Nonspecific depressant action of γ-aminobutyric acid on somatic reflexes

The effects of γ-aminobutyric acid (GABA) on central integration of somatic reflexes in the cat have been studied by topical application, and by intrathecal or intracerebroventricular injection. Intrathecal injection of GABA inhibited the monosynaptic patellar reflex. The facilitation of the patellar reflex induced by strychnine, leptazol, tubocurarine and tetanus toxin was also inhibited. Polysynaptic facilitation of the patellar reflex induced in the spinal cat by electrical stimulation of the contralateral sciatic nerve was depressed by intrathecal GABA. Similarly, the supraspinal facilitation of the patellar reflex by electrical stimulation of the brain stem reticular formation was inhibited by application of GABA to the floor of the 4th ventricle. The polysynaptic inhibition of the patellar reflex at both levels was intensified by GABA. The flexor (tibialis anterior) reflex was depressed in the same manner as the extensor patellar reflex. The polysynaptic linguomandibular reflex was depressed by intracerebroventricular GABA. The depressant action of GABA at spinal and supraspinal levels of the neuraxis is discussed in relation to the role of GABA as an inhibitory transmitter in the central nervous system.