We prepared a monoclonal antibody to microtubule-associated protein 1 (MAP 1), one of the two major high molecular weight MAP found in microtubules isolated from brain tissue . We found that MAP 1 can be resolved by SDS PAGE into three electrophoretic bands, which we have designated MAP ]A, MAP 113, and MAP 1 C in order of increasing electrophoretic mobility. Our antibody recognized exclusively MAP 1A, the most abundant and largest MAP 1 polypeptide . To determine the distribution of MAP 1A in nervous system tissues and cells, we examined tissue sections from rat brain and spinal cord, as well as primary cultures of newborn rat brain by immunofluorescence microscopy. Anti-MAP 1 A stained white matter and gray matter regions, while a polyclonal anti-MAP 2 antibody previously prepared in this laboratory stained only gray matter . This confirmed our earlier biochemical results, which indicated that MAP 1 is more uniformly distributed in brain tissue than MAP 2 (Vallee, R . B., 1982, /. Cell Biol., 92 :435-442) . To determine the identity of cells and cellular processes immunoreactive with anti-MAP 1A, we examined a variety of brain and spinal cord regions . Fibrous staining of white matter by anti-MAP 1A was generally observed . This was due in part to immunoreactivity of axons, as judged by examination of axonal fiber tracts in the cerebral cortex and of large myelinated axons in the spinal cord and in spinal nerve roots . Cells with the morphology of oligodendrocytes were brightly labeled in white matter . Intense staining of Purkinje cell dendrites in the cerebellar cortex and of the apical dendrites of pyramidal cells in the cerebral cortex was observed . By double-labeling with antibodies to MAP 1A and MAP 2, the presence of both MAP in identical dendrites and neuronal perikarya was found. In primary brain cell cultures anti-MAP 2 stained predominantly cells of neuronal morphology . In contrast, anti-MAP 1A stained nearly all cells . Included among these were neurons, oligodendrocytes and astrocytes as determined by double-labeling with anti-MAP 1A in combination with antibody to MAP 2, myelin basic protein or glial fibrillary acidic protein, respectively . These results indicate that in contrast to MAP 2, which is specifically enriched in dendrites and perikarya of neurons, MAP lA is widely distributed in the nervous sytem .Microtubules purified from a variety of sources have been shown to consist of both tubulin, the principal structural protein, and a diverse group of microtubule-associated proteins, or MAP (5,6,27,34,45,46). The MAP have been implicated in the regulation ofmicrotubule assembly (26,46), and. in mediating the interaction of microtubules with other structural elements ofthe cytoplasm (1,3,12,13,15,22,32,33,35). In brain, the most prominent MAP are high molecular weight proteins . These proteins have been divided into two classes, MAP 1 and MAP 2, on the basis oftheir electrophoretic mobility (34). MAP 2 (M, 270,000) remains soluble when microtubules are exposed to elevated temperatur...

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The organization of intrinsic axonal projections of principal neurons in the main olfactory bulb (MOB) was studied in hamsters by using wheat germ agglutinin-horseradish peroxidase (WGA-HRP) and fluorescent dyes. Punctate injections of either WGA-HRP or fast blue (FB) that are restricted to small sectors on one side of the MOB produce comparably restricted fields of retrograde labeling on the opposite side. Label is found predominantly in superficially situated (middle and external) tufted cells that lie near and at the border between the external plexiform and glomerular layers. Few of the deeper middle tufted, internal tufted, or mitral cells and no external tufted cells that lie in the superficial two-thirds of the glomerular layer are labeled in regions remote to the injection site. Anterograde transport of WGA-HRP from the injection site labels axons that travel dorsally and ventrally in restricted bands through the internal plexiform layer and then terminate within this layer in the punctate sector on the opposite side that contains retrogradely labeled neurons. Such reciprocal projections between opposing regions of the medial and lateral sides of the MOB are found at all rostrocaudal and dorsoventral levels. When punctate injections of FB into the MOB are paired with restricted injections of a second fluorescent tracer (nuclear yellow or diamidino yellow dihydrochloride) into the appropriate sector of pars externa (pE) of the anterior olfactory nucleus, the punctate region of remote retrogradely labeled principal neurons is embedded within a topographically restricted longitudinal wedge of retrogradely labeled mitral and tufted cells that project extrinsically to or through pE. However, extremely few of these neurons are double-retrogradely labeled. The results reveal the existence of an intrabulbar associational system in which principal neurons engage in point-to-point, reciprocal projections between opposing regions of the medial and lateral MOB. Moreover, the results indicate that this associational system largely arises from superficially situated tufted cells distinct from those that support bulbofugal projections into the topographically organized interbulbar commissural system via pE.

The organization of connections between the main olfactory bulb (MOB) and pars externa (pE) of the anterior olfactory nucleus was studied in hamsters by using wheat germ agglutinin-horseradish peroxidase as both an anterograde and a retrograde neuronal tracer. Bulbar efferents of pE project exclusively to the contralateral MOB. A topographic organization is evident in these efferents, such that distinct sectors of pE project predominantly to certain sectors of the contralateral MOB and lightly to other sectors. The predominant projection to any bulbar sector in the coronal plane is repeated at nearly all rostral-caudal levels, i.e., the pE efferents to the contralateral MOB terminate within long strips or wedges that show a sector-to-sector topographic organization with respect to the medial-lateral and dorsal-ventral axes but not the rostral-caudal axis of the MOB. Afferents to pE arising in the ipsilateral MOB also show a sector-to-sector topographic organization. Injections into restricted sectors along the circumference of pE label all classes of output neurons (mitral cells and internal, middle, and external tufted cells) in restricted sectors of the ipsilateral MOB, and the sectors that have retrograde neuronal labeling are homotopic to those in the contralateral MOB that have dense anterograde terminal labeling. External tufted cells are not labeled and the other classes of MOB output neurons do not have prominent topographic patterns of labeling in cases with injections caudal to pE. The somata of external tufted cell that project to pE are predominantly in the deep part of the glomerular layer; most of the external tufted cells that lie more superficially in the glomerular layer do not appear to have projections extrinsic to the MOB. These results indicate that both the afferent and efferent connections of pE with the MOB are topographically organized and provide a short synaptic pathway between homotopic sectors of the two main olfactory bulbs.

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