Commissural neurons

Figure 4. Chemoattraction of spinal cord commissural axons by the floor plate. (A) Axon growth pattern of commissural neurons. (B, C) Collagen gel culture of an alar plate explant with a floor plate explant. Extensive outgrowth of commissural axons occurred toward the floor plate explant (B). Commissural axons were reoriented toward the floor plate explant (C].

Augsburger, A., Schuchardt, A., Hoskins, S., Dodd, J. and Buder, S. (1999). BMPs as mediators of roof plate repulsion of commissural neurons. Neuron 24,127-141. Bernhardt, R.R., Nguyen, N. and Kuwada, J.Y. (1992). Growthcone guidance by floor plate cells in the spinal cord of zebrafish embryos. Neuron 8, 869-882. Bernhardt, R.R., Patel, C.K., Wilson, S.W. and Kuwada, J.Y. (1992). Axonal trajectories and distribution of GABAergic spinal neurons in wild-type and mutant zebrafish lacking floor plate cells. J. Comp. Neurol. 326, 263—272. 

Figure 1. A. SimpMed diagram of the rodent hippocampal formation illustrating the major glutamatergic circuitry. The principal neuronal helds granule cells (GC) of the dentate gyrus and pyramidal cells of CAl and CA3 in Ammon s horn are shown. The main excitatory connections are also indicated the perforant path from entorhinal cortex to the granule cells, from there the mossy hbre (mf) axonal projections to CA3 and then the Schaffer collaterals (Sch) from CA3 to ipsilateral CAl and commissural (Comm) to contralateral CAl cells. Evoked responses in (B) were obtained by stimulating the afferent pathway from entorhinal cortex, the medial perforant path (Med), and recording the granule cell (GC) response in the hilus of the dentate gyrus.

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. 

Mori K, Takagi SF. 1978. Activation and inhibition of olfactory bulb neurones by anterior commissure volleys in the rabbit. J Physiol (Lond) 279 589-604. 

Fig. 13. Basic olfactory network. Schematic of the networks linking the olfactory bulb and primary olfactory cortex. Olfactory nerve axons (ON) terminate in the glomeruli (glom) onto mitral (m) and tufted (t) cells which project via the lateral olfactory tract (LOT) to layer la of primary olfactory cortex to terminate on the dendrites of layer Il-III pyramidal (p) cells. Layer 11-111 pyramidal cells in rostral olfactory cortex project to layer Ib in caudal olfactory cortex and vice versa. Olfactory cortical pyramidal cells also send reciprocal projections back to the olfactory bulb. Thus olfactory bulb output is continuously modified by feedback from areas it targets. Inhibitory interneurons in olfactory bulb and olfactory cortex (shown in gray) modulate network function. Neurons in the ipsilateral (AONi) and contralateral anterior olfactory nuclei (AON) link olfactory networks in the two hemispheres via the anterior commissure.

Haberly, Price and others have systematically studied the organization of intra-PC association and contralateral PC commissural circuits. This associational circuitry is extensive and exhibits a considerable degree of laminar and topographic specificity. These connections arise from pyramidal neurons in layer II and III. Neurons in layer... 

Commissural projections to the contralateral PC originate nearly exclusively from layer II neurons and travel in the anterior commissure [AC]. These projections innervate more posterior parts of the contralateral PC as well as nearby olfactory cortical sites (periamygdaloid cortex, lateral entorhinal cortex, anterior cortical nucleus, nucleus of the lateral olfactory tract) (Haberly and Price, 1978a,b). The caudally-directed commissural projections arise almost entirely from rostral layer lib neurons. However, there are shorter, less extensive commissural projections from caudal PC that target rostrally adjacent regions. This pathway arises mostly from deep layer III neurons although there is a modest contribution from layer II neurons. 

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