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R B Norgren

Publications and source records attributed to R B Norgren.

29 records · Page 2Linked to original sources
PubMed1992

Development of olfactory nerve glia defined by a monoclonal antibody specific for Schwann cells.

Although there is considerable interest in the possible role of olfactory glia in the pathfinding abilities of olfactory nerve axons, the complete development of these glia in vivo has not been described. Using a specific Schwann cell marker, the 1E8 antibody, we have found that olfactory nerve glia can be identified throughout development. These glia appear to originate in the olfactory placode and migrate initially into the periphery of the olfactory nerve, and later into the center of the nerve. Olfactory nerve glia enter the presumptive olfactory bulb with the olfactory receptor neuron axons and distribute themselves along the edge of the olfactory nerve layer. The fact that olfactory nerve glia are specifically immunostained by the 1E8 monoclonal antibody, which recognizes the Schwann cell-specific protein P0, suggests that these cells more closely resemble Schwann cells than astrocytes or enteric glia. These results support and extend previous findings suggesting that olfactory nerve glia have distinctive developmental and anatomical features which may be important to the regenerative capacity of the olfactory system.

Aging↗
PubMed1992

Anterograde transport of HSV-1 and HSV-2 in the visual system.

The anterograde spread of herpesvirus in the visual system subsequent to retinitis has been observed clinically. We compared the ability of two well-studied Herpes simplex virus (HSV) strains to be transported in the anterograde direction in the hamster visual system: strain McIntyre, representing HSV-1, and strain 186, representing HSV-2. Intravitreal injection of HSV-2 labeled more retinorecipient neurons than did HSV-1, suggesting important type differences in the ability of HSV to infect retinorecipient neurons after intravitreal injection. The most likely explanation for our results is that HSV-2 is more efficiently adsorbed than HSV-1 in the retinal ganglion cells. Our results also suggest that HSV may be useful as an anterograde transneuronal tracer for neuroanatomical studies of the visual system.

Animals↗
PubMed1991

Neurons that migrate from the olfactory epithelium in the chick express luteinizing hormone-releasing hormone.

In several mammalian species, luteinizing hormone-releasing hormone (LHRH) neurons have been shown to migrate from nasal regions to the brain during early development. Using immunocytochemistry, we have identified LHRH containing neurons in developing chick embryos. In embryonic day 4 (E4) and E5 animals, a small group of LHRH immunoreactive (IR) neurons were found just ventral to the olfactory pit. LHRH-IR neurons were also found within the immunoreactive (IR) neurons were found just ventral to the olfactory pit. LHRH-IR neurons were also found within the nasal epithelium. In E6 and E7 animals, many more LHRH-IR neurons were observed in nasal epithelium, in close association with the olfactory nerve, and within the telencephalon. These data are consistent with the hypothesis that LHRH neurons in chicks originate within nasal structures and migrate into the brain.

Animals↗
PubMed1990

Distribution of vasoactive intestinal peptide-like and neurophysin-like immunoreactive neurons and acetylcholinesterase staining in the ring dove hypothalamus with emphasis on the question of an avian suprachiasmatic nucleus.

Two nuclei, termed here the medial hypothalamic nucleus and the lateral hypothalamic retinorecipient nucleus, are possible homologs of the mammalian suprachiasmatic nucleus. As the mammalian suprachiasmatic nucleus is characterized by a dense concentration of vasoactive intestinal peptide (VIP)- and neurophysin (NP)-immunoreactive neurons and an absence of acetylcholinesterase (AChE) staining, we decided to examine these factors in the ring dove hypothalamus. Neither the medial hypothalamic nucleus nor the lateral hypothalamic retinorecipient nucleus contained either VIP- or NP-like immunoreactive neurons. The lateral hypothalamic retinorecipient nucleus stained darkly for AChE. Although there was some overlap in the distribution of VIP- and NP-like immunoreactive neurons, a clustering of both types into a well defined nucleus was not observed. Therefore, an avian homolog to the mammalian suprachiasmatic nucleus must differ in its chemoarchitecture from that of mammalian species described to date.

Acetylcholinesterase↗
PubMed1990

A new chromogen for use in HRP-tract tracing and double-label immunocytochemistry.

A new chromogen, Indophane Blue (IB) was tested for use in HRP-tract tracing and double-label immunocytochemistry. Although TMB was slightly more sensitive and delineated individual labeled fibers better than IB in tract-tracing experiments, there were two advantages to using IB over TMB. First, the IB reaction could be performed at a pH of 6.0, rather than the pH of 3.3 required for TMB, resulting in much better preservation of tissue. Second, there was no crystalline artifact as has been observed with TMB. In the double-label immunocytochemistry experiments, the combination of diaminobenzidine for the first chromogen and IB as the second, provided excellent contrast.

Animals↗
PubMed1989

Retrograde transneuronal transport of herpes simplex virus in the retina after injection in the superior colliculus, hypothalamus and optic chiasm.

Immunocytochemistry was used to identify infected cells after injection of Herpes simplex virus (HSV) into the superior colliculus, hypothalamus and optic chiasm. Ganglion cells of the retina were labeled in a pattern consistent with known projections to retinorecipient nuclei. Cells of both the inner and outer nuclear layer were labeled. If this represents retrograde transneuronal transport, then HSV may provide an important tool for studying the neuronal circuitry of the retina.

Animals↗
PubMed1989

Retinal projections in quail (Coturnix coturnix).

The trajectory of retinal projections and the location of retinorecipient nuclei in the quail brain was examined after application of horseradish peroxidase (HRP) either to the cut end of the optic nerve or following intraocular injection of HRP. Retinal projections to the hypothalamus, dorsalateral anterior thalamus (rostralateral part, magnocellular part, and lateral part), lateral anterior thalamus, lateroventral geniculate nucleus, lateral geniculate intercalated nuclei (rostral and caudal parts), ventrolateral thalamus, superficial synencephalic nucleus, external nucleus, tectal gray, diffuse pretectal area, pretectal optic area, ectomammillary nucleus, and optic tectum were revealed. Retinal projections observed in quail were compared with results obtained in other avian species and considered in relation to possible anatomic pathways underlying photoperiodism and circadian rhythms.

Animals↗
PubMed1989

Retinohypothalamic projections and the suprachiasmatic nucleus in birds.

Although many investigators have examined retinal projections in birds, there is uncertainty as to the location and identity of a retinorecipient nucleus in the hypothalamus of Aves. A direct retinohypothalamic projection to the medial hypothalamic suprachiasmatic nucleus in mammals is believed to play a role in the entrainment of circadian rhythms. A direct retinohypothalamic projection could subserve a similar function in birds. In the present experiment, horseradish peroxidase, injected intravitreously or applied to the cut optic nerve, consistently labeled a retinorecipient nucleus in the lateral hypothalamus in ringdoves, budgerigars, quails, starlings, and song sparrows, while a significant retinal input to a medial hypothalamic nucleus was absent in these species. These results are interpreted in the light of reports of two retinorecipient nuclei, one in the medial and the other in the lateral hypothalamus, in several classes of vertebrates.

Animals↗
PubMed1989

A double-label pre-embedding immunoperoxidase technique for electron microscopy using diaminobenzidine and tetramethylbenzidine as markers.

Techniques for correlative double-label immunocytochemistry (ICC) at light and electron microscopic (EM) level are useful for determining the neurotransmitter phenotype of inputs onto immunocytochemically identified neurons. Tetramethylbenzidine (TMB) has been used as a chromogen at the EM level for horseradish peroxidase tract tracing. We have found that TMB, in combination with diaminobenzidine (DAB), can be used in a double-label immunocytochemical protocol to examine neuropeptide Y inputs onto luteinizing hormone-releasing hormone cells in the sheep preoptic area. At both light and EM levels, TMB reaction product is visibly distinct from DAB reaction product. The ultrastructural preservation we have been able to obtain with our technique is better than that obtained with techniques that use TMB at a lower pH. Furthermore, this technique allows the demonstration of synaptic contacts between neurochemically identified terminals and cells with different neurotransmitter phenotypes.

3,3'-Diaminobenzidine↗
PubMedDate not supplied

Nuclear transfer technology in mammalian cloning.

The past several years have witnessed remarkable progress in mammalian cloning using nuclear transfer (NT). Until 1997 and the announcement of the successful cloning of sheep from adult mammary gland or fetal fibroblast cells, our working assumption was that cloning by NT could only be accomplished with relatively undifferentiated embryonic cells. Indeed, live offspring were first produced by NT over 15 years ago from totipotent, embryonic blastomeres derived from early cleavage-stage embryos. However, once begun, the progression to somatic cell cloning or NT employing differentiated cells as the source of donor nuclei was meteoric, initially involving differentiated embryonic cell cultures in sheep in 1996 and quickly thereafter, fetal or adult somatic cells in sheep, cow, mouse, goat, and pig. Several recent reviews provide a background for and discussion of these successes. Here we will focus on the potential uses of reproductive cloning along with recent activities in the field and a discussion concerning current interests in human reproductive and therapeutic cloning.

Animal Husbandry↗