EFFECTS OF NEW s-TRIAZOLOBENZODIAZEPINE (D-4OTA) AND …

Japan. J. Pharmacol, 23, 83-96 (1973) 83

EFFECTS OF NEW s-TRIAZOLOBENZODIAZEPINE (D-4OTA)

AND OTHER CENTRAL MUSCLE RELAXANTS ON

SPINAL AND SUPRASPINAL REFLEXES IN CATS

Sukehiro CHIBA and Yuji NAGAWA Biological Research Laboratories, Central Research Division,

Takeda Chemical Industries, Ltd., Higashiyodogawa-ku, Osaka, Japan

Accepted 29 August 1972

Abstract-The inhibitory effect of benzodiazepine-type agents such as 8-chloro-6-

phenyl-4H-s-triazolo [4, 3a] [1, 4] benzodiazepine (D-40TA), diazepam and nitrazepam on the spinal and supraspinal polysynaptic reflexes was compared with that of mephene-sin, methocarbamol, chlorzoxazone and chlormezanone in cats. Benzodiazepines did not depress the spinal and supraspinal polysynaptic reflexes or reflex potentials in the spinal and the gallamine-immobilized cats. In these respects, chlormezanone resembled benzodiazepines. On the other hand, mephenesin, methocarbamol and chlorzoxazone blocked these reflexes in all kinds of preparations such as the anes-thetized, the spinal, the decerebrate and the gallamine-immobilized preparations. D-40TA depressed gamma rigidity at the dose below that necessary to depress alpha rigidity. Moreover, it inhibited more profoundly the tonic stretch reflex than the phasic one. Spontaneous and evoked discharges of the muscle spindle in the decerebrate cat were significantly depressed by D-40TA, while those of spinal cat were unaffected.These results suggest that skeletal muscle relaxation by benzodiazepines including D-40TA is attributed to the primary depression of the brain stem reticular system and in turn the ascending inhibitory action via the gamma system on the spinal and supraspinal polysynaptic neurons. It should be stressed that the integrity of the connection between the brain stem and gamma system in the spinal cord and its re-lated muscles is also required for eliciting the depression of supraspinal polysynaptic reflex by these agents. Mephenesin-type agents presumably inhibit directly the inter-neurons at the spinal and supraspinal levels.

Mephenesin, first introduced by Berger and Bradley (1) as the centrally acting muscle

relaxant, has been postulated to have a selective action on spinal interneuron as polysynap-

tic reflex responses were abolished without effect on monosynaptic reflex responses (2).

Later, the benzodiazepine agents have been found to possess tranquilizing and muscle

relaxant properties. The depression of polysynaptic spinal reflexes by diazepam, one

of these benzodiazepines, has been proposed to be due to the action principally on the

brain stem reticular formation, on the basis of the finding that spinal polysynaptic depres-

sion in decerebrate cats is nullified by spinal transection (3).

Our current study on the benzodiazepines led to the discovery of a new type of com-

pound, 8-chloro-6-phenyl-4H-s-triazolo [4, 3a] [1, 4]-benzodiazepine (D-40TA) which

was highly active in tranquilizing, sedative-hypnotic and muscle relaxant effects in experi-

mental animals (4). In our neuropharmacological study on this agent, the depression of

84 S. CHIBA & Y. NAGA WA

not only spinal polysynaptic reflex but also supraspinal polysynaptic reflex observed in

decerebrate cat was not demonstrated in spinal cat or in gallamine-immobilized cat. The

purpose of the present experiments was to clarify whether or not the mode of action of D-40TA is different from that of diazepam, nitrazepam, mephenesin and other central

muscle relaxants. The effect of D-40TA on the gamma system was also studied.

METHODS

Seventy-nine cats of both sexes weighing from 2.4 to 4.9 kg were used and the fol-lowing four kinds of preparations were made : Immobilized cat with gallamine triethiodide,

anesthetized cat with combination of a-chloralose (40 mg/kg, i.v.) and urethane (400 mg/

kg, i.p.), spinal cat with transection at Cl level and decerebrated cat at intercollicular level.

Immobilization with gallamine was preceded by ether anesthesia for surgical operation.

Transection of either the spinal cord or the brain stem was accomplished with a blunt

spatula under ether anesthesia. The gallamine-immobilized and the spinal cats were main-tained on artificial respiration. After surgical operation, the ether was withdrawn and

at least 3 hr elapsed before experimentation began. In gallamine-immobilized cats, the

pressure points were anesthetized with procaine.Experiments with mechanical responses of spinal and supraspinal reflexes were per-

formed in three kinds of preparations, the anesthetized, the spinal and the decerebrate cats.

After the head and bilateral femurs of animal were fixed on a stereotaxic instruments, the

patellar reflexes were elicited by tapping the right patellar tendon with an automatically operated magnetic hammer once every 5-10 sec. On the left hind limb, either flexor reflex response of the anterior tibialis muscle to supramaximal stimulation of the peroneal nerve

or ipsilateral extensor reflex response of the quadriceps femoris muscle to supramaximal

stimulation of the sciatic nerve were obtained. In some preparations, the left peroneal nerve was stimulated to provoke both flexor and contralateral extensor reflex responses.

The central cut end of either the peroneal or the sciatic nerve was placed on bipolar plati-

num stimulating electrodes. The parameters of stimuli, which were delivered from a

Nihon Koden electronic stimulator (MSE-3), were rectangular, 0.3 Hz in frequency and

5 msec in pulse duration. In addition to these spinal reflexes, supraspinal linguomandi-

bular reflex was also produced once per 3.3-5 sec by supramaximal stimulation of the ton-

gue through needle electrodes. These reflex responses were recorded by means of force-displacement transducers on a Nihon Koden polygraph (RM-150). At the same time,

the electromyogram (EMG) of extensor lateral digitorum muscle in forelimb and the bra-

chial arterial blood pressure were routinely recorded.

Experiments with electrical responses of spinal and supraspinal reflexes were per-

formed in the gallamine-immobilized cats and in the spinal or the decerebrate cats. After

the head, spine and ankle of animal were rigidly mounted on a stereotaxic instrument, the

animal was subjected to exposure of the lumbosacral cord and the popliteal fossa under

ether anesthesia. Following the surgical procedure, the exposed regions were covered

by liquid paraffin warmed at normal body temperature. All the ventral roots from L4

D-40TA ON SPINAL REFLEX 85

to Si were bilaterally severed in order to eliminate the feedback control through the gamma

loop. The central cut end of the tibial nerve was placed on the bipolar platinum stimulat-

ing electrodes. The stimulating pulses were rectangular, 0.3 Hz in frequency, 0.5 msec

in pulse duration and 4 times threshold for the spinal monosynaptic reflex potentials in

intensity. The spinal mono-and polysynaptic reflex potentials and dorsal root reflex

potentials were recorded by means of bipolar platinum recording electrodes attached to the central cut ends of L7 ventral root filaments and L6 dorsal root filaments, respectively.

For recording of supraspinal reflex potentials, the nerve innervating the digastric muscle

was exposed at the temporal fossa, and the central cut end of the lingual nerve was supra-

maximally stimulated. These reflex potentials were displayed on a Nihon Koden dual

beam oscilloscope (VC-7A) and photographed. In some decerebrate cats, only the ventral

and dorsal root filaments for recording and the tibial nerve for stimulation were severed

in order to observe the indirect effect on spinal reflex potentials through the gamma loop.

On the other hand, some other decerebrate cats were pretreated with gallamine to produce

functional deafferentation of muscle spindles.

Effects on phasic and tonic reflex responses were investigated, using decerebrate cats

according to the same method as that devised by Smith et al. (5). The Achilles tendon

was sectioned and attached to a force-displacement transducer mounted on an automatic

traction apparatus. The phasic stretch reflex was evoked by displacing the transducer

10 mm distally at a velocity of 100 mm/sec. Subsequently, by maintaining the displaced

state for 10 sec the tonic stretch reflex was evoked. The muscle tension caused by stretch

reflexes was determined by subtracting "passive" tension obtained after complete paralysis

induced by adequate dose of gallamine and nerve sectioning.

For the test of gamma rigidity of the decerebrated cats at intercollicular level, the

animals exhibiting marked rigidity were selected about 2 hr after the termination of ether

anesthesia. The resistance of shoulder, elbow, carpal, hip, knee and tarsal joints in four

limbs to forced flexor movement was scored from 0 for complete loss of resistance to 3

for severe rigidity before and after administration of the agent. Effects on alpha rigidity

of the decerebrated cats by ligating both the carotid and basilar arteries were also investi-

gated by recording of the EMGs of the biceps brachii muscle, triceps brachii muscle and trapezius muscle.

Effects on muscle spindle activity were observed in both the spinal and the decerebrate

cats. A single afferent fiber (G1a) originating from muscle spindle in the gastrocnemius

muscle was identified in the dorsal root filaments of L7 segment according to the criteria

of Hunt (6). The spontaneous and evoked spindle discharges caused by stretching the

muscle were recorded on the oscilloscope and photographed. For simultaneous record-

ing of the electrical activities of the alpha as well as gamma fibers, the decerebrate cats

were used. Filaments which showed sustained rhythmical discharges of relatively low

amplitude or impulses of comparatively high amplitude were selected from the severed

ventral root of L7 segment (7). With the exception of these ventral filaments for record-

ing and tibial nerve for stimulation, all the peripheral nerves of the hind limb tested and


the ventral and dorsal roots were left intact. The spontaneous gamma and reflexively evoked alpha and gamma efferent discharges by the tactile stimulation or the afferent stimulation

of the tibial nerve were displayed on dual beam oscilloscope and photographed.

D-40TA, nitrazepam and diazepam synthesized in this chemical laboratory were dis-

solved in 20 % glycofurol solution and mephenesin (MyoserolR, Sankyo) in 10 % pro-

pyleneglycol solution for injection into the radial vein. For intraperitoneal injection, chlorzoxazone (SolaxinR, Eisai), methocarbamol (RobaxinrR, Takeda) and chlormezanone

(TrancopalrR, Daiichi) were suspended in 5% gummi arabicum solution.

RESULTS

1) Effects on the patellar, flexor, ipsi-and contralateral extensor, linguomandibular re-

flexes and the EMG activity D-40TA showed a marked depressive effect on the flexor, ipsi- and contralateral ex-

tensor and linguomandibular reflexes in all of 5 decerebrate cats, as indicated in Fig. 1.

These effects reached a peak within 5 min after administration and lasted for 20 to 30 min

at the intravenous dose of 0.1 mg/kg, which was the minimum effective dose for inhibition

of the linguomandibular reflexes. The higher dose, 0.2 mg/kg, produced more than

FIG. 1. Effect of D-40TA on patellar reflex (PR), linguomandibular reflex (LMR) and ipsilateral extensor reflex (ER) in decerebrate cat.

BP.: blood pressure.

D-4OTA ON SPINAL REFLEX 87

80% depression in the flexor, ipsi-and contralateral extensor and linguomandibular re-

flexes for more than 2 hr. Increase in dosage levels of D-40TA caused longer depression

in duration. The EMG activity was also reduced for a long time, synchronized with the

depression of the spinal and linguomandibular reflexes. On the other hand, the change

in blood pressure induced by D-40TA was only a transient hypotension ranging from 20

to 40 mmHg, indicating no direct relationship between the fall of blood pressure and the

TABLE 1. Effects of various agents on linguomandibular (LMR), extensor (ER) and patellar (PR) reflexes in decerebrate cat.

↓: Depress, ↑: Augment, ―: Nochange .

FIG. 2. Effect of D-40TA on patellar reflex (PR), linguomandibular reflex (LMR) and ipsilateral extensor reflex (ER) in spinal cat.

BP.: blood pressure.


observed effects on these reflexes. The patellar reflexes were never depressed at the dosage

levels ranging from 0.2 to 2.0 mg/kg in the decerebrate preparations. Conversely, in some

animals, the seemingly diminished amplitude of the patellar reflexes caused by the increased

tonus of the quadriceps femoris muscle was enhanced to its normal amplitude by decreasing

the muscle tonus as the result of relieving decerebrate rigidity, the patellar reflexes being

normalized.

Comparative results obtained with D-40TA, nitrazepam, diazepam, methocarbamol,

chlormezanone, chlorzoxazone and mephenesin in the dosage levels capable of producing

more than 80 % depression in the contralateral extensor and linguomandibular reflexes of

3-5 decerebrate preparations are presented in Table 1.

On the other hand, the patellar, flexor, ipsi- and contralateral extensor and linguo-

mandibular reflexes in the spinal cats were not depressed by the intravenous injection of

0.2 to 2.0 mg/kg of D-40TA but rather augmented in 3 of 5 animals, as shown in Fig. 2.

Increase of dosage levels up to 10 mg/kg caused no modification. As shown in Table 2,

the data obtained using 3-5 spinal cats for each agent indicated that D-40TA resembled

nitrazepam, diazepam and chlormezanone, but differed from mephenesin, chlorzoxazone

and methocarbamol. All the latter three agents depressed the flexor, ispi- and contra-

lateral extensor and linguomandibular reflexes even in the spinal preparations.

In 4 ƒ¿-chloralose-urethanized cats, the intravenous dose of 0.125 mg/kg of D-40TA

depressed almost completely the flexor, ipsi-and contralateral extensor and linguoman-

dibular reflexes without affecting the patellar reflexes, for more or less than 4 hr. In con-

trast to the transient hypotension observed in the decerebrate and the spinal preparations,

a fall in blood pressure of the anesthetized preparations persisted during the depression

of the reflexes. The flexor and linguomandibular reflexes depressed by D-40TA were

restored to 70-80 % of control level after the spinal cord transection at Cl level. There-

after the restored reflexes were unchanged even after the additional dose of 2 to 10 mg/

kg of D-40TA, nitrazepam and diazepam, respectively, but clearly inhibited by the dose

of 25 mg/kg of mephenesin (Fig. 3).

TABLE 2. Effects of various agents on linguomandibular, extensor and patellar

reflexes in spinal cat.

↑ : Depress, ↓: Augment, ―: Nochange

D-4OTA ON SPINAL REFLEX 89

A) Anesthetized cat

B) 15 min after spinal section

2) Effects on the spinal and supraspinal reflex potentials

The spinal polysynaptic reflex potentials recorded from L7 ventral root of the de-

cerebrate cats, which maintained the gamma efferent and spindle afferent nerves intact

except the nerves for stimulation and recording, were reduced by more than 50 % follow-

ing the intravenous dose of 0.5 mg/kg of benzodiazepine-type agents such as D-40TA,

nitrazepam and diazepam, but the monosynaptic reflex potentials were unchanged or only

slightly augmented. At the same time, the dorsal root reflex potentials from L6 dorsal

root were augmented by about 200 %. (Fig. 4A). These effects persisted for more than

2 hr. On the other hand, polysynaptic reflex potentials in the preparations such as

the gallamine-immobilized and the spinal cats were never depressed even at the accumula-

tive dose of 2 mg/kg injected intravenously at 30 min intervals. The same results were

obtained in the decerebrate cats pretreated with gallamine. The dorsal root reflex po-

tentials, however, were maximally enhanced already at the intravenous dose of 0.2-0.5

mg/kg of these agents in all preparations. Fig. 5 shows comparative results of D-40TA

on the dorsal root reflex and mono-and polysynaptic reflex potentials in the gallamine-

immobilized, the spinal and the decerebrate cats.

Intravenous injection of 25 mg/kg of mephenesin, which is known to block the inter-

neurons at the spinal and reticular formation levels (8), considerably depressed the poly-

FIG. 3 A) Effect of D-40TA on linguomandibular reflex (LMR), flexor reflex (FR) and blood pressure (BP) in anesthetized cat. B) Effect of D-49TA and mephenesin on both reflexes after spinal transection.


A) Decerebrate cat

CONTROL

B) Gallamine-immobilized cat

FIG. 4 A) Effect of D-40TA on dorsal root reflex potentials (DRR) and spinal mono-and polysynaptic reflex potentials (SR) in decerebrate cat. B) Comparison of effects of D-40TA and mephenesin on DRR and spinal polysynaptic reflex potentials in gallamine-immobilized cat.

FIG. 5. Comparative results of D-40TA on dorsal root reflex potentials (DRR), spinal monosynaptic reflex potentials (DRR), spinal monosynaptic reflex poten-tials (MSR) and polysynaptic reflex potentials (PSR) in three kinds of prepa-rations, the gallamine-immobilized, the spinal and the decerebrate cats. Each point represents mean % change obtained from 5 animals.


A) Decerebrate cat

CONTROL

B) Galiamine-immobilized cat

FIG. 6. Effect of D-40TA on reflex potentials of the digastric nerve in response to afferent stimulation of the lingual nerve in decerebrate cat (A) and in gallamine-immobilized cat (B). Note failure of D-40TA to depress the reflex of gallamine-immobilized cat.

synaptic reflex potentials without augmenting the dorsal root reflex potentials in all pre-

parations such as the decerebrate, the spinal and the gallamine-immobilized cats. (Fig.

4B). In these respects, mephenesin resembled methocarbamol and chlorzoxazone.

Intravenous dose of 0.2 mg/kg of D-40TA also depressed the supraspinal polysynaptic

reflex potentials of the digastric nerve in response to afferent stimulation of the lingual

nerve in the decerebrate cats, as indicated in Fig. 6. Such a depressive effect of D-40TA,

however, was not observed in both the spinal and the gallamine-immobilized cats and

in the decerebrate cats pretreated with gallamine.

3) Effects on gamma and alpha rigidities and stretch reflexes

The inhibitory effect of D-40TA on the gamma driven rigidity was compared with

that of nitrazepam and diazepam, using the decerebrate cats exhibiting marked rigidity.

These agents at the intravenous dose of 0.5 mg/kg were applied at the hourly intervals.

The mean•}SEM. (mg/kg) of the dose which reduced the total score to 50 % of value ob-

tained before administration was 0.84•}0.09 (4 animals) for D-40TA, 2.27•}0.10 (4 animals)

for nitrazepam and 1.92•}0.55 (5 animals) for diazepam, respectively. D-40TA proved

to be twice as potent as nitrazepam and diazepam. The alpha rigidity induced by anemic

decerebration was unaffected by D-40TA at the intravenous dose of 1 mg/kg, but a sig-

nificant depression was observed following an intravenous dose above 3 mg/kg of D-40TA

in all of 3 preparations. These results indicate that the principal relaxant effect is on the

gamma rather than on the alpha motor system.

The effect of D-40TA on the stretch reflex caused by the afferent activity from muscle

spindle was investigated using 4 decerebrate cats. The abrupt stretching of the gastro-

cnemius muscle produced a rapidly developing reflexive contraction of the muscle (phasic

stretch reflex) only at the early period and the successively persistent reflexive contraction


(tonic stretch reflex) during maintained stretch. Maximum % depression (mean•}SEM.)

obtained after the intravenous injection of 0.5 mg/kg of D-40TA was 10.3•}5.9 for phasic

stretch reflex and 42.6•}4.4 for tonic stretch reflex. The depressing effect by this dose

lasted for about 4 hr.

4) Effects on gamma motor system

It was of interest to study the site of action of D-40TA in the gamma system. For

this purpose, the effects of D-40TA on the spontaneous and evoked spindle discharges

by stretching of the gastrocnemius muscle were observed in the decerebrate and the spinal

cats. As shown in Fig. 7, frequency of the spontaneous spindle discharges of Gla fiber

(conduction velocity, about 100 m/s) was 40 to 70 Hz and that of the discharges in response

to the muscle tension by stretching was 200 to 400 Hz. Intravenous injection of 0.5 mg/

kg of D-40TA depressed the spontaneous and evoked discharges of the muscle spindle

for more than 4 hr in all of 4 decerebrate cats, whereas, the spontaneous and evoked spindle

discharges of the same muscle in 3 spinal cats were not affected by D-40TA even at a high

dose of 2 mg/kg.

Further investigations were made by recording of the gamma efferent activity from

L7 ventral root of 3 decerebrate cats. Discharges of low amplitude occurring during a

slight stretching of the gastrocnemius muscle were regarded as originating from the efferent

activity of the gamma motoneurons. In addition to these gamma efferent discharges, the

spikes of high amplitude which were regarded as originating from the efferent activity

of the alpha motoneurons, were also evoked by tactile stimulation. As indicated in Fig.

8, D-40TA at an intravenous dose of 0.5 mg/kg depressed almost simultaneously both

the evoked discharges of high and low amplitudes. The reflexive alpha and gamma moto-

neur onal activities recorded from L7 ventral root in response to the afferent stimulation

CONTROL

10 min after D-40TA 0.5 mg/kg iv

FIG. 7. Effect of D-40TA on spontaneous and evoked spindle discharges recorded

from Gla fiber of L7 dorsal root in decerebrate cat.


a) spont.

b) tactile stim.

c) N. tibial stim.

of the tibial nerve were also depressed by the same treatment of D-40TA for more or less

than 4 hr.

DISCUSSION

The skeletal muscle relaxation by mephenesin-type agents such as methocarbamol

and chlorzoxazone is reported to be derived from the block of interneurons at the spinal

and supraspinal levels (9-12). In the present experiments, these agents blocked the spinal

polysynaptic reflexes, extensor and flexor reflexes, and the supraspinal polysynaptic re-flexes, linguomandibular reflex in three kinds of preparations such as the anesthetized,

the spinal and the decerebrate cats. Furthermore, the spinal polysynaptic reflex potentials

in the gallamine-immobilized, the spinal and the decerebrate cats were also reduced. These

results strongly suggest that mephenesin-type agents act on the interneurons at the spinal

and supraspinal levels. On the other hand, benzodiazepine-type agents did not depress

these reflexes and reflex potentials of the spinal and the gallamine-immobilized cats.

Ghelarducci et al. also reported no significant effect of nitrazepam on the spinal poly-

synaptic reflex potentials in the gallamine-immobilized, decerebrated cats (13). These

reflex responses and reflex potentials in the anesthetized and the decerebrate cats, which

are regarded as maintaining feedback control mechanism proposed by Hunt and Paintal

(14) and Eldred et al. (15), were however significantly inhibited by benzodiazepine-type

agents, In these respects, the action of chlormezanone was similar to benzodiazepine-

FIG. 8. Effect of D-40TA on spontaneous gamma motoneuronal discharges (a), and evoked alpha (high spike) and gamma (low spike) motoneuronal discharges

(b, c) recorded from alpha and gamma efferent fibers of L7 ventral root in decerebrate cat.


type agents.

It has been suggested that diazepam and nitrazepam augment presynaptic inhibition

in the spinal cord on the basis of the observation that the dorsal root reflex potentials were

remarkably augmented by these agents (16, 17). Eccles et al. (18) have postulated that

this increase in presynaptic inhibition gives rise to depression of the spinal polysynaptic

reflex potentials. Benzodiazepine-type agents, however, did not affect the spinal poly-

synaptic reflex potentials in the gallamine-immobilized and the spinal cats and in the de-

cerebrate cats pretreated with gallamine, although these agents augmented the reflex

potentials of the dorsal root. This augmenting effect, therefore, seems unlikely to be responsible for the depression of the spinal polysynaptic reflex potentials.

Ngai et al. (3) found that benzodiazepine-type agents are more active on the decereb-

rate than on the spinal cats concerning the skeletal muscle relaxing effect. It was also

reported that doses of benzodiazepine which did not affect the alpha motor system de-

pressed gamma rigidity (19). Many investigators have postulated that the mechanism of nitrazepam or diazepam producing skeletal muscle relaxation is due to an inhibitory

action on the brain stem reticular formation, most likely on the reticular facilitatory sys-

tem (13, 20, 21).

In the present experiments, marked inhibition of gamma rigidity was demonstrated

after the injection of nitrazepam, diazepam and D-40TA. Moreover, D-40TA depressed

gamma rigidity at the dose below that necessary to depress alpha rigidity. Also, D-40TA inhibited the tonic stretch reflexes of the gastrocnemius muscle, which is presumed to be

more dependent on the state of the gamma system than the phasic components (22). Such

high sensitivity of the gamma system to D-40TA in the decerebrate preparation implies

that the depression of the facilitatory control of the reticular formation is an important

factor for the manifestation of reduction of the polysynaptic reflexes by D-40TA. This

suggestion is supported by the reports (23-25) that the reticular formation has been de-monstrated to have a functionally close relation with the gamma system. However, the

possibility that the inhibitory effect on the reticular facilitatory system is a prerequisite for the depression of the polysynaptic reflexes is indicated by the following results obtained

in the present experiments.

The linguomandibular reflex responses of the spinal preparation were not depressed

by benzodiazepine-type agents but augmented in some instances. The depressed linguo-

mandibular reflexes by D-40TA in the anesthetized cat were restored to 70-80 % of control level after spinal transection at Cl level, and thereafter the restored reflexes were unaffected

even by the large doses of benzodiazepine-type agents. Furthermore, the reflex potentials

from the digastric nerve in response to the afferent stimulation of the lingual nerve in the functionally deafferented preparations such as the gallamine-immobilized cat or the de-

cerebrate cat pretreated with gallamine were also not modified by D-40TA. These

results suggest that the depression of the reticular facilitatory system by D-40TA affects

in turn an ascending influence via feedback control mechanism from the spinal cord and

its related muscle on supraspinal reflex pathway and results in the depression of the supra-


spinal polysynaptic reflexes. Such an interpretation is supported by the findings that

the digastric muscle seems to be devoid of muscle spindle (26), and that the controlling

and activating function of the gamma system on the alpha motoneuron is under inhibi-tory and facilitatory control of the reticular formation (27). For explanation of the

inhibition of the spinal polysynaptic reflexes, this interpretation is also favorable, since

benzodiazepine-type agents did not affect the reflexes in the preparation which lacked the feedback control mechanism by immobilizing the skeletal muscle with gallamine or

the supraspinal control by transecting the spinal cord at Cl level.

In the decerebrate cat, D-40TA caused a depression of the spontaneous and evoked

discharges of the G1a fiber derived from the muscle spindle, in contrast to no effect on

these discharges of the same fiber in the spinal preparation. Moreover, block of the

reflexive alpha motoneuronal activity appeared synchronously with that of the gamma

mononeuron. These results indicate that D-40TA depresses primarily the reticular for-

mation, affects in turn the gamma activity and thereby reduces the activity level of the

polysynaptic neurons. In conclusion, it is suggested that mephenesin-type agents inhibit interneurons at

the spinal and supraspinal levels to produce skeletal muscle relaxation. On the other

hand, the effect of benzodiazepine-type agents is attributed to an ascending inhibitory

action through the gamma system caused by the primary effect on the reticular formation.

Information gained from the present experiments suggest the clinical efficacy of D-

40TA for treatment of rigidity.

Acknowledgements: We are very grateful to Dr. K. Shimamoto for assistance with

the manuscript and to Mr. M. Funado for technical assistance.

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EFFECTS OF NEW s-TRIAZOLOBENZODIAZEPINE (D-4OTA) AND …