Michael W. Jakowec - US grants

DESCRIPTION (provided by applicant): The MPTP-lesioned mouse serves as an excellent model to study the mechanisms involved in the return of striatal dopamine after basal ganglia injury. The administration of MPTP to C57BL/6 mice leads to the destruction of nigrostriatal dopaminergic neurons and subsequent depletion of striatal dopamine. An advantage of MPTP-lesioning is that the degree of neuronal cell death can be titrated such that remaining dopaminergic neurons may act as a template for repair and recovery in response to the injury. Our hypothesis is that glutamate, acting through altered expression of the AMPA-subtype of receptor, activates the transcription factor phospho-CREB and leads to increased tyrosine hydroxylase expression and axonal sprouting in surviving nigrostriatal dopaminergic neurons. This research proposal is designed to define changes that take place after MPTP injury in the expression of AMPA receptors (including their phosphorylated state), the transcription factor CREB, dopamine receptors (Dl, D2, and D3), and the growth-associated protein GAP-43. The effect of blocking glutamate neurotransmission with the AMPA receptor antagonist GYKI-52466 on these parameters will be determined. The molecular tools of immunocytochemistry, western immunoblotting, in situ hybridization, and anterograde labeling will be used to define the mechanisms involved in the return of striatal dopamine. The long-term goal of these studies is to elucidate features of plasticity following injury to the brain and to identify new therapeutic interventions for the treatment of neurodegenerative diseases including Parkinson's disease, Alzheimer's disease, and aging.

Dopamine-glutamate plasticity in nigrostriatal injury: Exercise-enhanced recovery Principal Investigators: Michael Jakowec, PhD, and John Walsh, PhD. University of Southern California. The primary goal of this research proposal is to elucidate the molecular mechanisms underlying the interactions between dopaminergic and glutamatergic neurotransmission and the role that intensive exercise plays in mediating recovery following injury to the nigrostriatal dopaminergic neurons by the neurotoxicant MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine). Previously, in our studies in the MPTP-lesioned mouse model of dopamine depletion we discovered that high-intensity treadmill running, started 5 days post-MPTPlesioning when cell death is complete and continued for 28 days, altered corticostriatal synaptic plasticity in dopaminergic and glutamatergic neurotransmission within the basal ganglia and that these alterations resulted in significant improvement in the recovery of motor performance. We found that motor improvement is not simply due to changes in the total level of striatal dopamine as measured by HPLC analysis, but rather due in part to alterations in dopamine release from remaining nigrostriatal terminals, which is accompanied by increased expression of the dopamine D2 receptor. In addition, both molecular and electrophysiological studies of striatal medium spiny neurons indicated altered glutamatergic neurotransmission specifically increased expression of GluR2 subunits, an important member of the AMPA subtype of glutamate receptor. This proposal will utilize a novel transgenic mouse strain termed BAC-D2-eGFP in which green fluorescent protein is expressed exclusively within the indirect dopamine D2 receptor containing projection neurons of the basal ganglia to determine if exercise-induced changes are pathway specific. Mice will either be administered MPTP or saline and a subset from each group subjected to intensive treadmill exercise for 28 days. This proposal consists of two specific aims.

DESCRIPTION (provided by applicant): Although anabolic-androgenic steroids (AAS) have legitimate medical uses, they are also drugs of abuse. AAS are taken in large quantities by athletes and others to increase performance, with negative long-term health consequences. In 1991, testosterone was declared a controlled substance. Nonetheless, illicit use of AAS continues to increase, particularly among adolescents. Indeed, the incidence of steroid use among high school seniors is comparable to that for cocaine or heroin. Although users defend performance enhancing substances as a "healthy lifestyle choice", clinical studies and anecdotal reports present a different picture. Inappropriate and excessive agonistic behavior ('roid rage) is the most widely-reported psychiatric side effect of AAS in humans. Heightened sexuality and sexual violence have also been noted. Furthermore, AAS are linked with polydrug abuse, most notably opioids. We hope to understand why AAS abuse predisposes individuals to engage in inappropriate and excessive aggression, sexual behavior and drug use, and to unravel the underlying neural mechanisms. In particular, we aim to address a major public misconception that 'roid rage represents a loss of control, a sudden and exaggerated response to a minimal provocation. Instead, research suggests that AAS-treated rats remain sensitive to the context (individual and environment) of social interactions. This suggests a new explanation for behavioral effects of AAS abuse. The current proposal focuses on our hypothesis that chronic exposure to AAS during adolescence inappropriately increases responsiveness to rewarding stimuli, both natural rewards (sex, aggression) and drugs of abuse. The proposed studies will investigate how high-dose androgens in adolescent rats alter reward processes. Understanding behavioral effects of AAS use in humans is complicated by the user's motivation for increased strength and muscle mass. Animal studies can evaluate responses to AAS in an experimental context where appearance and athletic performance are irrelevant. In this regard, animals also demonstrate AAS-induced aggression and sexual behavior. Yet, these studies have emphasized consummatory aspects of behavior, not the appetitive motivation for mating or fighting. Importantly, sex, fighting and drug use are each reinforcing, and each is sensitive to androgens. Accordingly, we hypothesize that AAS increase expression of social behaviors and drug self-administration by increasing the reward value of these steroid-sensitive behaviors. Aim 1 will determine if AAS increase motivation for aggression (Aim 1A), mating (Aim 1B) and morphine self- administration (Aim 1C). Aim 2 will explore neural mechanisms for these effects. We will determine if testosterone is a permissive signal to enhance dopamine activity in the nucleus accumbens in response to sexual stimuli (Aim 2A). Aim 2B will determine fundamental mechanisms underlying these responses by measuring levels of tyrosine hydroxylase, dopamine D1 and D2 receptors, and the dopamine transporter. Together, these studies will provide insight into the potential for AAS to enhance motivation and reward, and the mechanisms through which this occurs. PUBLIC HEALTH RELEVANCE: Illicit use of anabolic-androgenic steroids (AAS) is associated with aggression ('roid rage), sexual violence and polydrug abuse. We will treat adolescent male rats with testosterone to determine if AAS increase motivation for rewarding social behaviors and drug self-administration. According to our hypothesis, testosterone facilitates motivation and reward by enhancing dopamine activity in the nucleus accumbens, through a combination of increased dopamine release, reduced dopamine reuptake, and increased dopamine receptors.

? DESCRIPTION (provided by applicant): Although anabolic-androgenic steroids (AAS) have legitimate medical uses, they are also drugs of abuse. AAS are taken in large quantities by athletes and others to increase performance, with negative long- term health consequences. In 1991, testosterone was declared a controlled substance. Nonetheless, illicit use of AAS continues to increase, particularly among adolescents. Indeed, the incidence of steroid use among high school seniors is comparable to that for cocaine or heroin. Although users defend performance enhancing substances as a healthy lifestyle choice, clinical studies and anecdotal reports present a different picture. Many AAS users meet DSM criteria for psychoactive substance dependence, including continued use despite negative side effects, and withdrawal symptoms when steroids are discontinued. Ultimately, unlike other illicit drugs, AAS have only a limited capacity for acute intoxication. Instead, a key danger of AAS abuse reflects the likelihood that users will engage in behaviors that pose risks to themselves and those around them. Understanding behavioral effects of AAS use in humans is complicated by the user's motivation for increased strength and muscle mass. Furthermore, we cannot control for preexisting psychopathology or for variability in the type or dose of AAS, and it is unethical to test high doses of AAS in normal volunteers. Animal studies can evaluate responses to AAS in an experimental context where appearance and athletic performance are irrelevant. Therefore, we use rats treated chronically with high-dose testosterone to model human AAS use. In humans, AAS increase risk-taking: fighting, unsafe sex, drinking and driving, carrying a weapon. Our studies in rats demonstrate that AAS separately modify decision making on tests of effort, punishment, delay and probability discounting. The proposed studies will build on these recent findings to test the hypothesis that AAS impair complex decision making and cooperation, and these effects are mediated by dopamine (DA) acting via D1- (D1R) and D2-like receptors (D2R) in subnuclei of the nucleus accumbens (Acb). In operant discounting tasks, rats choose between a small reward (1 sugar pellet) vs a large reward (3-4 pellets) which is discounted (made less desirable) by some cost. Chronic high-dose testosterone makes rats less sensitive to physical effort, punishment or delay, but more sensitive to uncertainty. Studies in Aim 1 go beyond simple discounting tasks to model decision-making in a natural environment, presenting cognitively-demanding choices with conflicting costs, and incorporating social interaction. Aim 2 will explore neurobiologic mechanisms for impaired decision making with AAS. As part of the mesolimbic DA system, Acb is central to motivated behavior and decision-making, and DA dysfunction impairs decision making. We will test intra-Acb implants of testosterone (Aim 2A), and pharmacologic manipulation of DAR in Acb during effort- and probability discounting (Aim 2B) and reciprocal cooperation (Aim 2C). Together, these studies will provide insight into the cognitive changes induced by AAS, and the mechanisms through which these occur.