Firing of 5-HT neurones in the dorsal and median raphe nucleus in vitro shows differential alpha1-adrenoceptor and 5-HT1A receptor modulation.
The median raphe nucleus and dorsal raphe nucleus together are the major source of ascending 5-HT projections. Here, using in vitro extracellular single unit electrophysiology we examined the responses of individual neurones in the rat median raphe nucleus and dorsal raphe nucleus to alpha(1)-adrenoceptor and 5-HT(1A) receptor activation and made comparisons between the two nuclei. In the presence of the alpha(1)-adrenoceptor agonist phenylephrine (1microM) all spontaneously active neurones recorded in the median and dorsal raphe nuclei fired slowly (<5Hz) and regularly. Most were inhibited by 5-HT (10-50microM), although a few were excited by 5-HT. 5-HT-induced inhibition was attenuated by the 5-HT(1A) receptor antagonist, WAY100635 (100nM). Compared to those in the dorsal raphe nucleus, the neurones in the median raphe nucleus which were inhibited by 5-HT had: (1) lower basal firing rates in the continuous presence of phenylephrine (1microM), (2) smaller excitatory responses to higher concentrations of phenylephrine (3-10microM), (3) smaller excitatory responses to brief application of norepinephrine (10-100microM) and (4) smaller inhibitory responses to 5-HT (10-50microM). The lower sensitivity of median raphe neurones to alpha(1)-adrenoceptor excitation and 5-HT(1A) receptor inhibition will have consequences for 5-HT neurotransmission in forebrain regions innervated by the two nuclei.
Judge
Sarah J
SJ
Psychobiology Research Group, School of Neurology, Neurobiology and Psychiatry, The Medical School, University of Newcastle upon Tyne, NE2 4HH, UK. s.j.judge@ncl.ac.uk
Gartside
Sarah E
SE
D066298:In Vitro Techniques; D009474:Neurons / Q000502:physiology*; D009638:Norepinephrine / Q000494:pharmacology; D010656:Phenylephrine / Q000494:pharmacology; D011903:Raphe Nuclei / Q000502:physiology*; D044282:Receptor, Serotonin, 5-HT1A / Q000502:physiology*; D018340:Receptors, Adrenergic, alpha-1 / Q000502:physiology*; D012701:Serotonin / Q000502:physiology*
D018340:Receptors, Adrenergic, alpha-1; D044282:Receptor, Serotonin, 5-HT1A; D010656:Phenylephrine; D012701:Serotonin; D009638:Norepinephrine