Transplanted Neuroblasts Differentiate Appropriately into Projection Neurons with Correct Neurotransmitter and Receptor Phenotype in Neocortex Undergoing Targeted Projection Neuron Degeneration

Abstract

Reconstruction of complex neocortical and other CNS circuitry may be possible via transplantation of appropriate neural precursors, guided by cellular and molecular controls. Although cellular repopulation and complex circuitry repair may make possible new avenues of treatment for degenerative, developmental, or acquired CNS diseases, functional integration may depend critically on specificity of neuronal synaptic integration and appropriate neurotransmitter/receptor phenotype.The current study investigated neurotransmitter and receptor phenotypes of newly incorporated neurons after transplantation in regions of targeted neuronal degeneration of cortical callosal projection neurons (CPNs). Donor neuroblasts were compared to the population of normal endogenous CPNs in their expression of appropriate neurotransmitters (glutamate, aspartate, and GABA) and receptors (kainate-R, AMPA-R, NMDA-R. and GABA-R), and the time course over which this phenotype developed after transplantation.Transplanted immature neuroblasts from embryonic day 17 (E17) primary somatosensory (S1) cortex migrated to cortical layers undergoing degeneration, differentiated to a mature CPN phenotype, and received synaptic input from other neurons. In addition, 23.1 Ϯ 13.6% of the donor-derived neurons extended appropriate long-distance callosal projections to the contralateral S1 cortex. The percentage of donor-derived neurons expressing appropriate neurotransmitters and receptors showed a steady increase with time, reaching numbers equivalent to adult endogenous CPNs by 4-16 weeks after transplantation.These results suggest that previously demonstrated changes in gene expression induced by synchronous apoptotic degeneration of adult CPNs create a cellular and molecular environment that is both permissive and instructive for the specific and appropriate maturation of transplanted neuroblasts. These experiments demonstrate, for the first time, that newly repopulating neurons can undergo directed differentiation with high fidelity of their neurotransmitter and receptor phenotype, toward reconstruction of complex CNS circuitry.

Neurogenesis of corticospinal motor neurons extending spinal projections in adult mice

“…At 8 weeks, no projections by newborn CSMN were observed ( Fig. 4I; n ϭ 5), indicating that extension of such long projections takes longer than 8 weeks, consistent with prior results with transplanted neuroblasts (26,27,34). At 12 and 16 weeks after neuronal recruitment, we observed a subpopulation of newborn BrdUrdϩ neurons that were retrogradely labeled with FG (Fig.…”

“…We induced synchronous apoptotic degeneration of CSMN in 6-week-old mice via chromophore targeting ( Fig. 1) (22,23,26,27). Approximately 10-20% of CSMN underwent apoptosis after successful chromophore targeting.…”

Manipulation of Neural Precursors in situ Induction of Neurogenesis in the Neocortex of Adult Mice

“…In addition, transplanted neurons expressed neurotransmitters and neurotransmitter receptors appropriate to the region of cortex into which they were transplanted. Donor neurons expressed the same complement of neurotransmitters (glutamate, aspartate, and GABA) and receptors (kainate-R, AMPA-R, NMDA-R. and GABA-R) as endogenous cortical projection neurons (Shin et al 2000). Taken together, these results demonstrate that targeted cortex induces immature neurons to differentiate into neurons that closely resemble the neurons that were induced to degenerate.…”

Successful Retrograde Transport of Fluorescent Latex Nanospheres in the Cerebral Cortex of the Macaque Monkey

“…Furthermore, we evaluated the possibility of applying the experimental approach of targeted apoptotic neuronal cell death, which is one of the most common ways in which the nanosphere delivery system has been employed using other animal models [2,3,[19][20][21]. This was done by confirming that craniotomy and laser illumination could be performed on macaque monkeys without causing any non-specific damage.…”

“…This was done by confirming that craniotomy and laser illumination could be performed on macaque monkeys without causing any non-specific damage. Since many reports have suggested the usefulness of the latex nanosphere delivery system (LNDS) for future therapeutic studies [4,10,14,[20][21][22], it makes sense to investigate this theme with primates in order to establish a model for performing appropriate preclinical examinations prior to using the technique on humans.…”