Publication Date

2009-06-10

Availability

Open access

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Neuroscience (Medicine)

Date of Defense

2009-05-29

First Committee Member

Robert W. Keane - Committee Chair

Second Committee Member

Edward J. Green - Committee Member

Third Committee Member

Charles W. Luetje - Committee Member

Fourth Committee Member

Dalton Dietrich - Committee Member

Fifth Committee Member

Yossef Itzhak - Mentor

Abstract

Multiple interactions between dopamine (DA), glutamate, and nitric oxide (NO) in mesolimbic and corticostriatal circuits suggest that NO may play a critical role in cocaine-induced behavioral and neural plasticity. Clinical and preclinical studies have revealed that females and adolescents display unique vulnerabilities to the behavioral and neurochemical effects of cocaine as a result of sex-dependent and ontogeny-dependent differences in dopaminergic systems. Thus, my research objectives were to investigate the contributions of the neuronal nitric oxide synthase (nNOS) gene, ontogeny, and gender on the rewarding and sensitizing effects of cocaine. I found that nNOS significantly influences the rewarding aspects of cocaine in adolescent mice and adult male mice (i.e., major deficits in several phases of cocaine conditioned place preference (CPP) were detected in nNOS knockout (KO) adolescent mice and nNOS KO adult male mice). However, the contribution of nNOS was sex-dependent as CPP phases were normal in KO adult females. In contrast to CPP, I found a major ontogeny-dependent contribution of nNOS to the sensitizing effects of cocaine. Namely, while nNOS is essential for the development of behavioral sensitization in adult males, this type of behavioral plasticity develops independently of nNOS during adolescence. The contribution of nNOS was once again sex-dependent as behavioral sensitization was normal in adult KO females. Together, this line of investigation has revealed that the NO-signaling pathway has a) a sex-dependent role in the neuroplasticity underlying cocaine CPP and b) a sex-dependent and ontogeny-dependent influence on cocaine-induced behavioral sensitization. Stereological and western blot analysis revealed that a sensitizing regimen of cocaine resulted in an increase in nNOS and tyrosine hydroxylase (TH) immunoreactivity in the dorsal striatum (dST) of adult, but not adolescent, wild-type (WT) male mice. In the absence of nNOS, dopaminergic neurons in the ventral tegmental area (VTA) were severely reduced and cocaine caused a downregulation of dST TH suggesting that nitrergic levels modulate TH. Thus, the finding that nNOS is essential for the development of sensitization in adulthood, but not adolescence, together with the fact that cocaine upregulated nNOS and TH in the dST in adult, but not adolescent mice, strongly suggest that the nitrergic system underlies behavioral sensitization through modulation of the dopaminergic system in adulthood. These findings suggest different approaches in the clinical treatment of drug craving and drug-seeking behavior in adolescent and adult patients.

Keywords

Adolescence; Gender Differences; Behavioral Sensitization; Conditioned Place Preference; Ventral Tegmental Area; Dorsal Striatum; Nucleus Accumbens; Prefrontal Cortex; Stereology

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