Serotonergic influence on olfactory learning in the neonate rat

Behav Neural Biol. 1993 Sep;60(2):152-62. doi: 10.1016/0163-1047(93)90257-i.


The role of the serotonergic innervation of the olfactory bulb was examined in neonate rat pups (Sprague-Dawley) by utilizing an olfactory learning paradigm (Sullivan, McGaugh, & Leon, 1991; Sullivan, Wilson, & Leon, 1989). One hundred fifty nanoliters of the neurotoxin 5,7-dihydroxytryptamine (5,7-dHT, 10 micrograms/microliters) was injected into each anterior olfactory nucleus of Postnatal Day 2 (PND 2) pups in order to selectively deplete the serotonergic (5-HT) innervation of the olfactory bulb. On PND 8, control, sham-operated, or 5-HT-depleted pups were presented with stroke (unconditioned stimulus) paired with peppermint odor (conditioned stimulus) or were presented with peppermint alone. Other pups remained naive, i.e., they were not presented with either stroke or odor. The following day, the pups were placed on a mesh screen above two boxes containing either fresh bedding or bedding with peppermint odor for five 1-min trials. Control and sham-operated pups that were previously trained by the odor/stroke paradigm spent significantly more time over the peppermint odor than similarly trained 5-HT-depleted pups, pups trained using the odor only paradigm, or naive pups. Immunocytochemistry verified that the 5,7-dHT injections specifically depleted the 5-HT innervation of the olfactory bulb and left the 5-HT innervation of more caudal levels of the neuraxis (e.g., piriform cortex) intact. The locomotor behavior of the pups was not affected by the 5-HT depletions. This study is the initial investigation to suggest that 5-HT innervation to the olfactory bulb is important in the acquisition or expression of olfactory-based learned behavior in the neonate rat.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • 5,7-Dihydroxytryptamine / pharmacology
  • Aging / drug effects
  • Aging / physiology*
  • Animals
  • Animals, Newborn
  • Association Learning / drug effects
  • Association Learning / physiology
  • Body Weight / drug effects
  • Body Weight / physiology
  • Brain Mapping
  • Conditioning, Classical / drug effects
  • Conditioning, Classical / physiology*
  • Dominance, Cerebral / drug effects
  • Dominance, Cerebral / physiology
  • Female
  • Male
  • Mental Recall / drug effects
  • Mental Recall / physiology*
  • Motor Activity / drug effects
  • Motor Activity / physiology
  • Norepinephrine / physiology
  • Olfactory Bulb / drug effects
  • Olfactory Bulb / physiology*
  • Olfactory Pathways / drug effects
  • Olfactory Pathways / physiology
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Serotonin / drug effects
  • Receptors, Serotonin / physiology*
  • Serotonin / physiology*
  • Smell / drug effects
  • Smell / physiology*
  • Tyrosine 3-Monooxygenase / physiology


  • Receptors, Serotonin
  • 5,7-Dihydroxytryptamine
  • Serotonin
  • Tyrosine 3-Monooxygenase
  • Norepinephrine