Evidence for involvement of α2Adreonceptors in the nucleus ambiguus in baroreflex-mediated bradycardia

  • S. Gurtu
  • D. K. Sharma
  • J. N. Sinha
  • K. P. Bhargava


Microinjection of noradrenaline and clonidine into the nucleus ambiguus elicited dose-dependent bradycardia with insignificant alteration of blood pressure. Phenylephrine failed to elicit any cardiovascular effect. The bradycardic effects of noradrenaline and clonidine were antagonized by piperoxan but not by phenoxybenzamine. Adrenergic neurone blockade with local guanethidine pretreatment also abolished the response to clonidine. No significant cardiovascular effect of clonidine microinjection into the nucleus ambiguus was observed in bilaterally vagotomized animals. The baroreflex bradycardia induced by volume loading was abolished by yohimbine and piperoxan by volume loading was abolished by yohimbine and piperoxan but not by phenoxybenzamine, microinjected bilaterally into the nucleus ambiguus. These results demonstrate the presence of cardioinhihibitory, presynaptic α2-adrenoceptors in the nucleus ambiguus and their involvement in baroreflex bradycardia.

Key words

Baroreflex α2-Adrenoceptors Nucleus ambiguus Clonidme Noradrenaline 


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Anderson FD, Berry CM (1956) An oscillographic study of the central pathways of the vagus nerve in the cat. J Comp Neurol 1106:161–181Google Scholar
  2. Antonaccio MJ (1977) Neuropharmacology of central mechanisms governing the circulation. In: Antonaccio MJ (ed) Cardiovascular pharmacology. Raven Press, New York, pp 131–165Google Scholar
  3. Bhargava KP, Misra N, Tangri KK (1972) An analysis of central adrenoceptors for control of cardiovascular functions. Br J Pharmacol 45:596–602Google Scholar
  4. Bhargava KP, Jain IP, Saxena AK, Sinha JN, Tangri KK (1978) Central adrenoceptors and cholinoceptors in cardiovascular control. Br J Pharmacol 63:7–15Google Scholar
  5. Calaresu FR, Cottle MK (1965) Origin of cardiomotor fibres in the dorsal nucleus of the vagus in the cat. A histological study. J Physiol (Lond) 176:252–260Google Scholar
  6. Chiba T, Kato M (1978) Synaptic structure and qualification of catecholaminergic axons in the nucleus tractus solitarius of the rat. Possible modulatory roles of catecholamines in baroreceptor reflexes. Br Res 151:323–338Google Scholar
  7. Ciriello J, Calaresu FR (1980) Distribution of vagal cadioinhibitory neurones in the medulla of the cat. Am J Physiol 238:R57-R58Google Scholar
  8. Cottle MK (1964) Degeneration studies of primary afferents of IXth and Xth cranial nerves in the cat. J Comp Neurol 161:143–158Google Scholar
  9. Day MD, Poyser RH, Sempik J (1980) Effects on blood pressure of noradrenaline and isoprenaline administered into the third ventricle of the brain of anaesthetized and conscious cats. J Auton Pharmacol 1:27–43Google Scholar
  10. De Jong W (1974) Noradrenaline: Central inhibitory control of blood pressure and heart rate. Eur J Pharmacol 29:179–181Google Scholar
  11. Fuxe K, Hökfelt T, Goldstein N, Jonsson G, Lindbrink P, Ljung Dahl A, Sachs CH (1975) Topography of central catechlamine pathways: Symposium on central action of drugs in the regulation of blood pressure. Royal Post-graduate Medical School, LondonGoogle Scholar
  12. Gunn CG, Sevelius G, Puiggari MJ, Myers FK (1968) Vagal cardiomotor mechanisms in the hind brain of the dog and cat. Am J Physiol 214:258–262Google Scholar
  13. Gurtu S, Sinha JN, Bhargava KP (1982) Involvement of α2-adrenoceptors of nucleus tractus solitarius in baroreflex mediated bradycardia. Naunyn-Schmiedeberg's Arch Pharmacol 321:38–43Google Scholar
  14. Haeusler G (1975) Cardiovascular regulation of central adrenergic mechanisms and its alteration by hypotensive drugs. Circ Res 36 and 37, Suppl 1:223–232Google Scholar
  15. Hökfelt T, Fuxe K, Goldstein M, Johansson D (1974) Immunochemical evidence for the existence of adrenaline neurones in rat brain. Br Res 66:232–251Google Scholar
  16. Kerr FWL (1962) Facial, vagal and glossopharyngeal nerves in the cat: afferent connections. Arch Neurol (Chic) 6:264–281Google Scholar
  17. Kerr FWL (1969) Preserved vagal viscerometer functions following destruction of the dorsal motor nucleus. J Physiol (Lond) 203:755–769Google Scholar
  18. Kobinger W, Walland A (1971) Involvement of adrenergic receptors in central vagus activity. Eur J Pharmacol 16:120–122Google Scholar
  19. Kobinger W, Walland A (1972a) Evidence for a central activation of a vagal cardiodepressor reflex by clonidine. Eur J Pharmacol 19:203–209Google Scholar
  20. Kobinger W, Walland A (1972b) Facilitation of vagal reflex bradycardia by an action of clonidine on central receptors. Eur J Pharmacol 19:210–217Google Scholar
  21. Kubo T, Misu Y (1981) Pharmacological characterization of the α-adrenoceptors responsible for a decrease of blood pressure in the nucleus tractus solitarius of the rat. Naunyn-Schmiedeberg's Arch Pharmacol 317:120–125Google Scholar
  22. Langer SZ (1978) Modern concepts of adrenergic transmission. In: Legg NI (ed) Neurotransmitter systems and their clinical disorders. Academic Press, New York, pp 29–51Google Scholar
  23. Langer SZ (1980) Presynaptic regulation of the release of catecholamines. Pharmacol Rev 32:337–362Google Scholar
  24. Loizou LA (1969) Projections of the nucleus locus coeruleus in the albino rat. Br. Res 15:536–566Google Scholar
  25. Mitchell G, Warwick R (1955) The dorsal vagal nucleus. Acta Anat 25:371–395Google Scholar
  26. Philippu A, Schartner P (1976) Inhibition by locally applied alpha-adrenoceptor blocking drugs of the depressor response to stimulation of the anterior hypothalamus. Naunyn-Schmiedeberg's Arch Pharmacol 295:1–7Google Scholar
  27. Rhoton AL Jr, O'leary JL, Ferguson JP (1966) Trigeminal, facial, vagal and glossopharyngeal nerves in the monkey. Arch Neurol Psychiat 14:530–540Google Scholar
  28. Schmitt H, Fenard S (1971) Effects des substances α-sympathomimetiques sur les centres vasomoteurs apre's administration intraveinneuse on intraventriculaire. Arch Int Pharmacodyn 190:229–240Google Scholar
  29. Sinha JN, Tangri KK, Bhargava KP, Schmitt H (1975) Central sites of sympatho-inhibitory effects of clonidine and l-dopa. International Symposium on Hypertension. Monte-Carlo, Monaco. Proc. In: Milliez P, Safar M (eds) Recent advances in hypertension, vol I. Boehringer-Ingelheim, Reims, pp 97–109Google Scholar
  30. Sinha JN, Gurtu S, Bhargava KP (1981) Effect of microinjection of α-adrenoceptor agonists and antagonist into medullary cardioinhibitory loci: Abs 374, Proceedings of the VIII International Conference of IUPHAR. Tokyo, JapanGoogle Scholar
  31. Snider RS, Niemer WT (1961) A stereotaxic atlas of the cat brain. The University of Chicago PressGoogle Scholar
  32. Starke K, Montel H, Gayk, W, Merker R (1974) Comparisos of the effects of clonidine on pre- and postsynaptic adrenoceptors in the rabbit pulmonary artery: α-sympathomimetic inhibition of neurogenic vasoconstriction. Naunyn-Schmiedeberg's Arch Pharmacol 285:133–150Google Scholar
  33. Starke K, Endo T, Taube HD (1975a) Relative pre- and postsynaptic potencies of α-adrenoceptor agonists in the rabbit pulmonary artery. Naunyn-Schmiedeberg's Arch Pharmacol 291:55–78Google Scholar
  34. Starke K, Borowski E, Endo T (1975b) Preferential blockade of presynaptic α-adrenoceptors by yohimbine. Eur J Pharmacol 34:385–388Google Scholar
  35. Thomas MR, Calaresu FR (1974) Localization and function of medullary sites mediating vagal bradycardia in the cat. Am J Physiol 226:1344–1349Google Scholar
  36. Torvik A (1956) Afferent connections to the sensory trigeminal nuclei, the nucleus of the solitary tract and adjacent structures. J Comp Neurol 106:51–151Google Scholar
  37. Westlund KN, Coulter JD (1980) Descending projections of the locus coeruleus and subcoeruleus/medial parabrachail nuclei in monkey: Axonal transport studies and dopamine β-hydroxylase immunocytochemistry. Br Res Rev 2:235–244Google Scholar

Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • S. Gurtu
    • 1
  • D. K. Sharma
    • 1
  • J. N. Sinha
    • 1
  • K. P. Bhargava
    • 1
  1. 1.Department of Pharmacology and TherapeuticsKing George's Medical CollegeLucknowIndia

Personalised recommendations