On the pharmacology of ascending, descending and recurrent postsynatic inhibition of the cuneo‐thalamic relay cells in the cat

Abstract

Summary1. In cats decerebrated or anaesthetized with pentobarbitone, cells of the middle third of the cuneate nucleus that were excited by tactile stimulation of the ipsilateral forelimb (responding to displacement of hairs, skin or joints) and inhibited by electrical stimulation of the contralateral pyramid, were invariably inhibited by electrical stimulation of the ipsilateral forepaw and the contralateral forelimb nerves. 2. In 50% of the cats, the cells were more fully identified by placing electrodes stereotaxically in the contralateral medial lemniscus. Recurrent inhibition was always a concomitant of the antidromic action potential. 3. The intensity and the duration of inhibition evoked by all of these pathways was totally resistant to iontophoretic and intravenous strychnine in doses at least 5 times that required to block completely the response of the same cells to iontophoretic glycine and was extremely sensitive to either iontophoretic bicuculline or picrotoxin. 4. Although the inhibition was invariably sensitive to intravenous picrotoxin, no significant change occurred in the duration or intensity of the inhibition when bicuculline was administered intravenously (5 or 6 times) as repeated doses of 0-2 mg/kg. 5. Postsynaptic inhibition in the cuneate may be mediated by y-aminobutyric acid released from the nerve terminals of a common pool of interneurones shared by ascending, descending and recurrent pathways. Since the receptors involved in this pathway are resistant to intravenous bicuculline, they may well be distinct from those responsible for changes in the primary afferent terminal excitability, usually believed to be associated with presynaptic inhibition.

Processing Afferent Proprioceptive Information at the Main Cuneate Nucleus of Anesthetized Cats

“…8 A, Control). This presumed recurrent suppression (Kelly and Renaud, 1973;Canedo et al, 2000) was observed at stimulating frequencies of up to 20 -25 Hz and was canceled by application of BiCu (Fig. 8 A, right) and/or strychnine.…”

Antagonism of Γ‐aminobutyric Acid and Glycine by Convulsants in the Cuneate Nucleus of Cat

“…An alternative explanation could involve the possibly different distributions of GABA receptors at pre-and post-synaptic sites in cuneate nucleus and cerebral cortex. Both pre-and post-synaptic inhibition have been demonstrated in the cuneate nucleus (Andersen, Etholm & Gordon, 1970) and GABA has been suggested as the transmitter for both mechanisms (Banna & Jabbur, 1969;Davidson & Reisine, 1971;Kelly & Renaud, 1971;Banna, Naccache & Jabbur, 1972;Kelly & Renaud, 1973c). In the cortex, however, only a post-synaptic action of GABA has been shown to occur, as yet (Krnjevic & Schwartz, 1968).…”

On the pharmacology of the γ‐aminobutyric acid receptors on the cuneo‐thalamic relay cells of the cat

“…Similar degrees of block occurred whether the cells were excited postsynaptically by glutamate or transynaptically by peripheral stimulation of hair, touch or joint cells. In the second paper (Kelly & Renaud, 1973a) glycine is shown to be selectively blocked by extremely small and short iontophoretic applications of strychnine. The third paper (Kelly & Renaud, 1973b) describes the influence of bicuculline, picrotoxin and strychnine on the duration and intensity of inhibition of cuneothalamic relay cells.…”