title: Environmental and behavioral modulation of the number of substantia nigra dopamine neurons in adult mice.
abstract: BACKGROUND
  Recent evidence indicates that hypothalamic neurons acquire or lose the capacity to synthesize and release dopamine (DA) in response to environmental stimuli, and this has functional and behavioral consequences for adult rats. We have evidence that neuronal activity, including that driven by afferent input, regulates acquisition and loss of the DA phenotype by substantia nigra pars compacta (SNc) neurons in adult mice. Hypotheses The aims of the present study were to determine whether the environment or behavior regulates the number of SNc DA neurons in adult mice, and whether this is mediated by afferent input.
  
  
  METHODS
  ADULT MICE WERE SUBJECT TO TWO DIFFERENT ENVIRONMENTS/BEHAVIORS: "mating" for 1 week or "environment enrichment" (EE) for 2 weeks; then the numbers of tyrosine hydroxylase (TH, the rate limiting enzyme in DA synthesis) immunopositive (TH+) and immunonegative (TH-) SNc neurons were counted.
  
  
  RESULTS
  More TH+ neurons were present in mated males whereas less TH+ neurons were present in mated females. Also, more TH+ neurons were present in EE males, and this increase was completely abolished by concurrent local infusion of GABAA receptor antagonists.
  
  
  CONCLUSIONS
  The number of DA neurons in the adult SNc is not fixed, but readily increases and decreases in response to environmental stimuli and/or behaviors. These changes are mediated by afferent input relaying information about the environment or behavior to SNc neurons.
authors.affiliation: Florey Institute of Neuroscience and Mental Health, The University of Melbourne Parkville, Victoria, Australia, 3010.
authors.forename: Tim D
authors.initials: TD
authors.lastname: Aumann
authors.affiliation: Florey Institute of Neuroscience and Mental Health, The University of Melbourne Parkville, Victoria, Australia, 3010.
authors.forename: Doris
authors.initials: D
authors.lastname: Tomas
authors.affiliation: Florey Institute of Neuroscience and Mental Health, The University of Melbourne Parkville, Victoria, Australia, 3010.
authors.forename: Malcolm K
authors.initials: MK
authors.lastname: Horne
keywords: Dopamine; midbrain; plasticity