title: Experimental evidence that the serotonin transporter mediates serotonin accumulation in LSO neurons of the postnatal mouse.
abstract: During the same postnatal period of development when their terminal projection patterns in the midbrain are maturing, lateral superior olivary (LSO) neurons are immunoreactive for serotonin (5-HT). As there is no evidence that LSO neurons synthesize 5-HT, it is likely that they accumulate 5-HT via the 5-HT transporter. To determine if the 5-HT transporter is responsible for 5-HT inside postnatal mouse LSO neurons, pups (postnatal ages 5-6) were treated with fluoxetine and LSO neurons examined for 5-HT. We also evaluated whether LSO neurons containing 5-HT expressed the 5-HT transporter. To further rule out any potential synthesis of 5-HT, brainstem sections of mice at postnatal ages when 5-HT staining is the most robust were stained for the rate-limiting enzyme in the synthesis of 5-HT, tryptophan hydroxylase. Fluoxetine treatment reduced or in most cases, completely eliminated the number of neurons in the LSO stained for 5-HT. Postnatal LSO neurons containing 5-HT were immunoreactive for the 5-HT transporter; in older animals in which 5-HT was no longer observed in the LSO neurons, 5-HT transporter expression was similarly absent. Further, LSO neurons in mice at any age did not stain for tryptophan hydroxylase. These results indicate that LSO neurons express the functional 5-HT transporter to internalize 5-HT; this mechanism may serve to regulate extracellular 5-HT levels during maturation of their terminal endings in the inferior colliculus.
authors.affiliation: The University of Oklahoma Health Sciences Center, Department of Otorhinolaryngology, Oklahoma City, OK 73126-0901, USA. ann-thompson@ouhsc.edu
authors.forename: Ann M
authors.initials: AM
authors.lastname: Thompson
authors.forename: Glenn C
authors.initials: GC
authors.lastname: Thompson
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D005473:Fluoxetine / Q000494:pharmacology; D007150:Immunohistochemistry; D051379:Mice; D018345:Mice, Knockout; D008995:Monoamine Oxidase / Q000235:genetics; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D009847:Olivary Nucleus / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D011903:Raphe Nuclei / Q000187:drug effects / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000378:metabolism*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D014365:Tryptophan Hydroxylase / Q000378:metabolism
chemical_list: D005473:Fluoxetine; D008995:Monoamine Oxidase; D012701:Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; D017367:Selective Serotonin Reuptake Inhibitors; D014365:Tryptophan Hydroxylase; C493231:Slc6a4 protein, mouse