Axonal domains within shared touch domes in the rat: a comparison of their fate during conditions favoring collateral sprouting and following axonal regeneration

Low-threshold mechanosensory nerves in the adult rat differ both from their counterparts in lower vertebrates and from high-threshold nociceptive nerves in mammals in that they appear not to undergo collateral sprouting into adjacent denervated skin, although they will clearly regenerate into it after they are damaged. We have now studied the growth capabilities of the low-threshold nerves supplying touch domes, the visible mechanosensory structures scattered throughout the hairy skin. Touch domes in the rat are often multiply innervated. A serendipitous observation on such domes allowed us to investigate the possibility that a functional collateral sprouting of their nerves can indeed occur, but only to a spatially very restricted extent, e.g., within the confines of a partially denervated dome. We used a "prodder" with a tip diameter of 16 micron to examine the mechanosensory profile across single domes that were preselected as being supplied by only two axons, one running in each of two adjacent dorsal cutaneous nerves (DCNs). Simultaneous recordings were made of the afferent discharges evoked in these nerves when the prodder was applied at about 17 or more locations on a selected dome; the spatial resolution was better than 55 micron. We found that within such a shared dome, one axon can supply a discrete territory (its "domain"), which may or may not overlap with the corresponding domain of the other axon. In a preliminary electron microscopic study, we found no evidence for a sharing of single Merkel cells, which are the specialized sensory cells in touch domes, even in the regions of a shared dome where two domains overlapped; each innervated Merkel cell appeared to be contacted by a single nerve ending, implying that in a shared dome each axon probably supplies an exclusive subpopulation of the Merkel cells. We tested for functional collateral sprouting by eliminating one nerve to a shared dome, and at a selected time thereafter mapping the domain of the remaining axon to see whether it had enlarged. The result was the same whether the two domains initially had a region of overlap or not; no expansion of the surviving domain occurred over postoperative periods up to 4 months (an expansion of the domain by 55 micron would have been detected). Thus functional collateral sprouting had failed to occur.(ABSTRACT TRUNCATED AT 400 WORDS)     

New view of the organization of the pulvinar nucleus in Tupaia as revealed by tectopulvinar and pulvinar-cortical projections

The projections of the superficial layers of the superior colliculus to the pulvinar nucleus in Tupaia were reexamined by injecting WGA-HRP into the tectum. The main result was finding two different patterns of terminations in the pulvinar nucleus: a zone remote from the lateral geniculate nucleus, which occupies the dorsomedial and caudal poles of the pulvinar nucleus, was almost entirely filled with terminals in every case irrespective of the location of the injection site; and a second division of the pulvinar nucleus, adjacent to the lateral geniculate nucleus, contained irregular patches--much more densely populated--and the distribution of patches varied from case to case. We call the first projection "diffuse" and the patchy projection "specific." Next we injected several divisions of the extrastriate visual cortex to find the cortical target of each pathway. The diffuse path terminates in the ventral temporal area (Tv). The specific path terminates in the dorsal temporal area (Td) and area 18. We speculated about the significance of the two pathways: the specific path may be responsible for the preservation of vision after removal of the striate cortex; the diffuse path may have an important place in the evolution of the visual areas of the temporal and occipital lobe. We argued that the target of the diffuse path is in a position to relate limbic and visual impulses and relay the product of such integration to the other visual areas, striate as well as extrastriate cortex.     

Cortical asymmetry--a preliminary study: neurons-glia, female-male

Previous studies on human cortical area 39 suggested that neuron:glial ratios differed between the sexes. These findings were the inspiration for the present investigation which dealt with neuronal and glial counts in area 39 in the male and female rat cerebral cortex. Transverse, celloidin or frozen sections, were cut from male and female brains (respectively) from 90-day-old Long-Evans rats. Neurons and glia were counted on enlarged photographs of stained sections, including area 39, with 35-mm Kodak Panatomic-X film using a Zeiss photomicroscope (X400). Five-by-three-inch prints were taped together in sequence to yield a 640X enlarged "montage" of area 39. Five cell types were differentiated with reference to a standard: neurons, astrocytes, oligodendrocytes, "dark astrocytes," and unidentified glia. The data were analyzed with a two-way analysis of variance (ANOVA: five cell types by two hemispheres). Student's t test and a paired t test were used when appropriate. The neuron:glial ratios in the male rats were consistently higher than those in the females in both hemispheres. The male right side had 12% (P less than 0.05) more neurons than the left; the female had 13% (P less than 0.05) more neurons on the left than the right. Similar, but not identical, asymmetrical patterns were seen with the glial cells.     

Sympathetic nerves in adult rats regenerate normally and restore pilomotor function during an anti-NGF treatment that prevents their collateral sprouting.

We have used anti-nerve growth factor (anti-NGF) [corrected] administration to study the NGF dependency of the reinnervation of denervated skin by sympathetic nerves in the adult rat. Sympathetic pilomotor fields were revealed by electrical stimulation of selected dorsal cutaneous nerves; the affected skin rapidly assumed a "gooseflesh" appearance, sharply demarcated from surrounding unstimulated skin. Examined 2-5 days after section of neighboring nerves, the "isolated" pilomotor field of the spared nerve was found to be coextensive with an area of amine-fluorescent fibers that were associated with pilomotor muscles and blood vessels. After its isolation, a pilomotor field begins to expand into the surrounding deprived territory, reaching a maximum size at approximately 40 days. Fluorescence studies confirmed that new sympathetic fiber growth had occurred into the expanded regions of such fields. Daily injections of polyclonal anti-NGF serum completely prevented these pilomotor field expansions. Following termination of the anti-NGF treatment, expansion proceeded normally. Finally, if the onset of anti-NGF treatment was delayed until pilomotor field expansion had already commenced, further expansion was halted. Regeneration of sympathetic fibers was evoked by crushing a selected nerve. Recovery of pilomotor function in the totally denervated skin was first detected at about 20 days postcrush, and the field progressively enlarged over the next 40 days. Although the imposed NGF deprivation is known to cause a demonstrable shrinkage, and presumably atrophy, of sympathetic ganglia, the anti-NGF treatment appeared to impair neither the restoration of a pilomotor field after nerve crush, nor its continued expansion into skin regions well beyond that originally supplied by the nerve, i.e., into territory whose invasion by collateral sprouts would have been totally prevented by the treatment. During such NGF deprivation, fluorescent regenerating fibers were visualized in the nerve trunk. We conclude that even though the regenerating and collaterally sprouting sympathetic fibers probably utilise the same degenerating dermal pathways to reach and functionally reinnervate the same denervated targets, only the collateral sprouting of the uninjured axons is dependent upon endogenous NGF. These findings extend the results described earlier for nociceptive fibers, and suggest that the contrasting dependencies upon growth factors of sprouting and regeneration might apply throughout the adult nervous system.     

Effect of norgestrel on development of mouse pre-embryos

The effect of synthetic progestins found in oral contraceptives has potential implications for developing embryos in women who receive oral contraceptives during early pregnancy. We assessed the effect of the progestin norgestrel on the developing pre-embryo. B3C6F1 mice were given 5 IU PMSG followed by 5 IU hCG 48h later. Studies were performed on pre-embryos recovered and pooled at both 24h (Group A) and 48h (Group B) post hCG. At each time period, they were randomly assigned to control or norgestrel (4.0 ng/ml) treatment. In a third study, pre-embryos collected 24h post hCG were cultured in the absence or presence of 8.0, 80.0, or 800 ng/ml norgestrel. Cultures were performed in Ham's F-10 media with 10% fetal calf serum at 37 degrees C in an atmosphere of 5% CO2, 5% O2 and 90% N2 with 15-30 embryos per 1 ml of culture fluid. At 24h, 48h and 72h post recovery, cultures were viewed, the appearance of embryos noted, and number of blastomeres recorded. Compared to control groups, analysis demonstrated no significant difference in the rate of development of control and norgestrel pre-embryos in any group at any time period (24h, 48h, or 72h post recovery). We conclude that norgestrel at the dose tested has no acute adverse morphological effects on development of mouse pre-embryos. This observation has potential clinical implications with regard to inadvertent use of norgestrel-containing oral contraceptives during early days of pregnancy, as well as consideration of the mechanism of action of norgestrel-containing "morning after" pills.     

PJA-BP expression and TCR delta deletion during human T cell differentiation

Recombination of deltaRec to psiJalpha will delete the TCR delta gene, which is thought to play an important role in the bifurcation of the TCR alphabeta versus TCR gammadelta differentiation lineages. We recently detected a DNA-binding protein in human thymocytes, the so- called PJA-BP, which recognizes the psiJalpha gene segment and might be one of the factors involved in the regulation of preferential deltaRec- psiJalpha rearrangements. We now investigate PJA-BP expression and its correlation with TCR delta gene deletion in thymocytes. Our electrophoretic mobility shift assay experiments showed that the PJA-BP is evolutionary conserved in human, murine and simian thymocytes. Using a large series of human hematopoietic malignancies (n = 30), we conclude that PJA-BP expression is thymocyte specific and seems to be restricted to thymocytes committed to the TCR alphabeta lineage. Analysis of seven well-defined human thymocyte subpopulations showed that preferential deltaRec-psiJalpha rearrangements as well as PJA-BP expression can be detected from the immature CD34-/CD1+/CD3- /CD4+/CD8alpha+beta- thymocyte differentiation stage onwards. These experiments indicate that expression of PJA-BP in human thymocytes starts simultaneously with preferential deltaRec-psiJalpha rearrangements, which supports our hypothesis that PJA-BP is one of the factors involved in the preferential recombination of deltaRec to psiJalpha.      

Intranasal administration of a beta adrenergic amine: an alternative to metered-dose inhalers.

In anesthetized, artificially ventilated guinea pigs, intranasal and intravenous administration of albuterol produced the same maximum degree of protection against bronchoconstriction induced by bilateral electrical stimulation of the cervical vagal nerves. Intranasal albuterol showed a slower onset of action than intravenous albuterol and exhibited equivalent cardiovascular side effects for the same level of bronchoprotection. Accordingly, intranasal albuterol may represent an alternative to metered-dose inhalation for prophylaxis and treatment of bronchoconstriction in humans.     

Molecular genetic analysis of autosomal dominant cerebellar ataxia with retinal degeneration (ADCA type II) caused by CAG triplet repeat expansion

Autosomal dominant cerebellar ataxia with retinal degeneration (ADCAII) was previously mapped by linkage analysis studies to chromosome 3p12- p21.1 (SCA7). Positional cloning efforts have recently identified a novel gene, SCA7 , containing a translated CAG repeat, expanded in SCA7 patients. We cloned the SCA7 gene from a yeast artificial chromosome (YAC) clone contig spanning the SCA7 candidate region. Using a combination of genomic sequencing and cosmid-based exon trapping, two expressed sequence tags were identified. Sequencing of the corresponding cDNA clones and RT-PCR analysis identified the full- length SCA7 cDNA. Together, our sequence data defined the intron/exon boundaries of the first two coding exons of the SCA7 gene, with the first exon containing the expanded CAG repeat. Further, sequence comparison with the published SCA7 cDNA identified one additional putative exon in the 5'-UTR region of the SCA7 gene. The SCA7 gene was mapped on the YAC contig in the 2.5 cM interval between D3S1600 and D3S1287. In one extended Belgian SCA7 pedigree the expanded alleles ranged from 38 to at least 55 repeats with allele lengths being inversely correlated with onset age of ADCAII symptoms. The SCA7 repeats increased in length in successive generations. Normal alleles had from four to 18 repeats, with 10 repeats being the most common allele.