The OBJECTIVE of this proposal is to characterize serotonergic (5-HT) projections to forebrain in terms of anatomic and pharmacologic properties that influence cortical function. This project will test the HYPOTHESIS that there are DUAL ASCENDING 5-HT PROJECTIONS which differ in cells of origin, axon morphology, and sensitivity to mood-altering drugs. Anatomic data for two dissimilar 5-HT neuronal systems is supported by evidence that particular psychotropic amphetamines act selectively upon a subset of 5-HT axons, causing 5-HT release followed by terminal degeneration. The present study will (1) analyze the anatomic organization of ascending 5-HT projections, (3) identify the terminal morphology and chemical features of 5-HT axons, and (3) assess regeneration of 5-HT axons after their selective ablation.
The AIMS are: 1) to describe the ORIGIN OF 5-HT ORIGIN OF 5-HT PROJECTIONS to selected forebrain areas, and to verify whether the two axon types CONSISTENTLY arise from separate raphe nuclei (DR vs. MR-B9). One class of 5-HT axons will be ablated by neurotoxic amphetamine derivatives; those raphe cells which retain their projections to forebrain will then be located by retrograde axonal transport methods. In addition, to ascertain whether separate raphe nuclei receive different inputs, retrograde transport will be used to identify the source of afferents to each of the midbrain raphe nuclei. 2) Highly-specific antibodies against glutaraldehyde-conjugated 5-HT (and other indoleamines) will be used to detect CHEMICAL DIFFERENCES between raphe neurons. Utilizing these antisera after glutaraldehyde fixation, the morphology of 5-HT SYNAPTIC TERMINALS will be analyzed by confocal and ELECTRON MICROSCOPY. 3) Re- innervation by 5-HT axons will be studied 6-12 months after neurotoxin treatment to identify WHICH RAPHE CELLS UNDERGO SPROUTING, and to determine factors which influence axon regeneration. Quantitative morphometric methods will be used to map retrogradely labeled raphe cell bodies and to measure 50HT axon density. 5-HT projections influence cortical excitability and may be implicated in several neuropsychiatric conditions, particularly dementias and affective disorders. Evidence that many mood- elevating drugs act at 5-HT synapses supports the hypothesis that 5-HT neurons regulate affective state. The identification of dual 5-HT projections that have different chemical and anatomic properties should improve our understanding of the neural mechanisms of mental function and facilitate the treatment of effective and cognitive disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS015199-11
Application #
3396055
Study Section
Neurological Sciences Subcommittee 1 (NLS)
Project Start
1979-03-01
Project End
1995-03-31
Budget Start
1991-04-01
Budget End
1992-03-31
Support Year
11
Fiscal Year
1991
Total Cost
Indirect Cost
Name
Johns Hopkins University
Department
Type
Schools of Medicine
DUNS #
045911138
City
Baltimore
State
MD
Country
United States
Zip Code
21218
Wilson, M A; Molliver, M E (1994) Microglial response to degeneration of serotonergic axon terminals. Glia 11:18-34
Series, H G; Molliver, M E (1994) Immunocytochemical evidence for serotonergic neurotoxicity of N-ethyl-methylenedioxyamphetamine (MDE). Exp Neurol 128:50-8
Wilson, M A; Mamounas, L A; Fasman, K H et al. (1993) Reactions of 5-HT neurons to drugs of abuse: neurotoxicity and plasticity. NIDA Res Monogr 136:155-78;discussion 178-87
Mamounas, L A; Mullen, C A; O'Hearn, E et al. (1991) Dual serotoninergic projections to forebrain in the rat: morphologically distinct 5-HT axon terminals exhibit differential vulnerability to neurotoxic amphetamine derivatives. J Comp Neurol 314:558-86
Wilson, M A; Molliver, M E (1991) The organization of serotonergic projections to cerebral cortex in primates: retrograde transport studies. Neuroscience 44:555-70
Molliver, M E; Berger, U V; Mamounas, L A et al. (1990) Neurotoxicity of MDMA and related compounds: anatomic studies. Ann N Y Acad Sci 600:649-61;discussion 661-4
Molliver, M E; Mamounas, L A; Wilson, M A (1989) Effects of neurotoxic amphetamines on serotonergic neurons: immunocytochemical studies. NIDA Res Monogr 94:270-305
Lyons, W E; Grzanna, R (1988) Noradrenergic neurons with divergent projections to the motor trigeminal nucleus and the spinal cord: a double retrograde neuronal labeling study. Neuroscience 26:681-93
O'Hearn, E; Battaglia, G; De Souza, E B et al. (1988) Methylenedioxyamphetamine (MDA) and methylenedioxymethamphetamine (MDMA) cause selective ablation of serotonergic axon terminals in forebrain: immunocytochemical evidence for neurotoxicity. J Neurosci 8:2788-803
Blue, M E; Yagaloff, K A; Mamounas, L A et al. (1988) Correspondence between 5-HT2 receptors and serotonergic axons in rat neocortex. Brain Res 453:315-28

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