Fiber commissural

Rat (Wistar) 3 wk 7 d/wk ad lib (W) 15 (increase in volume of mossy fiber zone, granule cell layer, and commissural association zone in hippocampus of offspring) Slomianka et al. 1989 PbAc... 

If a spinal cord is cross-sectioned, the gray matter appears as a roughly H-shaped area in its middle which is, divided into dorsal (posterior), lateral, and ventral (anterior) horns. The horns are interconnected by a crossbar, the gray commissure. The rest of the spinal cord is the white matter, made up largely of tracts of myelinated nerve fibers (axons). Ascending tracts carry afferent sensory impulses towards the brain, descending tracts transmit motor impulses from the brain to the motor neurons in the ventral or lateral horns of the gray matter. 

The dense intermingling of nerve fibers within the WM connects different regions of the brain with each other. Projectional fibers connect cerebral cortex and subcortical structures as well as cerebellum commissural fibers connect homologous areas between the two hemispheres of brain, and the association fibers connect various regions within the same cerebral hemisphere. The major function of the cerebral WM is simply to interconnect various regions of brain and transmit signals in-between them. 

One striking feature of hippocampal circuitry is the pattern of afferent termination. Major hippocampal afferents originating from entorhinal cortex and ipsilateral and contralateral hippocampal subfields synapse on the dendrites of the principal cells in a laminated pattern. For instance, hippocampal commissural and associafional fibers synapse within the proximal one-third of the granule cell dendritic field, which is close to the cell body layer. The massive perforant path fibers terminate topographically in the outer two-thirds of the dendritic field. Afferents also have a laminar organization in the hippocampal proper. 

The CAS pyramidal cells give rise to highly collateralized axons, which project both to within the hippocampus (CAS, CA2 and CAl) and also to the same fields in the contralateral hippocampus via the commissural fibers. Some of the CAS axons project to the lateral septal nucleus. All of the CAS and CA2 pyramidal cells give rise to highly divergent projections to all subfields of the hippocampus. The main afferents to the CAl pyramidal cells come from the Schaffer collateral/... 

Cholinergic Actions in MOB Only limited information is available about cholinergic actions in MOB. Electrical activation of NDB has been reported to depress (Nickell and Shipley, 1988a) or increase (Kunze et al., 1991, 1992) mitral cell activity indirectly via primary effects on GABAergic GCs. NDB stimulation also reduced the field potential in the MOB caused by stimulation of the anterior commissure (Nickell and Shipley, 1993), an effect mediated by presynaptic inhibition of anterior commissure terminals via muscarinic receptors. One interpretation of these results is that cholinergic input to MOB may function to modulate interhemispheric transmission of olfactory information. In this regard, it is noteworthy that anterior commissural fibers are required for access and recall of olfactory memories between the two hemispheres. Infusion of ACh into MOB was reported to reduce paired-pulse depression of lateral olfactory tract (LOT)-evoked field potentials recorded in the GCL. This effect was attributed to... 

Haberly LB, Price JL. 1978a. Association and commissural fiber systems of the olfactory cortex of the rat. I. Systems originating in the piriform cortex and adjacent areas. J Comp Neurol 178 711-740. 

The (central) cerebellar nuclei and the lateral vestibular nucleus of Deiters receive the axons of the Purkinje cells of the cerebellar cortex and serve as the main output stations of the cerebellum. The vermis and the flocculus also project to other vestibular nuclei, but here the Purkinje cell axons compete with vestibular root fibers, intrinsic and commissural vestibular connections and projections from the medial cerebellar nucleus and, therefore, are not the dominant afferent system. 

The AChE-banding pattern in the molecular layer of the anterior vermis and the white matter compartments of the anterior lobe continue, across the primary fissure, into the posterior lobe. A wide A compartment, flanked by diverging X and B compartments is present in the vermis of the simple lobule (Figs 119 and 120). The B compartment ends at the area without cortex in the center of the ansiform lobule, where it abuts on the pontocerebellar fibers of the cerebellar commissure that reach the surface at this point. It is not clear whether the X compartment continues from the simple lobule into lobule... 

The striatum comprises the caudate, putamen and nucleus accumbens. In mammals in which corticofugal fibers coalesce into the internal capsule within the striatum, the caudate nucleus and putamen nucleus are separated by this partition. In animals in which corticofugal fibers are dispersed there is no clear separation between these nuclei, thus the term caudate-putamen is often used. The caudate and putamen, in most species, generally occupy the dorsal part of the striatum. The nucleus accumbens is the rostro-ventral extension of the striatum, and occupies the area surrounding the anterior commissure in the rostral part of the striatum. The term ventral striatum is generally used to refer to the nucleus accumbens and more caudally, the ventral most part of the striatum (Fleimer and Wilson 1975). The olfactory tubercle is sometimes included as a part of the ventral striatum, but in this review will not be discussed. 

Aspartate is closely related metabolically and chemically to glutamate. In many respects it is difficult to differentiate between aspartate and glutamate as neurotransmitter candidates (Fonnum, 1984). There are, however, some fibers and terminals in which aspartate is regarded as a stronger transmitter candidate than glutamate. These include the cerebellar climbing fibers (Wiklund et al., 1982), hippocampal commissural fibers (Nadler et al., 1978), olfactory tract (Collins and Probett, 1981), cochlear nucleus afferents (Wenthold, 1979), and spinal cord intemeurons (Davidoff et al., 1967)... 

Figure 10.18 Metal content is abnormal in PD basal ganglia. Basal ganglia, coronal section normal (N) brain (a)-(c) (expanded view of Figure 10.17) PD brain (d) f). (a), (d) Iron maps (b), (e) zinc map (c) (f) overlay of iron and zinc cn, caudate nucleus p, putamen Igp, lateral globus pallidus mgp, medial globus pallidus 1ml, lateral medullary lamina mml, medial medullary lamina ami, accessory medullary lamina ic, internal capsule ins, insula ot, optic tract ac, anterior commissure vaf, ventral amyg-dalofugal fibers amg, amygdaloid nucleus u, uncus ent, enthorinal cortex hip, hippocampus , blood vessel arrows, perivascular iron scale bar = 5 mm shaded scales (a, b, d, e) represent the normalized total Ka fluorescence counts proportional to total metal present, from...

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