Median and dorsal raphe neurons are not electrophysiologically identical.
The dorsal (DR) and median raphe (MR) nuclei contain 5-hydroxytryptamine (serotonin, 5-HT) cell bodies that give rise to the majority of the ascending 5-HT projections to the forebrain limbic areas that control emotional behavior. In the past, the electrophysiological identification of neurochemically identified 5-HT neurons has been limited. Recent technical developments have made it possible to re-examine the electrophysiological characteristics of identified 5-HT- and non-5-HT-containing neurons. Visualized whole cell electrophysiological techniques in combination with fluorescence immunohistochemistry for 5-HT were used. In the DR, both 5-HT- and non-5-HT-containing neurons exhibited similar characteristics that have historically been attributed to putative 5-HT neurons. In contrast, in the MR, the 5-HT-and non-5-HT-containing neurons had very different characteristics. Interestingly, the MR 5-HT-containing neurons had a shorter time constant and larger afterhyperpolarization (AHP) amplitude than DR 5-HT-containing neurons. The 5-HT(1A) receptor-mediated response was also measured. The efficacy of the response elicited by 5-HT(1A) receptor activation was greater in 5-HT-containing neurons in the DR than the MR, whereas the potency was similar, implicating greater autoinhibition in the DR. Non-5-HT-containing neurons in the DR were responsive to 5-HT(1A) receptor activation, whereas the non-5-HT-containing neurons in the MR were not. These differences in the cellular characteristics and 5-HT(1A) receptor-mediated responses between the MR and DR neurons may be extremely important in understanding the role of these two 5-HT circuits in normal physiological processes and in the etiology and treatment of pathophysiological states.
Department of Pediatrics, Children's Hospital of Philadelphia and University of Pennsylvania, Philadelphia, Pennsylvania 19104-4318, USA. becks@email.chop.edu
Sheryl G
SG
Beck
Yu-Zhen
YZ
Pan
Adaure C
AC
Akanwa
Lynn G
LG
Kirby
D000818:Animals; D004594:Electrophysiology; D008297:Male; D009474:Neurons / Q000737:chemistry / Q000502:physiology*; D011903:Raphe Nuclei / Q000737:chemistry / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012701:Serotonin / Q000032:analysis
D012701:Serotonin