[Effects of intra-arterially administered capsaicinoids on vocalization in guinea pigs and medial thalamic neuronal activity in cats (author's transl)].

Algesic actions of capsaicinoids were investigated by utilizing vocalization in conscious guinea pigs and medial thalamic neuronal activity in gallamine triethiodide immobilized cats. Intra-arterial administration of capsaicin and dihydrocapsaicin evoked strong vocalization response, but other capsaicinoids, nordihydrocapsaicin, homodihydrocapsaicin, homocapsaicin, norcapsaicin, N-(4-hydroxy-3-methoxybenzyl)-6-methylheptamide, and N-(4-hydroxy-3-methoxybenzyl)-6-methylhept-trans-4-enamide, were weaker than capsaicin and dihydrocapsaicin. Similar results were obtained from medial thalamic nociceptive neurons in cats. Morphine (10 mg/kg s.c.) suppressed vocalization response evoked by intra-arterial administration of capsaicin and bradykinin. Aspirin (100 mg/kg i.p.) also suppressed the bradykinin-evoked response, but not the capsaicin-evoked response. Capsi-amide, a non-pungent substance of Capsicum annuum L., failed to suppress nociceptive response to capsaicin or bradykinin in guinea pigs and cats. Tachyphylaxis was elicited by repeated administration of capsaicin in vocalization. No cross-tachyphylaxis to bradykinin, acetylcholine, and dihydrocapsaicin could be observed.