Dwight Charles German, Ph.D. - US grants

Dysfunction of brain catecholamine (CA)-containing neurons has been linked to both neurologic and psychiatric disease (e.g. Parkinson's disease, Alzheimer's Senile Demewtia, and schizopnrenia). The CA neurons which have been related to such diseases are the midbrain dopamine (DA)-containing neurons of the substantia nigra and ventral tegmental area, and the norepinephrine (NE)-containing neurons of the locus coeruleus (LC). In the human brain, these CA-containing cells decrease in number with aging and especially so with Parkinson's disease. The long term goal of this project is to determine whether changes in CA cell number and/or receptor properties are involved in age- and disease-related changes in human behavior. As a preliminary to this goal, we will first gather normative data on (a) aging, (b) laterality, and (c) racial make-up of CA cell topographies and receptor properties. Second, we will examine parkinsonian brains to determine whether the particular disease symptoms (e.g. tremor, rigidity, akinesia, demential) are correlated with regional CA cell loss. A multidisciplinary approach, combining anatomy, biochemistry and neurology, will be used in this project. Anatomically, midbrain DA and LC-NE neurons will be identified in terms of their containing neuromelanin pigment and the CA synthesizing enzyme, tyrosine hydroxylase. These two CA nuclei will be reconstructed into a three-dimensional space with a state-of-the-art computer graphics system. Biochemically, 3H-spiperone binding in striatal and limbic/cortical DA regions will be used to assay postsynaptic DA receptor number and sensitivity. Neurologically, Parkinsonian patients will be clinically and quantitatively evaluated in terms of their specific disease symptomatology, and their brains subsequently examined anatomically and biochemically, as above. Such an analysis of these nuclei in the human brain will elucidate the basic anatomical features of these cell groups, document topographic changes which accompany aging, provide a possible neuronal basis for specific symptoms in Parkinson's disease, and provide a normative data-base for future research on catecholamine-implicated diseases.

Alterations in catecholaminergic neuron function have been implicated in psychosis and affective disorders. An understanding of catecholamine neuron function may shed light on the neural basis, as well as provide insight for treatment, of these serious diseases. Our goal is to study the mechanisms of action of psychoactive drugs on catecholamine-containing neurons using single cell recording and microiontophoretic techniques in the rat. Based upon research findings in our laboratories, we wish to pursue four major topics. First, we have found that the d- and 1-isomers of amphetamine (AMP) have differential effects in reducing the firing rates of substantia nigra (nucleus A9) and ventral tegmental area (nucleus A10) dopamine (DA) neurons. d-AMP has equipotent effects on A9 and A10 neurons; however, 1-AMP is relatively impotent on A9 neurons, but is quite potent on A10 neurons. We wish to determine why these AMP isomers have differential effects on these two DA nuclei. Second, AMP and non-AMP (e.g. amfonelic acid) CNS stimulants influence DA and norepinephrine (NE) neurons differently. We wish to further study the mechanisms of action of non-AMP CNS stimulants on DA and NE neurons. Third, AMP and non-AMP stimulants release and block DA uptake at DA axon terminal regions. We wish to study whether these drugs also have the same effects at the DA cell body/dendrite region. Finally, biochemical research from our laboratories suggest that centrally acting muscle relaxants (e.g. zoxzxolamine, chlorzoxazone and mephenesin) influence striatal DA mechanisms. We wish to determine whether and by what mechanisms they influence DA and NE impulse flow.

Drugs of abuse produce strong positive reinforcing effects which are mediated, in part, by the ventral tegmental area (VTA) dopaminergic (DA) neurons. Rats, for example, will self-administer heroin or morphine directly into the VTA and systemically administered opioid- or DA-antagonists will attenuate this behavior. Microiontophoretic application of morphine directly onto VTA DA neurons produces excitation which is blocked by the opioid antagonist naloxone. Because these neurons are an important part of the brain's endogenous reward system, drugs which activate them (such as opiates, stimulants, alcohol, and nicotine) possess a high abuse potential. The present grant will utilize the following techniques to characterize the structural properties of the endogenous opioid systems which regulate VTA DA neuronal output in the rat: (1) light microscopic immunohistochemical staining techniques will be used to determine the location of the axon terminals of the three opioid peptide-containing neurons (enkephalin, beta-endorphin and dynorphin) within the 3-dimensional space of the VTA; (2) electron microscopic immunohistochemical staining techniques will be used to determine whether the opioid synaptic contacts are made with DA and/or non-DA neurons within the VTA; (3) retrograde neuroanatomical tracing and in situ hybridization techniques will be used together to determine the location of the opioid peptide-containing somata which innervate the VTA; and (4) quantitative receptor autoradiography techniques will be used to determine the location of the opioid receptor subtypes (mu delta, kappa) within the 3-dimensional space of the VTA, and their numbers and affinities. Elucidation of the structural relationships between the opioid and VTA DA neurons will provide an important step toward understanding the neuronal circuits which make up the brain's endogenous reward mechanism/s, and provide a foundation for rational drug abuse treatment approaches.