How Are Differentiallynally Positioned Progenitors Affected By Diffusible Signals?

* Interneurons or Pseudopolare (Spelling) cells form all the neural wiring within the CNS. These have two axons (instead of an axon and a dendrite). One axon communicates with the spinal cord; one with either the skin or muscle. These neurons have two processes. (Examples are dorsal root ganglia cells.)

A. Starting at the epiblast, describe five developmental events leading up to the generation of upper motor neurons that reside in layer 5 of the motor cortex.

A study was performed by Merzenich in 1986 in which the index finger of a monkey was amputated, and signals were monitored in the corresponding part of the monkey's corticol map (3). Since the monkey's finger was no longer attached to the body, the logical hypothesis is that there would be no signals coming from the finger's area to the nervous system. However, every time the two fingers adjacent to that of the amputated one were touched, there were nerve impulses in the spinal cord. This led the scientists to believe that there are existing axon branches that become unbranched after normal input ends.

The lateral corticospinal tract controls distal parts of the arms, hands, and fingers that are a part of the lower legs, feet and toes. Signals move down these tracts through a chain of events leading to the final common pathway. The primary motor cortex and supplementary motor cortex send their axons through the corticospinal tract. The axons then make their way through subcortical white matter to the ventral midbrain and enter the cerebral peduncles (in the medulla). Once the axons leave the peduncles, they form the pyramidal tracts. The fibers then cross over and descend to the contralateral spinal cord, consequently forming the lateral corticospinal tract. Other fibers, however, go through the ipsilateral spinal cord and form the ventral corticospinal tract. As the axons make their way down the lateral corticospinal tract, they form synapse with the lower motor neurons in the gray matter of the spinal cord. These lower motor neurons are what control the muscles of the arms, hands and

guiding the regeneration of the axons by serving as a physical conduit. The distal segment of the

Lightly myelinated Aδ fibers and unmyelinated C fibers have thinner axons and a higher threshold of activation. Nociceptors of Aδ fibers can be either mechanosensitive or thermosensitive. Polymodal nociceptors (of C fibers), may respond to both mechanical and thermal stimuli, as well as chemicals [261-263]. When nociceptors are activated, the fibers transmit action potentials along the axon to the spinal cord [264, 265]. The spinal cord mediates sensory and motor communication between the periphery and the brain, and is organized into four regions; cervical, thoracic, lumbar, and sacral. The gray matter contains cell bodies of neurons and glia and is divided into the dorsal horn, intermediate column, lateral horn, and ventral horn. The dorsal horn is comprised of sensory nuclei that receive and process incoming sensory information [266], and like the rest of the spinal gray matter, is organized histologically into parallel laminae based on the size and density of neurons [267]. In general, laminae I to IV are involved in exteroceptive sensation whereas laminae V and VI are involved in proprioceptive sensations [263]. Nociceptors terminate in the dorsal horn laminae in a

2) and in the regulation of zebrafish neurulation by the midline signals. Zebrafish neurulation resembles mammalian secondary neurulation and can be potentially associated with neural tube deffects.

Our focus for this week’s lab was the vertebrate nervous system. The nervous system is composed of two divisions called the central nervous system and the peripheral nervous system. Within these two divisions there are three types of neurons that allow us to recognize changes in our environment and help us to respond accordingly. The three neurons that are found are called sensory neurons, interneurons, and motor neurons.

Precise control over the routes taken by growing neurons is tightly controlled (Steward, 1989). In the brain extracellular cues play an important part prompting attractive or repulsive behaviours in cell migration. In addition, they are necessary for cell adhesion, axon guidance and branching (Erskine & Herrera, 2007). For neurons that navigate over long distances, axons can be guided by chemoattractants that draw axonal navigation in its direction or chemorepellents that deter axonal growth in its region.

To visualize the sections and eventually the SNB neurons we used the computer where the photos were regrouped in a folder. The goal was to count the number of SNB motorneurons in each section and recorded in a chart. Then, we summed up the number of neurons per rat; and times it

Peripheral axons from auditory spiral ganglion neurons project to the organ of Corti and synapse with both inner and outer hair cells prior to the onset of hearing. The developmental processes that determine axon outgrowth are largely unknown, though it is thought that a combination of axon guidance molecules and neurotrophic factors determine the fate of the projections. Here, we use immunofluorescence to show that the P2X3 receptor is expressed in both spiral ganglion neurons and hair cells during cochlear development. Furthermore, we demonstrate that P2X3 expression is nearly ubiquitous among spiral ganglion neurons at E16.5. These results support previous work on the spatial expression of P2X3 during development and serve as a foundation for future examination of the developmental function of P2X3.

After the neural tube forms, the cells’ fates are determined and neurogenesis occurs. Often, this neurogenesis/ cell fate determination stage overlaps with migration. Cell fate determination is regulated by many factors, including extrinsic signaling, intrinsic signaling, location/cell migration pathway, and timing of differentiation. One example of extrinsic signaling is notch signaling. In a proneural cluster, there is initially an equal amount of notch and delta signaling. However, one cell starts expressing a higher amount of delta. This signals the other cell to express a lower amount of delta. The imbalance in signaling is amplified. The cell with a higher amount of delta signaling becomes specified as a neuroblast, and the cell that has higher

The transcription factor Otx2 is prevalently detected in TH+ neurons located ventral–medial VTA neurons, and this distribution is gradually decreased in the central and dorsal–lateral VTA. It has also been shown that Otx2 is sporadically co-expressed with Girk2, while most if not all of the Otx2+ neurons are Calb+, and those located in the ventral VTA are also Ahd2+ (Di Salvio et al., 2010; Liang et al., 1996; Schein et al., 1998; Simeone et al., 2011). Despite this slight anatomical and molecular topography, the cell bodies are still largely intermingled within the midbrain nuclei (Fig 1).

Using the probability distribution, we compared the probabilities in wild type and mutants. For example, UNC-6/Netrin extracellular guidance cues can decreases or increase the probability of UNC-40 activity at each side of the neuron. Thus, this probability is directed as a stochastic process. In more evidence, the probability of axon outgrowth activity in ventral direction is decreased, whereas the probability of axon outgrowth in other directions is increased in mutants (Xu et al., 2009; Kulkarni et al, 2013; Yang et al., 2014; Tang and Wadsworth, 2014). Therefore, the guidance cues control the direction of movement fluctuates over time. We report that this probabilities can cause different regions of the neurons plasma membrane to move in different directions. Thus the axon outgrowth extension morphology is abnormal and cause new axon outgrowth patterning.

We determined that knockout of RBM8a in interneuron progenitors alone led to some changes in their distribution, but this effect was significantly less profound as when compared to the deletion of RBM8a from all NSCs. Therefore, we concluded that the phenotype is likely caused by some changes in intrinsic properties, but conceivably as a result of extrinsic cues from excitatory neurons and other cell types.