Dendritic Arbors

With very few exceptions, the neurons in the medial, lateral, and anterior cell groups of the AL fall into two main classes (19,65,67,72,73). Projection neurons (PNs or output neurons) have dendritic arborizations in the AL neuropil and axons that project out of the AL, and local... 

Wayman, G. A., Impey, S., Marks, D., Saneyoshi, T., Grant, W. F., Derkach, V. and Soderling, T. R., 2006, Activity-Dependent Dendritic Arborization Mediated by CaM-Kinase I Activation and Enhanced CREB-Dependent Transcription of Wnt-2, Neuron, 50, pp 897-909. 

Detection of mRNA of each cloned DA receptor by means of in situ hybridization is a sensitive and specific methodology. mRNA, however, is almost exclusively contained in the neuronal cell body and, therefore, this technique does not allow the identification of receptors within dendritic arborizations or axon terminals. In addition, the presence of RNA transcript does not allow to determine to what extent the mRNA is translated into protein, and does not always correlate with the presence of active receptor protein or ligand binding sites. 

The efficacy of the spin trapping agent PBN and the antioxidant vitamin E was tested to suppress increase in NO and hpid peroxidation and prevent neurodegeneration of pyramidal neurons in the CAl hippocampal area in the model of KA-induced excitotoxicity. Vitamin E or PBN alone did not alter basal citrulline and F4-NeuroPs levels or dendritic arborization. However, vitamin E and PBN suppressed KA-induced increases in citrulline and cerebral and neuronal markers of oxidative damage, p2-IsoPs and F4-NeuroPs, respectively (Figures 42.8 and 42.9). 

Ohkawa N, Fujitani K, Tokunaga E, Furuya S, Inokuchi K. The microtubule destabilizer stathmin mediates the development of dendritic arbors in neuronal cells. J. CeU Sci. 2007 120 1447-1456. 

Dopaminergic amacrine cells with widespread dendritic arborizations increase release of dopamine in response to increases in global illumination. Dopamine diffuses throughout the retina to influence cells as far away as the RPE. The increased release of dopamine by light modifies cell function to opdmize retinal responses in daylight (Witkovsky, 2004). 

In contrast to M cells, P cells have small cell bodies with small dendritic arborizations resulting in small receptive fields. P cells are also wavelength-selective. P cell output thus contributes to fine feature analysis and color vision. P cells are classified anatomically as midget ganglion cells. 

Figure 14.1. The densities of dendritic arbors lie on a continuum of values. Differences in arbor densities reflect differences in connectivity. [Drawings of neurons from (Ramdn y Cajal, 1995)].

Raz et al (1993) ... leftward volume asymmetry may reflect either a greater number of processing elements or more extensive connectivity in the left hemisphere. Gross hemispheric asymmetries are likely to arise from differences in the number of neurons rather than from altered dendritic arborization or cell packing density. .. the volume advantage is likely to reflect the excess of processing modules (cortical columns) ... 

Is dendritic arborization and synapse number important for variability in cognitive ability (Anderson Donaldson 1995) Zagon has reported that postnatal administration of naltrexone, an opiate receptor antagonist, augments rat brain size and increases cortical neuron dendritic arborization (Hauser et al 1989, Zagon McLaughlin 1984). In MAM-treated rats, I showed that postnatal treatment with naltrexone could ameliorate the behavioural deficit for attention to novelty, habituation performance and response flexibility (see Fig. 5) with intermediate effects on time to perform a reasoning task. 

FIG. 5. The number of errors on an inclined plane response flexibility problem (Thompson et al 1990) is shown for the same groups of animals as seen in Fig. 4. Saline-treated controls made the fewest errors. Animals exposed to the neurotoxin MAM were slower to abandon a previously learned solution to try new routes to food. However, animals treated postnatally with naltrexone, an opiate receptor antagonist reported to induce dendritic arborization and spine formation, showed performance similar to controls. Decreases in neuron number, such as seen with MAM exposure prenatally, have adverse effects on tests of rat intelligence. Treatments that induce dendritic arborization and synapse formation can ameliorate these deficits. The ability to modify brain structure permits direct testing of the causal role of variation in brain structure and behavioural performance. 

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