Expression and impact of Lsamp neural adhesion molecule in the serotonergic neurotransmission system

Pharmacol Biochem Behav. 2020 Nov:198:173017. doi: 10.1016/j.pbb.2020.173017. Epub 2020 Aug 20.

Abstract

Limbic system associated membrane protein (Lsamp) is a neural adhesion protein which has been recently found to be differentially expressed between serotonergic neuron subtypes. We have previously shown elevated serotonin (5-HT) turnover rate in Lsamp-deficient mice. The purpose of the current study was to elucidate the role of Lsamp in serotonergic neurotransmission. Chronic (18 days) administration of serotonin reuptake inhibitor (SSRI) escitalopram (10 mg/kg) significantly increased general activity in wild-type mice in the open field and protected exploration in Lsamp-/- mice in the elevated-plus maze. An important psychopathology-related endophenotype, elevated 5-HT turnover in the brain of Lsamp-deficient mice, was reproduced in the saline group. Escitalopram restored the elevated 5-HT turnover of Lsamp-deficient mice to a level comparable with their wild-type littermates, suggesting that high 5-HT turnover in mutants is mediated by the increased activity of serotonin transporter (SERT protein encoded by Slc6a4 gene). The baseline level of Slc6a4 transcript was not changed in Lsamp-deficient mice, however, our immunohistochemical analysis showed partial co-expression of Lsamp with both SERT and Tph2 proteins in raphe. Overactivity of SERT in Lsamp-/- mice is further supported by significant elevation of Maoa transcript and increase of DOPAC, another Mao A product, specifically in the raphe. Again, elevation of DOPAC was reduced to the level of wild-type by chronic SSRI treatment. The activity of Lsamp gene promoters varied in 5-HT producing nuclei: both Lsamp 1a and 1b promoters were active in the dorsal raphe; most of the expression in the median raphe was from 1b promoter, whereas Lsamp 1a promoter was almost exclusively active in the caudal subgroup of raphe nuclei. We suggest that Lsamp may have an impact on the integrity of serotonergic synapses, which is possibly the neurochemical basis of the anxiety- and sociability-related phenotype in Lsamp-deficient mice.

Keywords: Escitalopram; Limbic system associated protein; Raphe; Serotonin; Serotonin transporter; Tryptophan hydroxylase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Anxiety / drug therapy
  • Anxiety / metabolism*
  • Behavior, Animal / drug effects
  • Cell Adhesion Molecules, Neuronal / genetics
  • Cell Adhesion Molecules, Neuronal / metabolism*
  • Citalopram / administration & dosage
  • Citalopram / pharmacology*
  • Elevated Plus Maze Test
  • GPI-Linked Proteins / genetics
  • GPI-Linked Proteins / metabolism
  • Gene Expression
  • Male
  • Mice
  • Open Field Test
  • Raphe Nuclei / drug effects
  • Raphe Nuclei / metabolism
  • Receptors, Serotonin / metabolism
  • Selective Serotonin Reuptake Inhibitors / administration & dosage
  • Selective Serotonin Reuptake Inhibitors / pharmacology*
  • Serotonergic Neurons / drug effects*
  • Serotonin / metabolism
  • Serotonin Plasma Membrane Transport Proteins / metabolism
  • Synaptic Transmission / drug effects*
  • Tryptophan Hydroxylase / metabolism

Substances

  • Cell Adhesion Molecules, Neuronal
  • GPI-Linked Proteins
  • Receptors, Serotonin
  • Serotonin Plasma Membrane Transport Proteins
  • Serotonin Uptake Inhibitors
  • Slc6a4 protein, mouse
  • limbic system-associated membrane protein
  • Citalopram
  • Serotonin
  • Tryptophan Hydroxylase