The serotoninergic innervation of cerebral cortex: Different classes of axon terminals arise from dorsal and median raphe nuclei
Tóm tắt
The objective of the present study was to characterize the morphology of serotoninergic axons in cerebral cortex of the rat and to determine whether dissimilar axon terminals arise from the dorsal vs. the median raphe nuclei. The anterograde tracer PHA‐L was administered by iontophoresis into the dorsal (DR) and median (MR) raphe nuclei, and the morphologic features of the respective axonal projections from raphe to forebrain were analyzed. We have observed consistent structural differences between the axons from these two nuclei. Anterogradely labeled axons which arise from cells in the MR are characterized by large, spherical varicosities (type M axons) and by variations in axonal diameter. In contrast, DR fibers are very fine and typically have small, pleomorphic varicosities that are granular or fusiform in shape (type D axons). Similar features of serotonin (5‐HT) axon morphology are also evident in 5‐HT immunocytochemical preparations. In addition to structural differences, there is differential topographic distribution of MR vs. DR fibers, with MR axons concentrated in particular areas of limbic cortex such as dentate gyrus, posterior cingulate, and entorhinal areas as well as in parietal cortex. Immunofluorescence with dual labels shows that over two‐thirds of the raphe‐cortical axons are serotoninergic. The dissimilarities in axon morphology indicate that individual raphe nuclei may form different patterns of synaptic organization. Based on the evidence that the dorsal and median raphe nuclei give rise to morphologically different axon terminals, we conclude that 5‐HT axons in cortex may be subdivided into two distinct projections. This proposal is in accord with other, recent data showing that the two axon types have different pharmacologic properties and are likely to be functionally different.
Từ khóa
Tài liệu tham khảo
Dählstrom A., 1964, Evidence for the existence of monoamine‐containing neurons in the central nervous system. I. Demonstration of monoamines in cell bodies of brain neurons, Acta. Physiol. Scand., 62, 1
Fuxe K., 1965, Evidence for the existence of monoamine neurons in the central nervous system. IV. Distribution of monoamine nerve terminal in the central nervous system, Acta. Physiol. Scand., 64, 39
Gerfen C. R., 1982, Immunohistochemical localization of axonally transported PHA‐L lectin to demonstrate the fine morphological details of efferent connection in the CNS, Soc. Neurosci. Abstr., 8, 786
Hsu S. M., 1981, The use of avidin‐biotin peroxidase complex (ABC) in immunoperoxidase techiques: A comparison between ABC and unlabeled antibody (PAP) procedures, J. Histochem. Cytochem., 29, 577, 10.1177/29.4.6166661
Kosofsky B. E., 1984, Organization of ascending dorsal raphe projections in the rat, Soc. Neurosci. Abstr., 10, 288
Molliver M. E., 1982, Cytochemical Methods in Neuroanatomy, 255
O'Hearn E., 1986, Systemic MDA and MDMA, psychotropic substituted amphetamines, produce serotonin neurotoxicity, Soc. Neurosci. Abstr., 12, 1233
Steinbusch H. W. M., 1983, Chemical Neuroanatomy, 131
Steinbusch H. W. M., 1979, Adv. Pharmacol. and Ther., Vol. 2, Neurotransmitters, 151
Steinbusch H. W. M., 1981, The nucleus raphe dorsalis of the rat and its projection upon the caudatoputamen: A combined cytoarchitectonic, immunohistochemical and retrograde transport study, J Physiol. (Paris), 77, 157
Uhl G. R., 1981, Neurosecretion and Brain Peptides, 87
Ungerstedt U.(1971) Stereotaxic mapping of the monoamine pathways in the rat brain.Acta. Physiol. Scand.(Suppl. 367) pp.1–48.