Howard O. Nornes

Neurogenesis in spinal cord of mouse: an autoradiographic analysis.

An autoradiographic analysis of the time and sites of origin, and the migration and settling patterns of neurons was made in the spinal cord of the mouse. The neurons originated on days 10--14 of gestation with temporal gradients along the ventrodorsal and rostrocaudal axes. The motor neurons originated on days 10 and 11 of gestation; the neurons in the intermediate gray region originated on days 11--14 of gestation; the neurons of the head of the dorsal horn originated on days 12--14 of gestation. The neurons that originated on days 10 and 11 originated and migrated primarily from the basal plate, and they settled in the adjacent regions of the intermediate zone; those neurons formed on days 12--14 originated and migrated primarily from the alar plate, and it was concluded that these neuroblasts similarly settled in the adjacent regions of the intermediate zone. Extraventricular proliferation, which presumably signaled the initial stages of gliogenesis, was first observed on day 12 of gestation. This study supports the classical idea of the mosaic pattern of neurogenesis in the embryonic spinal cord.

Reinnervation of the denervated adult spinal cord of rats by intraspinal transplants of embryonic brain stem neurons

SummaryPrevious studies have revealed a remarkable capacity of intracerebral grafts of embryonic brain tissue to establish extensive axonal connections with denervated areas in the brains of adult rats. In the present study we have explored the possibilities of using grafts in the spinal cord to substitute for the loss of noradrenergic brain-stem inputs to the severed spinal cord. Intraspinal grafts of embryonic pontine noradrenergic neurons were made into the lower thoracic region of adult rats. Three different surgical techniques were tested: (i) grafting to a small central cavity in the spinal-cord grey matter; (ii) grafting to a small subpial cavity involving removal of the dorsolateral third of the spinal-cord matter; (iii) grafting to the gap between the rostral and caudal stumps of the spinal cord after a nearly complete subpial transection. The results indicate that direct contact with the vessel-rich pia is essential for good survival of the grafts. Provided that the pia was left intact, the scarring around the grafts was minimal and the grafts fused well with both the grey and white matter of the cord. In the subpially transected cord, a brain-stem graft taken from a young embryonic donor fused well with both the rostral and the caudal stumps of the severed cord and thus restored tissue continuity across the gap.Large numbers of catecholamine (CA)-containing and non-monoaminergic cells were present in the transplants after 3–6 months. CA fluorescence histochemistry in combination with injections of fluorescent retrograde tracers revealed that both noradrenergic and non-monoaminergic neurons in the grafts had grown to reinnervate large segments of the host spinal cord. In those cases where the transplant had fused well with the cord, abundant CA-fluorescent axons could be traced across the graft-cord junction. They course along the grey and white matter of the host cord to reestablish a new CA terminal plexus in the grey matter as far as 12 mm from the graft.

The cells of origin of the commissural afferents to the area dentata in the mouse.

The hippocampal commissural projection to the area dentata of the mouse was studied using the retrograde horseradish peroxidase (HRP) technique. Small volumes of HRP injected into the molecular layer of the fascia dentata or various subareas of regio inferior of the hippocampus (fields CA3a-c) resulted inlabeled perikarya in the contralateral hippocampus and area dentata. The commissural projection to the fascia dentata was observed to originate exclusively from cells within the hilus fasciae dentatae (CA4) of the contralateral area dentata. There was evidence of a considerable spread of commissural innervation along the septotemporal axis preferentially in the septal direction, confirming earlier observations. In contrast to the septotemporal spread, a sharp homotopic spatial organization was found in the mediolateral direction. For example, injections into the lateral portion of field CA3 (CA3a) resulted in HRP-positive cell bodies only in the contralateral field CA3a. When injections were made which apparently labeled all of the commissural fibers, the HRP reaction product was found in neurons both in the entire regio inferior and as far as the innermost point of the hilus fasciae dentatae; the majority of labeled cells were located in hippocampal subfield CA3c. No labeled cells were observed beyond the tip of the mossy fibers in regio superior.

Transplants of embryonic brainstem containing the locus coeruleus into spinal cord enhance the hindlimb flexion reflex in adult rats

Cell suspensions of embryonic brainstem containing the locus coeruleus were injected intervertebrally into the lumbar spinal cord of adult rats whose descending catecholamine (CA) fibers had been lesioned with intracisternal injection of 6-hydroxydopamine. Up to 1100 CA cells were found 2 and 4 months later, and these cells grew processes which produced histologically detectable reinnervation of the lumbar gray matter on the injected side of the cord. To assess the functional activity of the transplanted CA cells, the force of the hindlimb flexion reflex was measured in acute spinal rats. This reflex has been shown previously to be strongly enhanced by catecholamines. The flexion reflexes were significantly stronger in the transplanted rats than in the controls. Further, the flexion reflexes were significantly reduced by phenoxybenzamine, an alpha-adrenergic blocker, in the transplanted rats while the reflexes of controls were not significantly changed. These results demonstrate that cell suspension transplants of embryonic brainstem containing the locus coeruleus into the adult rat spinal cord survive, grow reinnervating catecholamine processes, and can affect the functional activity of the spinal cord.

Cyclin E is expressed in neurons and forms complexes with cdk5.

&NA; Expression of cyclin dependent kinase cdk5 and its regulator p35 has been shown in the cytoplasm of adult neurons. Here we demonstrate that another potential regulator of cdk5, cyclin E, is expressed in the nervous system and forms complexes with cdk5. Western blot analyses identifies expression of two forms of cyclin E in the mouse nervous system with the 56 kDa form mainly expressed in neurons and 51 kDa form expressed in astrocytes and oligodendrocytes.

Time of Origin of the Neurons in the Caudal Brain Stem of Rat

This study was designed to determine the time of origin of neurons in the caudal brain stem of rat. A single injection of [3H]-thymidine was given to a pregnant animal for each of the days

Transplantation Strategies in Spinal Cord Regeneration

Transplantation models in the brain have proven successful under conditions in which transplants serve as a “bridge” for the regeneration of axons across a site of injury, or as “release” or “driving” units to replace missing inputs to a particular target area.1–8 Similar models have been applied to the mammalian spinal cord including: (1) intraspinal transplants to form a bridge for the regeneration of spinal cord axons, (2) extraspinal transplants with only the end or ends of the transplants inserted into the cord to bypass the region of injury, and (3) intraspinal neural implants to replace missing supraspinal inputs. These models demonstrate that neurons of the spinal cord possess the ability to regenerate axons several millimeters into both intrinsic and extrinsic transplants; however, the growth of these axons into the tissue of the host spinal cord has been limited. By contrast, embryonic CNS neurons transplanted into the adult spinal cord, possess the ability to grow axons that penetrate several millimeters into spinal cord tissue. This review provides an overview of the attempts to promote regeneration of spinal cord connections by using various transplantation paradigms.

Helix-loop-helix transcription factors regulate Id2 gene promoter activity

Id‐like helix‐loop‐helix (HLH) transcription factors are involved in the regulation of proliferation and differentiation of several cell types. We isolated 5′ regulatory region of mouse Id2 gene and demonstrated that it contains several E‐box clusters. These E‐boxes mediate stimulatory effects of basic‐HLH (bHLH) transcription factors ME1, ME2, and NSCL1 on Id2 promoter activity. Co‐expression of Id2 blocks the stimulatory effect of bHLH transcription factors which suggests the presence of feedback loops in Id2 transcriptional regulation. Overexpression of NSCL1 in F9 cells blocks the downregulation of Id2 gene expression during retinoic acid induced differentiation. Our data demonstrate that bHLH transcription factors regulate Id2 gene expression.

A neurotransmitter specific functional recovery mediated by fetal implants in the lesioned spinal cord of the rat

In the electrophysiologic test of the hindlimb withdrawal reflex where the long latency component is found to be dependent on noradrenaline (NA), implants of fetal NA tissue in lesioned animals result in a recovery of NA dependent function proportional to the number of catecholamine fluorescent cells in the implants.

All-trans retinoic acid affects the expression of orphan receptors COUP-TF I and COUP-TF II in the developing neural tube

The effect of all-trans retinoic acid (RA) on chicken ovalbumin upstream promoter-transcription factor (COUP-TF) I and COUP-TF II expression in the developing cervical spinal cord and telencephalon was examined using embryonic day 11 and 13 mice. All-trans RA treatment results in changes in expression of COUP-TF I and COUP-TF II genes in the spinal cord and telencephalon. COUP-TF I mRNA levels were reduced in the spinal cord ventricular zone (VZ) after treatment, whereas in the telencephalon, mRNA levels were unaffected in the VZ and increased in the intermediate zone (IZ). COUP-TF II mRNA levels were increased in the spinal cord VZ after treatment, while in the telencephalon, IZ mRNA levels were decreased in the E11 embryos and increased in E13 embryos.