Motoneurone excitability after administration of a thyrotrophin releasing hormone analogue

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Abstract
1 Recordings have been made of motoneurone field potentials at vertebral level L1 to stimulation of the ventral root, in rats anaesthetized with urethane. 2 Injection of thyrotrophin releasing hormone (TRH) analogue RX77368 (2 mg kg−1) produced an increase in the amplitude of the field potential within 1 min of injection, reaching peak amplitude of 51–69% above control values 6–12 min after injection; the duration of the elevation was 30–65 min. 3 Arguments are presented which show that this effect is compatible with an RX77368-induced depolarization of the motoneurone, allowing the antidromic volley to invade more cell bodies.