title: Distinguishing characteristics of serotonin and non-serotonin-containing cells in the dorsal raphe nucleus: electrophysiological and immunohistochemical studies.
abstract: The membrane properties and receptor-mediated responses of rat dorsal raphe nucleus neurons were measured using intracellular recording techniques in a slice preparation. After each experiment, the recorded neuron was filled with neurobiotin and immunohistochemically identified as 5-hydroxytryptamine (5-HT)-immunopositive or 5-HT-immunonegative. The cellular characteristics of all recorded neurons conformed to previously determined classic properties of serotonergic dorsal raphe nucleus neurons: slow, rhythmic activity in spontaneously active cells, broad action potential and large afterhyperpolarization potential. Two electrophysiological characteristics were identified that distinguished 5-HT from non-5-HT-containing cells in this study. In 5-HT-immunopositive cells, the initial phase of the afterhyperpolarization potential was gradual (tau=7.3+/-1.9) and in 5-HT-immunonegative cells it was abrupt (tau=1.8+/-0.6). In addition, 5-HT-immunopositive cells had a shorter membrane time constant (tau=21.4+/-4.4) than 5-HT-immunonegative cells (tau=33.5+/-4.2). Interestingly, almost all recorded neurons were hyperpolarized in response to stimulation of the inhibitory 5-HT(1A) receptor. These results suggested that 5-HT(1A) receptors are present on non-5-HT as well as 5-HT neurons. This was confirmed by immunohistochemistry showing that although the majority of 5-HT-immunopositive cells in the dorsal raphe nucleus were double-labeled for 5-HT(1A) receptor-IR, a small but significant population of 5-HT-immunonegative cells expressed the 5-HT(1A) receptor. These results underscore the heterogeneous nature of the dorsal raphe nucleus and highlight two membrane properties that may better distinguish 5-HT from non-5-HT cells than those typically reported in the literature. In addition, these results present electrophysiological and anatomical evidence for the presence of 5-HT(1A) receptors on non-5-HT neurons in the dorsal raphe nucleus.
authors.affiliation: Department of Pediatrics, Joseph Stokes Jr. Research Institute, Abramson Research Center, 4th Floor North, Children's Hospital of Philadelphia, Philadelphia, PA 19104-4318, USA. kirbyl@email.chop.edu
authors.forename: L G
authors.initials: LG
authors.lastname: Kirby
authors.forename: L
authors.initials: L
authors.lastname: Pernar
authors.forename: R J
authors.initials: RJ
authors.lastname: Valentino
authors.forename: S G
authors.initials: SG
authors.lastname: Beck
mesh_terms: D000818:Animals; D004594:Electrophysiology; D007120:Immunochemistry; D008297:Male; D009474:Neurons / Q000737:chemistry* / Q000502:physiology*; D011903:Raphe Nuclei / Q000737:chemistry* / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011985:Receptors, Serotonin / Q000032:analysis / Q000502:physiology; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin / Q000032:analysis / Q000502:physiology*
chemical_list: D011985:Receptors, Serotonin; D044263:Receptors, Serotonin, 5-HT1; D012701:Serotonin