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The effect of diazepam on the spinal monosynaptic (H−) reflex in man
Neuropharmacology Pergamon
vol.
Press Ltd 1980.
19,
pp.
Printed
915 to 918 in Great Britain
PRELIMINARY NOTES
THE EFFECT OF OIAZEPAM
ON THE SPINAL MONOSYNAPTIC
(H-) REFLEX
IN MAN
John W. Crayton The University of Chicago Department of Psychiatry 950 East 59th Street Chicago, Illinois 60637
(Accepted
10 June 1980)
Summary - The effects of 10 and 20 mg oral doses of diazepam (OZ) on the excitability of a-motoneurons in man was assessed by measuring the recovery curve of the H-reflex in 12 subjects. DZ produced a statistically significant reduction in the peak of "secondary facilitation" (termed Hx) at both doses used. With the 10 mg dose, the maximal effects occurred at one hour, with a return toward baseline at 2 hours. Twenty mg DZ produced a greater effect which peaked at 2 hours. Individual differences in baseline H-reflex parameters and also in percent response to DZ were great. No significant effects on several other H-reflex parameters were found. The data are consistent with hypotheses suggesting that DZ acts primarily on supra-spinal mechanisms with descending influences on spinal motor neuron excitability. Diazepam (DZ) is a potent anti-anxiety, anti-seizure, and muscle-relaxing medication. Despite great interest in this drug, its mechanism of action remains to be elucidated. Studies have suggested that it acts at numerous sites in the nervous system such as the (Tallman et cortex, the reticular formation, peripheral nerves, and directly on muscle. al. 1980.) This study focuses on the effect of diazepam on the excitability synaptic reflex as demonstrated by H-reflex testing.
MATERIALS
of the spinal mono-
AND METHODS
Subjects Ten normal, healthy volunteers participated in the study; 5 were female and 5 were male. All subjects received physical examinations prior to the study and were asked to complete a medical questionnaire that included items concerning any history of significant neurological or emotional disease, and medication history. Volunteers with positive histories were excluded from the study. Written informed consent was obtained from all subjects. Drug Administration Diazepam tablets (Valium-Roche) were administered in 10 and 20 milligram doses following a baseline determination of spinal reflex (H-reflex) excitability parameters. Subjects were studied after 1 and 2 hours. Eight subjects were tested at both 10 and 20 mgs., 2 subjects were studied only with the 10 mg. dosage. H-reflex
Testing
The method for eliciting the spinal monosynaptic reflex was described in detail by Hugon (1973). In our study, the subjects semi-reclined in a large easy chair, with the legs extended at about 30 degrees of flexion and fixed by a tubular support system. A bipolar stimulating electrode (Beckman) was placed in the popliteal fossa over the posterior tibia1 nerve to elicit an optimal reflex response. Other details of recording are as described previously. (Crayton and King, 1980) The delay between the stimulus pairs ranged from 50 to 5000 msecs. Stimulus pairs were separated by 8 seconds. H2 (the amplitude of the response to the second of the paired stimuli 915
916
Preliminary Notes
was expressed as a percentage of Hl (the response of the first stimulus). All plots express the mean 2 S.E.M. of 5 determinations. RESULTS H-reflex There were no statistically significant changes in H-latency, the time from stimulation to H-reflex response; H-maximum, the maximum amplitude (mV) of the H-reflex; Mmaximum, the maximum elicitable M response; or H-max/M-max (Kruksal-Wallisone-Way ANOVA). Recovery Cycle Recovery curve changes were assessed by measuring Ho, the delay time at the onset of recovery, Hx, the peak of "secondary facilitation" occurring between 100-300 msec. delay, and H the value for HZ/H1 at the bottom of the following trough. The uniform effect of DZ was tg reduce the extent of recovery at various delays (Table I). Paired t-tests (Direct-DifferenceMethod) yielded statistically significant decreases in H, (p. ~0.05) at both doses and both times studied. Diazepam produced reductions in the curves and prolongaTable I Dose/Time
Ho (msec)
H,
(%I
Hy
(%I
Baseline
61.3 + 15.4
74.4 + 26.8
One Hour
85.0 + 46.9
63.6 + 22.7*
57.8 ? 17.5 53.8 + 20.4(5)
Two Hours
82.5 + 31.1
63.1 + 22.3*
65.4 + 14.8
Baseline
54.0 + 14.3
85.6 + 21.8
67.2 + 14.7(9)
One Hour
82.0 + 44.0
68.2 + 25.4*
61.0 + 17.5(6)
Two Hours
90.0 + 42.7
58.0 ? 17.3** 53.8 + 19.5(6)
Table I -- Group mean data ? SD for H-reflex recovery parameters Ho, H,, and H for 10 and 20 mg diazepam. "P < Numbers in parentheses indicate number of subjects' data used in calculation. For means without parentheses, N=8 for DZ 10 mg study; N=lO for DZ 20 mg study. Because of altered curve configurations, Hy could not be measured for all subjects. tion of initial recovery, as indicated by the changes in Ho, H,, and Hy. This effect is illustrated in the plots of the group mean recovery cycle at 1 and 2 hours post-drug at 10 and 20 mg doses in Fig. 1 A-B. This figure further illustrates that the largest effect of diazepam is on the curve values for delays between 100 and 300 msec. A smaller curvelowering effect is seen at delays between 800 and 2000 msec. In order to determine whether the change in H, with DZ was a function of the baseline value of H,, we sought correlations between baseline H, and change in H, with 10 and 20 mg at 1 and 2 hours. With 10 mg there was a tendency for the greatest drop in H, to occur at intermediate (70-90%) baseline values of H,. At 20 mg a similar pattern was seen, however, 2 additional subjects who had baseline H, values (102% and 125%), demonstrated the largest responses in the group. Subjects were asked for their impressions of the major effects of the drug on their level of arousal and alertness. In 7 of 10 subjects, the time of greatest change in Hx correlated with a subjective rating of maximal drug effect for the 20 mg dose. One subject felt no effects, and 2 described the greatest effect at 1 hour, although their H, showed a greater change at 2 hours. Since only minimal changes were noted in Ho, Hy, and other H-reflex parameters, no correlations with time course of effect between alertness-arousal and these measures could be determined. Time Course of the Effect The time course of the response to the drug shows 2 patterns. In some cases, particularly at 20 mg, DZ produced a progressive depression of the recovery curve, as seen in our results at 1 and 2 hours after administration. With the smaller dose, 10 mg of DZ, one could see a partial return of the curve toward normal and toward the pre-drug level at 2 hours.
Preliminary Notes
IOO-
917
IOmg VALIUM
60 -
2
60-
T I”
40-
0-
Barin*
-
I Hour
&---
2 Ham
l
20 -
f 50
1 100
I 500
I 200 S,
I tOO0
I 2000
1 5000
S, Delayimsec)
A 2Omg VALIUM
80
I 50
I
I 100
200 SlS2
Figure 1.
I
I
500
Iooo
I 2000
I 5000
Delay(msec)
Effects of DZ on the H-reflex recovery curve at 1 and 2 hours. Group mean values for (A) 10 mg, (8) 20 mg. Vertical bars indicate S.E.M. DISCUSSION
Diazepam produces 2 principal effects on the H-reflex recovery curve: (1) to shift the excitability curve toward the right, i.e., to delay recovery; and (2) to reduce the extent of recovery during the phase of secondary facilitation. The most prominent effect of DZ was to reduce the peak of secondary facilitation (H,). The origin of this peak has been the subject of considerable interest. Taborikova and Sax (1968) as well as Gassel (1970) have suggested that the peak is the result of long-loop reflexes which exert a facilitatory influence on spinal cord mechanisms. The possibility that.part of the secondary facilitation is due to intrinsic spinal cord mechanisms has also been supported by Gassel (19701 and Masland (1972). An effect of DZ on descending brain stem pathways has Geen suggested by its effect on vibration-inducedfnhibition of the H-reflex in intact and spinal cord-transected patients. Patients with transections fail to show au~nted inhibition in response to DZ, whereas intact subjects have a pronounced au~ntation effect (Yerrfer et al. 1975). N P 19/9 --”
918
Preliminary Notes
Taken together these studies suggest 2 hypotheses; that diazepam acts either through brain stem mechanfsm to alter the configuration of the H-reflex recovery curve, or directly on presynaptic inhibftory circuits in the spfnal cord. The evidence reviewed suggests that, in intact subjects, brain stem mechanisms can enhance the effect of DZ on presynaptic inhibition. Other mechanisms must also be considered however. Benzodiazepines have been shown to interact with other neurdtransmitter receptors in the brain, such as glycine receptors, and on dopaminergic and serotoninergic neurons. (Tallman et al. 1980) Further studies of the effects of benzodiazepines and other centrally acting substances will help to elucidate further the basis for H-reflex excitability and clarify the mode of action of these drugs. ACKNOWLEDGMENTS The technical assistance of Sheila King and Joel Finkel, statistical analysis of Richard Rued, and manuscript preparation by Dorothy Howard are gratefully acknowledged. Supported by USPHS Research Scientist Development Award MH 28151 and PHS Grant MH 27581. REFERENCES Crayton, J.W. and King, S. (1980) Inter-individualvariability of the H-reflex. Electromyography and Clinical Neurophysiology, in press. Gassel, M. (1970). A critical review of evidence concerning long-loop reflexes excited by muscle afferents in man. J. Neural., Neurosurg., and Psychiat. 33:350-362. Hugon, M. (1973). Methodology of the Hoffman reflex in man. In: NewTievelo rnentsin -*Electromyographyand Clinical Neurophysiology (Desmedt, J., Ed. Bal Facilitation during the H-reflex recovery curve. Arch. Neurol. Masla$rg~'(19~~): 26:313-319. Tabor%ova, H. and Sax, D. (1968). Motorneuron pool and the H-reflex. J. Neurol. Psychiat. 31:354-361. Tallman, J.F., %.11, S.M., Skolnick, P., and Gallager, D.W. (1980). Receptors for the age of anxiety: pharmacology of the benzodiazepines. Science 207:274-281. Verrier, M., MacLeod, S., Ashby, P. (1975). The effect of diaze=on presynaptic inhibition in patients with complete and incomplete spinal cord lesions. Le Journal Canadien des Sciences Neurolog. Aug. 179-184.
vol.
Press Ltd 1980.
19,
pp.
Printed
915 to 918 in Great Britain
PRELIMINARY NOTES
THE EFFECT OF OIAZEPAM
ON THE SPINAL MONOSYNAPTIC
(H-) REFLEX
IN MAN
John W. Crayton The University of Chicago Department of Psychiatry 950 East 59th Street Chicago, Illinois 60637
(Accepted
10 June 1980)
Summary - The effects of 10 and 20 mg oral doses of diazepam (OZ) on the excitability of a-motoneurons in man was assessed by measuring the recovery curve of the H-reflex in 12 subjects. DZ produced a statistically significant reduction in the peak of "secondary facilitation" (termed Hx) at both doses used. With the 10 mg dose, the maximal effects occurred at one hour, with a return toward baseline at 2 hours. Twenty mg DZ produced a greater effect which peaked at 2 hours. Individual differences in baseline H-reflex parameters and also in percent response to DZ were great. No significant effects on several other H-reflex parameters were found. The data are consistent with hypotheses suggesting that DZ acts primarily on supra-spinal mechanisms with descending influences on spinal motor neuron excitability. Diazepam (DZ) is a potent anti-anxiety, anti-seizure, and muscle-relaxing medication. Despite great interest in this drug, its mechanism of action remains to be elucidated. Studies have suggested that it acts at numerous sites in the nervous system such as the (Tallman et cortex, the reticular formation, peripheral nerves, and directly on muscle. al. 1980.) This study focuses on the effect of diazepam on the excitability synaptic reflex as demonstrated by H-reflex testing.
MATERIALS
of the spinal mono-
AND METHODS
Subjects Ten normal, healthy volunteers participated in the study; 5 were female and 5 were male. All subjects received physical examinations prior to the study and were asked to complete a medical questionnaire that included items concerning any history of significant neurological or emotional disease, and medication history. Volunteers with positive histories were excluded from the study. Written informed consent was obtained from all subjects. Drug Administration Diazepam tablets (Valium-Roche) were administered in 10 and 20 milligram doses following a baseline determination of spinal reflex (H-reflex) excitability parameters. Subjects were studied after 1 and 2 hours. Eight subjects were tested at both 10 and 20 mgs., 2 subjects were studied only with the 10 mg. dosage. H-reflex
Testing
The method for eliciting the spinal monosynaptic reflex was described in detail by Hugon (1973). In our study, the subjects semi-reclined in a large easy chair, with the legs extended at about 30 degrees of flexion and fixed by a tubular support system. A bipolar stimulating electrode (Beckman) was placed in the popliteal fossa over the posterior tibia1 nerve to elicit an optimal reflex response. Other details of recording are as described previously. (Crayton and King, 1980) The delay between the stimulus pairs ranged from 50 to 5000 msecs. Stimulus pairs were separated by 8 seconds. H2 (the amplitude of the response to the second of the paired stimuli 915
916
Preliminary Notes
was expressed as a percentage of Hl (the response of the first stimulus). All plots express the mean 2 S.E.M. of 5 determinations. RESULTS H-reflex There were no statistically significant changes in H-latency, the time from stimulation to H-reflex response; H-maximum, the maximum amplitude (mV) of the H-reflex; Mmaximum, the maximum elicitable M response; or H-max/M-max (Kruksal-Wallisone-Way ANOVA). Recovery Cycle Recovery curve changes were assessed by measuring Ho, the delay time at the onset of recovery, Hx, the peak of "secondary facilitation" occurring between 100-300 msec. delay, and H the value for HZ/H1 at the bottom of the following trough. The uniform effect of DZ was tg reduce the extent of recovery at various delays (Table I). Paired t-tests (Direct-DifferenceMethod) yielded statistically significant decreases in H, (p. ~0.05) at both doses and both times studied. Diazepam produced reductions in the curves and prolongaTable I Dose/Time
Ho (msec)
H,
(%I
Hy
(%I
Baseline
61.3 + 15.4
74.4 + 26.8
One Hour
85.0 + 46.9
63.6 + 22.7*
57.8 ? 17.5 53.8 + 20.4(5)
Two Hours
82.5 + 31.1
63.1 + 22.3*
65.4 + 14.8
Baseline
54.0 + 14.3
85.6 + 21.8
67.2 + 14.7(9)
One Hour
82.0 + 44.0
68.2 + 25.4*
61.0 + 17.5(6)
Two Hours
90.0 + 42.7
58.0 ? 17.3** 53.8 + 19.5(6)
Table I -- Group mean data ? SD for H-reflex recovery parameters Ho, H,, and H for 10 and 20 mg diazepam. "P < Numbers in parentheses indicate number of subjects' data used in calculation. For means without parentheses, N=8 for DZ 10 mg study; N=lO for DZ 20 mg study. Because of altered curve configurations, Hy could not be measured for all subjects. tion of initial recovery, as indicated by the changes in Ho, H,, and Hy. This effect is illustrated in the plots of the group mean recovery cycle at 1 and 2 hours post-drug at 10 and 20 mg doses in Fig. 1 A-B. This figure further illustrates that the largest effect of diazepam is on the curve values for delays between 100 and 300 msec. A smaller curvelowering effect is seen at delays between 800 and 2000 msec. In order to determine whether the change in H, with DZ was a function of the baseline value of H,, we sought correlations between baseline H, and change in H, with 10 and 20 mg at 1 and 2 hours. With 10 mg there was a tendency for the greatest drop in H, to occur at intermediate (70-90%) baseline values of H,. At 20 mg a similar pattern was seen, however, 2 additional subjects who had baseline H, values (102% and 125%), demonstrated the largest responses in the group. Subjects were asked for their impressions of the major effects of the drug on their level of arousal and alertness. In 7 of 10 subjects, the time of greatest change in Hx correlated with a subjective rating of maximal drug effect for the 20 mg dose. One subject felt no effects, and 2 described the greatest effect at 1 hour, although their H, showed a greater change at 2 hours. Since only minimal changes were noted in Ho, Hy, and other H-reflex parameters, no correlations with time course of effect between alertness-arousal and these measures could be determined. Time Course of the Effect The time course of the response to the drug shows 2 patterns. In some cases, particularly at 20 mg, DZ produced a progressive depression of the recovery curve, as seen in our results at 1 and 2 hours after administration. With the smaller dose, 10 mg of DZ, one could see a partial return of the curve toward normal and toward the pre-drug level at 2 hours.
Preliminary Notes
IOO-
917
IOmg VALIUM
60 -
2
60-
T I”
40-
0-
Barin*
-
I Hour
&---
2 Ham
l
20 -
f 50
1 100
I 500
I 200 S,
I tOO0
I 2000
1 5000
S, Delayimsec)
A 2Omg VALIUM
80
I 50
I
I 100
200 SlS2
Figure 1.
I
I
500
Iooo
I 2000
I 5000
Delay(msec)
Effects of DZ on the H-reflex recovery curve at 1 and 2 hours. Group mean values for (A) 10 mg, (8) 20 mg. Vertical bars indicate S.E.M. DISCUSSION
Diazepam produces 2 principal effects on the H-reflex recovery curve: (1) to shift the excitability curve toward the right, i.e., to delay recovery; and (2) to reduce the extent of recovery during the phase of secondary facilitation. The most prominent effect of DZ was to reduce the peak of secondary facilitation (H,). The origin of this peak has been the subject of considerable interest. Taborikova and Sax (1968) as well as Gassel (1970) have suggested that the peak is the result of long-loop reflexes which exert a facilitatory influence on spinal cord mechanisms. The possibility that.part of the secondary facilitation is due to intrinsic spinal cord mechanisms has also been supported by Gassel (19701 and Masland (1972). An effect of DZ on descending brain stem pathways has Geen suggested by its effect on vibration-inducedfnhibition of the H-reflex in intact and spinal cord-transected patients. Patients with transections fail to show au~nted inhibition in response to DZ, whereas intact subjects have a pronounced au~ntation effect (Yerrfer et al. 1975). N P 19/9 --”
918
Preliminary Notes
Taken together these studies suggest 2 hypotheses; that diazepam acts either through brain stem mechanfsm to alter the configuration of the H-reflex recovery curve, or directly on presynaptic inhibftory circuits in the spfnal cord. The evidence reviewed suggests that, in intact subjects, brain stem mechanisms can enhance the effect of DZ on presynaptic inhibition. Other mechanisms must also be considered however. Benzodiazepines have been shown to interact with other neurdtransmitter receptors in the brain, such as glycine receptors, and on dopaminergic and serotoninergic neurons. (Tallman et al. 1980) Further studies of the effects of benzodiazepines and other centrally acting substances will help to elucidate further the basis for H-reflex excitability and clarify the mode of action of these drugs. ACKNOWLEDGMENTS The technical assistance of Sheila King and Joel Finkel, statistical analysis of Richard Rued, and manuscript preparation by Dorothy Howard are gratefully acknowledged. Supported by USPHS Research Scientist Development Award MH 28151 and PHS Grant MH 27581. REFERENCES Crayton, J.W. and King, S. (1980) Inter-individualvariability of the H-reflex. Electromyography and Clinical Neurophysiology, in press. Gassel, M. (1970). A critical review of evidence concerning long-loop reflexes excited by muscle afferents in man. J. Neural., Neurosurg., and Psychiat. 33:350-362. Hugon, M. (1973). Methodology of the Hoffman reflex in man. In: NewTievelo rnentsin -*Electromyographyand Clinical Neurophysiology (Desmedt, J., Ed. Bal Facilitation during the H-reflex recovery curve. Arch. Neurol. Masla$rg~'(19~~): 26:313-319. Tabor%ova, H. and Sax, D. (1968). Motorneuron pool and the H-reflex. J. Neurol. Psychiat. 31:354-361. Tallman, J.F., %.11, S.M., Skolnick, P., and Gallager, D.W. (1980). Receptors for the age of anxiety: pharmacology of the benzodiazepines. Science 207:274-281. Verrier, M., MacLeod, S., Ashby, P. (1975). The effect of diaze=on presynaptic inhibition in patients with complete and incomplete spinal cord lesions. Le Journal Canadien des Sciences Neurolog. Aug. 179-184.