicited by joint flexion, the dorsal part of the tergite of abdominal segments 2 , 3 and 4 were removed to expose the stretch receptors bilaterally. T he stretch receptors on the left side of these segments were denervated. The positions of the joints were controlled by means of pins inserted vertically through the animal on the left side, one in each segment from no. 2 through no. 5, instead of glass rods i n the midline.
Results Input-output relations of the large accessory reflex Impulse activity in a slowly adapting stretch receptor caused reflex activation of its own large accessory neuron. In addition, the large accessory neurons of several other abdominal segments were activated. Receptor activation by joint flexion produced the same reflex output as that produced by direct stretch of the receptor muscle strand, provided that the contralateral stretch receptor had been denervated. The results from one experiment are illustrated in Fig. 2, which shows the ipsilateral reflex outputs from the large accessory neurons in the same and neighbouring segments as a function of impulse frequency in the slowly adapting stretch receptor. There was no difference in the reflex output produced either by flexion or by direct mechanical activation of the receptor. 5 expts. on 4 animals all showed similar results. The effect of bilateral stretch receptor input was compared to that of unilateral input in several experiments. Ipsilateral input was obtained after cutting the nerve on the opposite side. Fig. 3 shows the results from a typical experiment. No difference occurred for most input frequencies. For input frequencies below about I5 imp/s, however, bilateral input was more effective than ipsilatera1 input.
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Fig. 4. Efficiency of the large accessory reflex couplings in the anterior and the oosterior directions. Data from 17 pairs of iarge accessory reflexes between neighbouring segments. The input frequency was 20 irnp/sec. A. The arrows represent the output frequencies in irnp/sec for the reflexes in the anterior (above the line) and the posterior (below the line) directions. B. Similar representation of the differences within pairs (anterior direction f posterior direction). Positive differences are shown above the line.
The distribution of this reflex to different abdominal segments is of obvious functional significance. Page and Sokolove (1972) recently published a report that emphasized the non-symmetrical distribution of the reflex. They found considerably stronger reflex connections from posterior to anterior segments than in the opposite direction and suggested that this could have important consequences in reflex function. We studied the symmetry of reflex coupling in 17 pairs of ipsilateral reflexes between neighbouring segments. In Fig. 4 A the reflex output (in imp/s) evoked by a stretch receptor input frequency of 20 imp/s is shown for each of the 34 reflexes. The difference between the output frequencies in the two directions appears to be small. The point estimate of the median of the output frequencies is 12 imp/s in the anterior direction and 9 imp/s in the posterior direction. The corresponding confidence intervals, with a confidence coefficient of 0.95, are 9 imp/s < q
