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Nozaki M, Bell JA, Vaupel DB, Martin WR. 
“Responses of the Flexor Reflex to LSD, Tryptamine, 5-Hydroxytryptophan, Methoxamine, and d-Amphetamine in Acute and Chronic Spinal Rats”. 
Psychopharmacology. 1977;55(1):13-18.
The effects of noradrenergic, tryptaminergic and serotonergic agonists and-an antagonist on the flexor reflex of acute and chronic spinal rats were studied. 277 Female Wistar rats (180-200g) had the T4-T6 spinal cord segment removed by suction under ether anesthesia. Acute ex - periments were carried out after 40-48 hr later in 130 rats (180-200g) and chronic experiments were carried out 2 mth after transection in the remainder (250-280g). d-Amphetamine (SK+F), methoxamine (Wellcome) LSD and 5-hydroxytryptophan (5-HTP, Calbiochem) were given i.p. at 0.5 ml/100 g, and tryptamine and L-tryptophan (both Sigma-Chem.) were given i.p. and i.v. at 1.0 ml/100 g, the effect on the hindfoot flexor reflex elicited by a tetanic stimulus given every 10 sec being recorded. Cyproheptadine (Merck-USA) at 0.4-5.0 mg/kg was used as antagonist. The stimulation necessary to evoke the same reflex was 36.90 +/- 2.54V in the acute and 13.64 +/- 0.87 V in the chronic spinal rat, Reflex amplitude in the acute rat was facilitated by i.p. amphetamine (2, 4 and 5 mg/kg), methoxamine (8.75 mg/kg) and LSD (1.25 and 4 mg/kg), while i.p. 0.875-4.375 mg/kg methoxamine, 2.5-100 mcg/kg LSD, 6 and 50 mg/kg tryptamine, 2.5-50 mg/kg 5-HTP, i.v. 150 and 300 mg/kg tryptophan failed to facilitate the reflex. However, i.v. 3.0 mg/kg tryptamine in acute spinal rats produced tonic extension of the hip and knee on which was superimposed knee flexion produced by the stimulus. The flexor reflex was depressed during tonic extension with low doses of tryptamine and following tonic extension after i.v. 6.0-25.0 mg/kg tryptamine. In chronic spinal rats i.p, 2 mg/kg amphetamine, 0.875 mg/kg methoxamina, 2.5 Mg/kg LSD, 6 mg/kg tryptamine and 3.75 mg/kg 5-HTP facilitated the reflex and also produced spontaneous movements. Tryptophan did not change the reflex in either acute or chronic spinal rats but it produced a facilitative trend in acute spinal rats. Cyproheptadine did not change refex amplitude itself but completely antagonized the facilitative effect of LSD and tryptamine in chronic rats, while failing to affect the result of 5-HTP administration. Conclusion The mode of action of LSD is similar to that of tryptamine but different to that of 5-HTP.
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