The Journal of comparative neurology
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Comparative Study
Olfactory sensory neuron-specific and sexually dimorphic expression of protocadherin 20.
Olfactory sensory axons navigate from the nasal cavity to the olfactory bulb and sort from among 1,000 different odorant receptor-expressing types to converge upon the same two or three glomeruli. To achieve this task during development, it is likely that multiple classes of regulatory molecules, including cell adhesion molecules, are involved. Cell adhesion molecules have been shown to be important in controlling axon guidance, fasciculation, and synapse formation. ⋯ These small, discrete numbers of PCDH20-positive glomeruli in the adult olfactory bulb are consistently clustered in the ventral-caudal region in both male and female mice. However, adult males have higher numbers of PCDH20-positive glomeruli with a broader distribution, whereas adult females have fewer PCDH20-positive glomeruli with a more restricted distribution. The gender difference in PCDH20 expression may reflect olfactory receptor expression differences for gender-specific social discrimination.
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Comparative Study
Sexual dimorphism in neuronal number of the posterodorsal medial amygdala is independent of circulating androgens and regional volume in adult rats.
The posterodorsal medial amygdala (MePD) in rodents integrates olfactory and pheromonal information, which, coupled with the appropriate hormonal signals, may facilitate or repress reproductive behavior in adulthood. MePD volume and neuronal soma size are greater in male rats than in females, and these sexual dimorphisms are maintained by adult circulating hormone levels. Castration of adult males causes these measures to shrink to the size seen in females 4 weeks later, whereas testosterone treatment of adult females for 4 weeks enlarges these measures to the size of males. ⋯ Males also have more glial cells than do females, but, in contrast to the effects on neuronal number, the number of glial cells is affected by androgen in the right MePD of both sexes and, therefore, may contribute to regional volume changes in adulthood in that hemisphere. Thus, regional volume, neuronal size, and glial numbers vary in the MePD of adult rats in response to circulating androgens, but neuronal number does not. These results suggest that the sex difference in neuronal number in the rat MePD may be "organized" by androgens prior to adulthood, whereas regional volume, neuronal size, and glial numbers can be altered by androgens in adulthood.
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The hypothalamic suprachiasmatic nucleus (SCN) is the primary mammalian circadian clock that regulates rhythmic physiology and behavior. The SCN is composed of a diverse set of neurons arranged in a tight intrinsic network. In the rat, vasoactive intestinal peptide (VIP)- and gastrin-releasing peptide (GRP)-containing neurons are the dominant cell phenotypes of the ventral SCN, and these cells receive photic information from the retina and the intergeniculate leaflet. ⋯ KCC2, a K(+)/Cl(-) cotransporter, was highly expressed in the ventral SCN in association with VIP- and GRP-producing neurons, whereas VP neurons in the dorsal SCN were devoid of KCC2. On the other hand, GABA(B) receptors were observed predominantly in VPergic neurons dorsally, whereas, in the ventral SCN, GABA(B) receptors were associated almost exclusively with retinal afferent fibers and terminals. The differential expression of GABAergic markers within the SCN suggests that GABA may play dissimilar roles in different SCN neuronal phenotypes.
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Chronic nerve compression (CNC) injury initiates a series of pathological changes within the peripheral nerve at the site of injury. However, to date, little work has been performed to explore neuronal cell body responses to CNC injury. Here we show a preferential upregulation of growth-associated protein-43 (GAP-43) and enhanced Fluoro Ruby uptake by the small-diameter calcitonin gene-related protein (CGRP) and isolectin B4 (IB4)-positive neurons in the L4 and L5 ipsilateral dorsal root ganglion (DRG) 2 weeks and 1 month post injury. ⋯ Quantification of glial-derived neurotrophic factor (GDNF) protein revealed an upregulation in L4 and L5 DRG followed by a return to baseline values at later stages following injury. Upregulation of GDNF expression by Schwann cells was also readily apparent with both immunohistochemistry and Western blot analysis of 1 month compressed sciatic nerve specimens. Thus, CNC induces a phenotypic change in the DRG that appears to be temporally associated with increases in GDNF protein expression at and near the site of the compression injury in the nerve.
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Nogo receptors (NgR1, -2, and -3) and their ligands, i.e., myelin-derived neurite outgrowth inhibitor (Nogo)-A, myelin-associated glycoprotein (MAG), and oligodendrocyte myelin glycoprotein (OMgp), have been considered to play pivotal roles in controlling axonal regeneration and neuronal plasticity. We show here that NgR1-3 mRNAs were differentially expressed exclusively in neurons situated in the telencephalon, diencephalons, and cerebellum, whereas we could not detect any NgR1-3 mRNA expression in the mesencephalon, pons, medulla oblongata, and spinal cord. On the other hand, Nogo-A mRNA was abundantly expressed in both neurons and oligodendrocytes throughout the central nervous system (CNS). ⋯ Interestingly, we did not detect NgR1-3 mRNAs in monoaminergic neurons in the substantia nigra, ventral tegmental area, locus caeruleus, and raphe nuclei, which are known to have high regenerative capacity. In addition, although neurons in the reticular thalamus and cerebellar nuclei are also known to show high capacity for regeneration, NgR1-3 mRNAs were not detected there. These data indicate that NgR1-3, Nogo-A, MAG, and OMgp mRNAs are differentially expressed in the rat CNS and suggest that the level of NgR1-3 expression in a neuron might determine its regenerative capacity.