Kenneth E. Moore - US grants

The long-term objective of this project is to characterize the properties of different dopamine (DA)-and 5-hydroxytryptamine (5 HT)-containing neuronal systems in the rat brain. The hypothesis that will be tested is that anatomically distinct DA and 5HT neuronal systems in the brain subserve different functions and, in turn, are regulated by different mechanisms. Once the properties of the different DA and 5HT neuronal systems are characterized, and differences in the manner by which they are regulated are identified, it may be possible to utilize this information to develop drugs that will influence the activity of one neuronal system without altering the others. Such drugs may be therapeutically useful in treating mental and endocrine disorders. The characteristics of DA neurons in the major ascending mesotelencephalic systems will be compared with the little studied DA neurons which comprise the incertohypothalamic and tuberohypophysial systems. In addition, the characteristics of the major 5HT neuronal systems which originate in raphe nuclei will be compared with the recently described intrahypothalamic 5HT neurons. The activities of these various neurons will be estimated by measuring a) the concentration of metabolites (DOPAC, 5HIAA), b) rates of turnover (decline of DA after administration of a tyrosine hydroxylase inhibitor, Alpha-methyltyrosine) and synthesis (accumulation of DOPA and 5HTP following the administration of a decarboxylase inhibitor, NSD 1015) in brain and hypophysial regions that contain terminals of these neurons. The picogram concentrations of the amine neurotransmitters, their precursors, and metabolites in microdissected brain regions will be quantified using radioenzymatic assays and high performance liquid chromatography coupled to electrochemical detectors. The effects of endocrinological and pharmacological manipulations on the activities of the various 5HT and DA neuronal systems will be characterized using the techniques outlined above.

The long-term goal of this project is to examine the biochemical, endocrinological and toxicological effects of drugs which influence catecholaminergic neurons in the central nervous system. Particular attention will be directed toward the actions of drugs which influence tuberoinfundibular and tuberohypophyseal dopaminergic neuronal systems. The characteristics of the neurons in these minor dopaminergic systems will be compared with those in the major nigrostriatal and mesolimbic (meso-telencephalic) dopaminergic systems. Efforts will be made to determine what functions each of these neuronal systems regulate and, in turn, what regulates the activity of these neurons.

Atrial natriuretic factor (ANF), a peptide 'hormone', isolated from atria and hypothalamus, is a potent vasodilator and natriuretic factor. ANF has physiopathologic implications in hypertension, congestive heart failue, and expansion of blood volume. Studies have demonstrated that vasopressin acts to increase the secretion of ANF. Other studies have demonstrated that the administration of ANF attenuates the increase in vasopressin induced by hemorrhage and water deprivation. Thus, it appears that both ANF and vasopressin are components of a negative feedback control system. The hypothesis of the proposed studies is that the action of ANF that inhibit vasopressin secretion is mediated by tuberohypophyseal dopaminergic (THDA neurons in the hypothalamus. We propose that ANF, from either atrial or hypothalamic sites, stimulates the activity of THDA neurons. THDA neurons, in turn, act to inhibit vasopressin secretion. Vasopressin, released into the systemic circulation or via axon collaterals in the hypothalamus, acts to stimulate the secretion of ANF. The proposed studies will utilize neurochemical and radioimmunoassay procedures and were designed to determine if: 1) ANF stimulates the activity of THDA neurons, 2) THDA neurons mediate the ANF-induced inhibition of vasopressin secretion, 3) vasopressin stimulates ANF secretion and THDa neuronal activity, 4) exogenous vasopressin inhibits the hemorrhage- and dehydration-induced increase in endogenous vasopressin secretion 5) vasopressin mediates the hemorrhage- and dehydration-induced increases in ANF secretion and THDA neuronal activity, 6) ANF mediates the hemorrhage- and dehydration-induced increases in THDA neuronal activity.

The long-term objective of this project is to characterize the regulation of different dopaminergic neuronal systems in the rat brain. The hypothesis that will be tested is that anatomically distinct dopaminergic neuronal systems in the brain subserve different function and, in turn, are differentially regulated by afferent neuronal and/or endocrinological systems. Elucidation of these regulatory mechanisms should assist in the development of drugs that can selectively modulate the activity of specific dopaminergic neurons; such drugs should have therapeutic utility in treating neurological, psychiatric and endocrinological disorders. The characteristics of "classical" nigrostriatal dopaminergic neurons will be compared with little-studied hypothalamic dopaminergic neurons that comprise the tuberohypophysial and incertohypothalamic systems. The activities of these neurons will be estimated neurochemcially by measuring rates of synthesis, turnover and metabolism of dopamine in brain regions that contain perikarya and terminals of these neurons. Studies on tuberohypophysial dopaminergic neurons will focus on the inhibitory actions of these neurons on the secretion of pro-opiomelanocortin-derived peptides (primarily alphaMSH) from the intermediate lobe of the pituitary gland. The ability of stressful stimuli and a variety of pharmacological and endocrinological manipulations know to alter putative neurotransmitter systems will be examined for their ability to alter tuberohypophysial dopaminergic neuronal activity and circulating level of alphaMSH. After validating neurochemical methods, appropriate techniques will be selected to evaluate the effect of afferent neuronal projections and the hormonal milieu on the activity of incertohypothalamic dopaminergic neurons. Focus of these studies will be on the ability of pituitary (prolactin, luteinizing hormone) and gonadal (testosterone, estrogen) hormones to modulated the activity of incertohypothalamic dopaminergic neurons in intact and castrated male and female rats.

The properties and functions of dopamine (DA) neurons that comprise the tuberoinfundibular (TI) system are markedly different from those "typical" DA neurons play important roles in maintaining motor (nigrostriatal DA neurons) and basic psychic (mesolimbic- mesocortical DA neurons) functions, whereas TIDA neurons regulate the release of prolactin from the anterior pituitary. In turn, TIDA but not mesotelencephalic DA neurons are tonically activated by prolactin. Recent evidence indicates that TIDA neurons are also regulated by afferent neuronal systems that are activated by suckling and stress. Currently available drugs that facilitate or block DA transmission processes are non-selective in that they affect all DA neuronal systems and can, therefore, cause disturbing motor, psychic and endocrinological side effects. Knowledge of how different DA neuronal systems are regulated should facilitate the development of new drugs that selectively influence the activity or function of one DA neuronal system without altering the others. The long-term objective of this project is to characterize endocrinological and neuronal factors that influence TIDA neurons. The activity of these neurons will be monitored by measuring: 1) the concentration of dihydroxyphenylacetic acid (DOPAC), a major metabolite of DA, and the rates of synthesis and turnover of DA in brain regions that contain the cell bodies (arcuate nucleus) and terminals (median eminence) of these neurons, and 2) the plasma concentrations of prolactin. These measurements will be made following manipulations that alter the functional activities of afferent neuronal systems which project to and regulate TIDA neurons. These manipulations will include activation (electrical stimulation) or destruction (knife cuts or electrolytic lesions) of discrete brain regions that could contain cell bodies or axons of afferent neurons. In this way the distribution and chemical characteristics of neurons that increase (excitatory afferents) or decrease (inhibitory afferents) the activity of TIDA neurons will be determined. The lesions studies will also assist in determining if pharmacological-endocrinological manipulations (e.g., administration of prolactin) and physiological stimuli (e.g., restraint stress) alter the activity of TIDA neurons via afferent neuronal projections.