Neuroplasticity in the mesolimbic system induced by natural reward and subsequent reward abstinence.
BACKGROUND
Natural reward and drugs of abuse converge on the mesolimbic system, where drugs of abuse induce neuronal alterations. Here, we tested plasticity in this system after natural reward and the subsequent impact on drug responses.


METHODS
Effects of sexual experience in male rats on behavioral sensitization and conditioned place preference associated with d-amphetamine (AMPH) and Golgi-impregnated dendrites and spines of nucleus accumbens (NAc) cells were determined. Moreover, the impact of abstinence from sexual behavior in experienced males on these parameters was tested.


RESULTS
First, repeated sexual behavior induced a sensitized locomotor response to AMPH compared with sexually naive control subjects observed 1, 7, and 28 days after last mating session. Second, sexually experienced animals formed a conditioned place preference for lower doses of AMPH than sexually naive males, indicative of enhanced reward value of AMPH. Finally, Golgi-Cox analysis demonstrated increased numbers of dendrites and spines in the NAc core and shell with sexual experience. The latter two alterations were dependent on a period of abstinence of 7-10 days.


CONCLUSIONS
Sexual experience induces functional and morphological alterations in the mesolimbic system similar to repeated exposure to psychostimulants. Moreover, abstinence from sexual behavior after repeated mating was essential for increased reward for drugs and dendritic arbors of NAc neurons, suggesting that the loss of sexual reward might also contribute to neuroplasticity of the mesolimbic system. These results suggest that some alterations in the mesolimbic system are common for natural and drug reward and might play a role in general reinforcement.
Pitchers
Kyle K
KK
Department of Anatomy and Cell Biology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
Balfour
Margaret E
ME
Lehman
Michael N
MN
Richtand
Neil M
NM
Yu
Lei
L
Coolen
Lique M
LM
D000578:Amidines / Q000494:pharmacology; D000661:Amphetamine / Q000494:pharmacology; D000704:Analysis of Variance; D000818:Animals; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D003216:Conditioning, Operant / Q000187:drug effects / Q000502:physiology*; D003712:Dendrites / Q000378:metabolism / Q000648:ultrastructure; D004305:Dose-Response Relationship, Drug; D008032:Limbic System / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009043:Motor Activity / Q000187:drug effects / Q000502:physiology; D009473:Neuronal Plasticity / Q000187:drug effects / Q000502:physiology*; D009714:Nucleus Accumbens / Q000166:cytology / Q000187:drug effects / Q000254:growth & development; D051381:Rats; D017207:Rats, Sprague-Dawley; D012201:Reward; D012726:Sexual Behavior, Animal / Q000187:drug effects / Q000502:physiology*; D016622:Silver Staining / Q000379:methods; D013997:Time Factors
D000578:Amidines; D000697:Central Nervous System Stimulants; C046728:2,2'-azobis(2-amidinopropane); D000661:Amphetamine