Jill M. Daniel - US grants

DESCRIPTION (provided by applicant) There is growing evidence to indicate that there is an interaction between the biologically active constituent of marijuana, delta 9-tetrahydrocannabinol (delta 9-THC), and the ovarian hormone, estrogen, in the central nervous system. However, little information is currently available regarding the functional consequences of this interaction on behavior. Additionally, despite the fact that the behavioral effects of other drugs of abuse are influenced by estrogenic status, the behavioral effects of delta 9-THC in female animal models have not been investigated. The experiments in the proposed study will test the following hypotheses: 1) Estrogen replacement will attenuate the disruptive effects of systemically administered delta 9-THC on overall response rate and percent errors in ovariectomized rats responding under a multiple schedule of repeated acquisition and performance of behavioral chains. 2) Estrogen replacement will differentially affect levels of cannabinoid receptor binding, as measured by quantitative receptor autoradiography, in brain areas implicated in learning and memory and will potentiate decreases in cannabinoid receptor binding induced by chronic administration of delta 9-THC. 3) Estrogen replacement will accelerate the development of delta 9-THC-induced behavioral tolerance in ovariectomized rats responding under a multiple schedule of repeated acquisition and performance of behavioral chains. 4) Estrogen replacement will attenuate the disruptive effects of intrahippocampally-administered delta 9-THC on overall response rate and percent errors in ovariectomized rats responding under a multiple schedule of repeated acquisition and performance of behavioral chains. These results will provide, for the first time, information regarding the interactive effects of estrogen and delta 9-THC on behavior.

Gonadal hormones can act to permanently organize the brain and behavior. Traditionally, these actions have been thought to occur during a sensitive period early in development. However, results of recent experiments conducted in Dr. Daniel's lab indicate that administration of a transient period of estradiol, the primary estrogen produced by the ovaries, to middle-age rats at the time of cessation of ovarian function results in lasting enhancements on measures of learning and memory that persist well beyond the period of exposure. Furthermore, these enhancements in performance are associated with permanent increases in levels of a type of receptor for estrogen, estrogen receptor alpha (ERá) in the hippocampus, a brain area important for learning and memory. This project will determine the temporal characteristics of the sensitive period following loss of ovarian function during which transient exposure to estradiol can exert lasting effects on cognition and the hippocampus. The project will also determine if permanent changes in levels of ERá mediate the long-term effects exerted on the hippocampus and associated behaviors as a result of a period of transient exposure to estradiol. Lastly, the project will investigate how estrogen receptors can affect cognition in the absence of ovarian estrogens. These experiments will use behavioral, molecular, and electrophysiological techniques to investigate how and under what conditions a transient period of estradiol exposure in adult mammals can permanently affect the brain and behavior. The activities involved in this project will provide increased research opportunities for undergraduate and graduate students from the state of Louisiana, a geographical region that has traditionally been underrepresented in the sciences.

DESCRIPTION (provided by applicant): Estrogen administration begun during a critical window near menopause is hypothesized to prevent or delay age-associated cognitive decline. However, due to potential health risks women often limit use of estrogen therapy to a few years to treat menopausal symptoms. The long-term consequences for the brain of short-term use of estrogens are unknown. The long-term goal of the research is to determine the consequences for the female brain and for female cognitive aging of short-term exposure to estrogens during middle-age such as that used by women during the menopausal transition. The central hypothesis to be tested is that lasting changes in levels of estrogen receptor alpha (ER?) and in the insulin-like growth factor-1 (IGF-1) system in the hippocampus resulting from short-term exposure to exogenously administered estradiol in middle-age following the cessation of ovarian function permanently alters the interaction between ER? and the IGF-1 system in the hippocampus of the aging female brain resulting in increases in levels of ER? target genes and proteins and in enhancement of hippocampus-dependent memory. Guided by preliminary data, this hypothesis will be tested by three specific aims: 1) Determine the nature of the interaction between IGF-1 and ER? in hippocampal neurons; 2) Determine the respective contributions of ER? and IGF-1 receptors in the ability of short-term estradiol exposure to exert lasting impacts on the hippocampus and on hippocampus-dependent memory; and 3) Determine the extent to which the effects of IGF-1 on the hippocampus and on hippocampus-dependent memory in aged females vary dependent upon previous hormone experience. Experiments under the first aim will use primary hippocampal cell cultures to determine the ability of IGF-1 and its signaling pathways to induce ER?-mediated transcriptional activity from an estrogen response element driven reporter gene and to induce activation on of specific phosphorylation sites on ER?. Experiments under the second aim will assess the impact of pharmacological blockage of brain IGF-1 receptors, ER?, or both on the ability of short-term estradiol exposure in middle-aged ovariectomized rats to exert lasting impacts on ER? target genes and associated proteins in the hippocampus and on hippocampus-dependent memory. Experiments under the third aim will determine effects of centrally administered IGF-1 on hippocampus-dependent memory, IGF-1 associated signal transduction pathways, and ER? target genes and associated proteins in aged ovariectomized rats that have and have not undergone estradiol exposure during middle-age. This research is expected to have a positive impact on the study of female cognitive aging by providing elucidation of mechanisms by which a relatively short-term exposure to exogenously administered estradiol during a critical period following the cessation of ovarian function exerts lasting impacts on the hippocampus and on cognition.

PROJECT SUMMARY Males are more likely to engage in risky behaviors that are characterized by lack of behavioral inhibition than are females. In addition, males are more likely than females to be diagnosed with neuropsychiatric disorders that are characterized by decreased behavioral inhibition or impulse control. The basis for this sex difference is likely complex, but is also likely to include a biological component. The long-term goal of the current research is to elucidate brain mechanisms that mediate increased biological vulnerability exhibited by males as compared to females to disorders of impulse control. The prefrontal cortex is thought to influence impulsivity by modulating operations of lower brain areas, including the striatum, that are involved in mediating motor output and reward-based behaviors. Cortical input to the dorsal striatum provides innervation to two primary projection pathways that have opposing effects on behavioral output. Activation of the so-called direct pathway of the striatum facilitates motor output, whereas activation of the indirect pathway inhibits motor output. Coordinated activity of these two pathways is thought to provide for release of desired behaviors while inhibiting undesired ones. The central hypothesis to be tested by the currently proposed experiments is that the relative contributions of the striatal direct and indirect pathways for control of motor output differ between the sexes, with females having increased input from the prefrontal cortex to the dorsal striatum as compared to males allowing for greater cortical control and activation of the striatal indirect pathway over the striatal direct pathway resulting in greater inhibitory control over behavior in females than in males. This hypothesis will be tested by two specific aims. In the first aim, we will determine if males and females have differential levels of prefrontal cortex innervation of direct- and indirect-pathway striatal projection neurons. To achieve this aim, we will use newly available Cre-expressing transgenic rat lines combined with a monosynaptic rabies virus system allowing us to specifically target direct or indirect projection neurons in the striatum and label their monosynaptic inputs. For our second aim, we will determine if the relative contributions of the striatal indirect and direct pathways in the modulation of impulse control varies between males and females. To achieve this second aim, we will use the same transgenic rat lines in combination with designer receptors exclusively activated by designer drugs (DREADD) technology to selectively ?turn off? neurons of the indirect pathway or ?turn on? neurons of the direct pathway and assess levels of impulse control during performance on the 5- choice serial reaction time task, a well-established assay of attentional processes and impulse control in rodents. The completion of the proposed aims will provide the first assessment of potential sex differences in cortical control over direct- and indirect-pathway striatal projection neurons. Results have implications for understanding the biological basis of male vulnerability to disorders of impulse control.