Elaine M. Hull - US grants

In both humans and rats dopaminergic drugs in small doses facilitate male sexual behavior. In a program designed to locate the sites in the brain at which these drugs act, we have shown that the dopamine (DA) agonist, apomorphine (APO), infused into the medial preoptic area (MPOA), the nucleus accumbens (NA), and the lateral ventricles (LV), affected male sexual behavior in dose related and, at least partially, regionally specific ways. The MPOA is known to be especially important for the regulation of masculine sexual behavior, and our infusions into the MPOA produced more dramatic results than infusions into other areas. One goal of the proposed research is to investigate further the relative importance of the MPOA and of several other DA containing areas (spinal cord, ventral tegmental area, and lateral septal area) in dopaminergic regulation of masculine sexual behavior. A second goal is to specify the receptor mechanisms that mediate the effects of APO infusions. The importance of DA receptors, as opposed to other receptors or nonspecific membrane effects, will be inferred if APO's effects are blocked by a DA receptor antagonist and if infusions of the antagonist produce results opposite to those of APO. In addition, the roles of D-2 receptors and of autoreceptors will be assessed by infusing a specific D-2 agonist and an autoreceptor agonist into the MPOA. A pattern of results similar to APO's, produced by either of these agonists, will suggest that APO acted on the respective receptor. The third goal is to clarify hormone-transmitter interactions and their significance for sexual behavior. The effects of several hormonal manipulations on DA biochemistry and on behavior will be studied. In addition, correlation coefficients will be computed between the resultant biochemical and behavioral changes. Finally, DA biochemistry of inherently good and poor copulators will be compared. Systemically administered DA drugs can facilitate masculine sexual behavior; however, systemically administered drugs affect numerous systems simultaneously. A better understanding of the specific biochemical mechanisms within critical brain areas that regulate masculine function should improve treatment of sexual dysfunction.

Dopaminergic drugs are used to treat impotence; however, their side effects make current treatments less than ideal. This research will provide insights into mechanisms controlling sexual desire, erection, ejaculation, and somatomotor patterns, and should contribute to more specific treatment for sexual dysfunctions. In addition, it will provide insights into several basic issues: how hormones facilitate behavior; how the recently discovered messenger molecule, nitric oxide, may affect neurotramitter release and thereby contribute to sexual behavior; how sexual experience results in long term neural and behavioral changes; and how two major integrative systems interact to enhance sexual behavior. This work presents a conceptual model of three integrative systems that control motivated behaviors. It focuses on one of those integrative hubs, the medial preoptic area (MPOA). This brain area is critical for male sexual behavior in all vertebrate species that have been tested. Dopamine released in the MPOA of male rats during copulation facilitates sexual behavior. The proposed research addresses some of the specific causes and consequences of that dopamine release. 1. What internal factors regulate release of dopamine in the MPOA? The first experiments will test effectiveness of testosterone and of nitric oxide in enhancing dopamine release in the presence of a receptive female. Microdialysis will be used to measure transmitter release in the MPOA of castrates before and after testosterone replacement. Microdialysis will also be used to administer drugs affecting nitric oxide synthesis, and to measure transmitter release in the same area. Drugs diffuse out of, and transmitters diffuse into, the dialysis medium circulating through the dialysis probe. Transmitters will be assayed using HPLC with electrochemical detection. In addition, transmitter release in the presence of a receptive female will be compared in sexually experienced and naive male rats. 2. Are there long term effects of copulation-induced dopamine activity? Synaptic activity may lead to long term neural and behavioral changes by activating certain genes. Copulation activates one such gene, c-fos, in several sites including the MPOA. We will test whether blocking one subtype of dopamine receptor (D1) will block the c-fos expression, and/or the enhancement of copulatory efficient produced by sexual experience. 3. Does dopamine activity in the MPOA affect activity in the mesolimbic system? The MPOA may enhance sexual motivation by facilitating dopamine release in the mesolimbic system, which is thought to increase general activation. Changes in dopamine release in the mesolimbic system, produced by stimulating or blocking dopamine receptors in the MPOA, will be measured. This will test whether the MPOA may increase sexual motivation by activating the mesolimbic system.

Dopaminergic drugs are used to treat impotence; however, their side effects make current treatments less than ideal. This research will provide insights into mechanisms controlling sexual desire, erection, ejaculation, and somatomotor patterns, and should contribute to more specific treatment for sexual dysfunctions. In addition, it will provide insights into several basic issues: how hormones facilitate behavior; how the recently discovered messenger molecule, nitric oxide, may affect neurotramitter release and thereby contribute to sexual behavior; how sexual experience results in long term neural and behavioral changes; and how two major integrative systems interact to enhance sexual behavior. This work presents a conceptual model of three integrative systems that control motivated behaviors. It focuses on one of those integrative hubs, the medial preoptic area (MPOA). This brain area is critical for male sexual behavior in all vertebrate species that have been tested. Dopamine released in the MPOA of male rats during copulation facilitates sexual behavior. The proposed research addresses some of the specific causes and consequences of that dopamine release. 1. What internal factors regulate release of dopamine in the MPOA? The first experiments will test effectiveness of testosterone and of nitric oxide in enhancing dopamine release in the presence of a receptive female. Microdialysis will be used to measure transmitter release in the MPOA of castrates before and after testosterone replacement. Microdialysis will also be used to administer drugs affecting nitric oxide synthesis, and to measure transmitter release in the same area. Drugs diffuse out of, and transmitters diffuse into, the dialysis medium circulating through the dialysis probe. Transmitters will be assayed using HPLC with electrochemical detection. In addition, transmitter release in the presence of a receptive female will be compared in sexually experienced and naive male rats. 2. Are there long term effects of copulation-induced dopamine activity? Synaptic activity may lead to long term neural and behavioral changes by activating certain genes. Copulation activates one such gene, c-fos, in several sites including the MPOA. We will test whether blocking one subtype of dopamine receptor (D1) will block the c-fos expression, and/or the enhancement of copulatory efficient produced by sexual experience. 3. Does dopamine activity in the MPOA affect activity in the mesolimbic system? The MPOA may enhance sexual motivation by facilitating dopamine release in the mesolimbic system, which is thought to increase general activation. Changes in dopamine release in the mesolimbic system, produced by stimulating or blocking dopamine receptors in the MPOA, will be measured. This will test whether the MPOA may increase sexual motivation by activating the mesolimbic system.

Dopamine (DA) is released in the medial preoptic area (MPOA) of male rats in the presence of a receptive female, and it facilitates their copulation. Precopulatory DA release is highly predictive of copulatory ability. Testosterone (T) increases basal and female-stimulated DA release by up-regulating nitric oxide synthase (NOS), which produces nitric oxide (NO), which in turn increases DA release. We will now determine the hormonal and cellular factors that regulate DA release in the MPOA and will also determine the consequences of MPOA DA release on amino acid neurotransmitters. Aim 1 will determine whether T metabolites applied directly to the MPOA can maintain copulation, DA release, NOS immunoreactivity and DA receptors. We will also test whether androgen receptor-containing neurons in the MPOA are also immunoreactive for subtypes of DA receptors and whether castration affects those receptors. Aim 2 will determine the cellular factors that regulate the release of dopamine in the MPOA and the immediate consequences of DA release. Interactions with cGMP, glutamate, and GABA will be studied with both microdialysis and immunocytochemistry. Aim 3 will test mechanism(s) by which sexual experience may facilitate copulation. We will test whether basal or female-stimulated MPOA DA levels are higher in experienced than in naive males and whether injection of an NMDA antagonist into the MPOA prevents the facilitative effects of repeated exposures to a female. Aim 4 will determine the nature and functional significance of a major input to the MPOA. Lesions of the medial amygdala (MeA) blocked the MPOA DA response to a female and impaired copulation. Microinjection of a DA agonist into the MPOA restored copulatory ability in males with MeA lesions. We will now test whether electrical stimulation of the MeA increases DA, glutamate, and/or GABA release in the MPOA and whether axons from the MeA end near MPOA neurons that are immunoreactive for glutamate or GABA receptors or NOS. Two major clinical treatments for erectile disorder either prolong NO's peripheral and central effects or stimulate DA receptors; however, both have undesirable side effects. This research may lead to better treatments for sexual dysfunctions with fewer side effects.

Mating is a socially rewarding experience that may exert protective benefits to health and fitness and buffers against the deleterious effects of stress across a number of mammalian and non-mammalian species. However, the neurobiological mechanisms that underlie these effects are poorly understood, and studies inclusive of female subjects are extremely limited. Using both male and female rodent models, the investigators will utilize a combination of behavioral, cellular, and neurochemical studies to better understand the impact of mating history on stress-related systems. In-vivo neurochemical studies will also allow for the collection and analysis of neurotransmitter release in awake and behaving animals during mating and a stressful encounter. Mating history is expected to dampen stress reactivity through neurochemical changes in regions of the brain that differ between males and females, and differences may be observed between males and females. The evolutionary advantage for the anxiety-reducing, stress-buffering, and rewarding aspects of mating may be to increase an animal's willingness to explore new environments to search for mating partners, and thus facilitate reproduction and ultimately pass on its genes. This research will advance a broader scientific field that includes our understanding of differences between males and females and similarities in the behavioral and neurobiological systems regulating stress and reproduction and how these systems interact. In addition, it will have a broader impact on a number of undergraduates who are trained in neuroscience research in this lab. These students currently include members of groups traditionally underrepresented in science. Further, the investigators will talk to K-12 students about the dissertation research and teach basic neuroscience through outreach activities including Brain Awareness Week and the North Florida Brain Bee, to promote scientific interest in the local community.