Cortical pyramidal tract interneurones and their sensitivity to L‐glutamic acid

Abstract

SUMMARY1. Pyramidal tract interneurones, defined as neurones which are activated synaptically as a result of pyramidal tract stimulation, have been identified in the rat cerebral cortex. The number of evoked spikes depended upon stimulus strength, and stimulation in a specific thalamic nucleus produced a burst of activity lasting for up to 1 sec.2. These cells are readily excited by a brief (50 msec) pulse of glutamate applied by micro-iontophoresis. Other, unidentified cells are not so responsive.3. Synaptically evoked spikes resulting from pyramidal tract stimulation can be blocked by the iontophoretic and i.P. administration of substances shown to antagonize glutamate excitation of cells.4. The results support suggestions that glutamic acid is a neurotransmitter in the cerebral cortex. The evidence presented further indicates that glutamic acid could be the transmitter released by the pyramidal tract.

Amino Acids as Neurotransmitters of Corticofugal Neurones in the Rat: A Comparison of Glutamate and Aspartate

“…This supports previous studies which have indicated the possibility that an amino acid might be released as a neurotransmitter by corticofugal neurones entering the pyramidal tracts (Stone, 1973; or striatum (Spencer, 1976;Divac et al, 1977 ter is now sufficiently well documented to merit much fuller investigation both as regards its neurochemistry, and its pharmacology.…”

“…The characterization of units in the cerebral cortex which can be activated monosynaptically from the medullary pyramid has been described in a previous report (Stone, 1973). These units are primarily interneurones, though a small number of pyramidal tract neurones can themselves be excited synaptically.…”

“…On the basis of the marked sensitivity to L-glutamate shown by cortical neurones activated by the pyramidal tract, and the ability of antagonists of glutamate to block synaptically induced excitation, it was suggested that L-glutamate might be the excitatory neurotransmitter released by those corticofugal neurones forming the pyramidal tract (Stone, 1973;.…”

“…Extracellular recordings of unit activity were made with single glass microelectrodes containing 1 M potassium acetate and having resistances of 1 to 8 MQ at 1 kHz, fixed alongside the multibarrel pipettes (Stone, 1973 beyond the multibarrel tip.…”

Responses of Neurones in the Cerebral Cortex and Caudate Nucleus to Amantadine, Amphetamine and Dopamine

“…Unit activity was recorded through a single microelectrode containing molar potassium acetate or chloride, fixed alongside the iontophoretic complex (Stone, 1973b (1 ml/kg i.p.). A third group (4 rats) was treated 24 h before iontophoresis with a-methyl-p-tyrosine methyl ester hydrochloride (AMPT) (200 mg/kg i.p.)…”