Intraretrosplenial cortical grafts of fetal cholinergic neurons and the restoration of spatial memory function

Cell Therapy From Bench to Bedside Translation in CNS Neurorestoratology Era

Recent advances in cell biology, neural injury and repair, and the progress towards development of neurorestorative interventions are the basis for increased optimism. Based on the complexity of the processes of demyelination and remyelination, degeneration and regeneration, damage and repair, functional loss and recovery, it would be expected that effective therapeutic approaches will require a combination of strategies encompassing neuroplasticity, immunomodulation, neuroprotection, neurorepair, neuroreplacement, and neuromodulation. Cell-based restorative treatment has become a new trend, and increasing data worldwide have strongly proven that it has a pivotal therapeutic value in CNS disease. Moreover, functional neurorestoration has been achieved to a certain extent in the CNS clinically. Up to now, the cells successfully used in preclinical experiments and/or clinical trial/treatment include fetal/embryonic brain and spinal cord tissue, stem cells (embryonic stem cells, neural stem/progenitor cells, hematopoietic stem cells, adipose-derived adult stem/precursor cells, skin-derived precursor, induced pluripotent stem cells), glial cells (Schwann cells, oligodendrocyte, olfactory ensheathing cells, astrocytes, microglia, tanycytes), neuronal cells (various phenotypic neurons and Purkinje cells), mesenchymal stromal cells originating from bone marrow, umbilical cord, and umbilical cord blood, epithelial cells derived from the layer of retina and amnion, menstrual blood-derived stem cells, Sertoli cells, and active macrophages, etc. Proof-of-concept indicates that we have now entered a new era in neurorestoratology.

Acetylcholine efflux from retrosplenial areas and hippocampal sectors during maze exploration

Both the retrosplenial cortex (RSC) and the hippocampus are important for spatial learning across species. Although hippocampal acetylcholine (ACh) release has been associated with learning on a number of spatial tasks, relatively little is understood about the functional role of ACh release in the RSC. In the present study, spatial exploration was assessed in rats using a plus maze spontaneous alternation task. ACh efflux was assessed simultaneously in the hippocampus and two sub-regions of the RSC (areas 29ab and 30) before, during and after maze exploration. Results demonstrated that there was a significant rise in ACh efflux in RSC area 29ab and the hippocampus during maze traversal. The rise in ACh efflux across these two regions was correlated. There were no significant behaviorally driven changes in ACh efflux in RSC area 30. While both the hippocampal sectors and area 29ab displayed increases in ACh efflux during maze exploration, the percent ACh rise in area 29ab was higher than that observed in the hippocampus and persisted into the post-baseline period. Joint efflux analyses demonstrated a key functional role for ACh release in area 29ab during spatial processing.

A reaffirmation of the retrosplenial contribution to rodent navigation: reviewing the influences of lesion, strain, and task

Retrosplenial cortex (RS) is situated both anatomically and functionally between neocortical and limbic structures involved in spatial navigation. Initial anatomical, electrophysiological and behavioural evidence in both humans and rodents strongly suggested a role for RS in spatial navigation as well. Later studies using more selective cytotoxic lesions in rodents, however, cast doubt on earlier RS studies by failing to find spatial deficits following RS lesions. Contrasting reports from behavioural results on spatial tasks following RS damage have continued to be reported during the past decade. That RS does indeed contribute spatial behaviour even in rodents has been recently reaffirmed. The ambiguity surrounding RS is shown to result from differences in the choice of spatial tasks and rat strains between studies that find RS deficits and those that do not. The reconciliation of behavioural results following RS lesions strengthens the view that RS forms a part of the neural circuitry that underlies spatial navigation.

Testing the importance of the retrosplenial navigation system: lesion size but not strain matters: a reply to Harker and Whishaw

In their review on the retrosplenial cortex Harker and Whishaw [Neurosci Biobehav Rev, 2004] claim that there is continued disagreement over the importance of this region for navigation. They argue that discrepancies in the published effects of retrosplenial lesions reflect two principal variables, choice of rat strain and choice of spatial task. In this reply, evidence is provided showing that Harker and Whishaw [Neurosci Biobehav Rev, 2004] have created a misleading impression and, in fact, there is a clear consensus that the rat retrosplenial cortex is necessary for navigation. Likewise, there is no dispute that the effects of retrosplenial lesions will differ for different tests of spatial learning. While Harker and Whishaw [Neurosci Biobehav Rev, 2004] also conclude that choice of rat strain has a critical impact on whether a lesion-induced deficit is found, a comprehensive review of the published data shows no systematic strain difference. There is, however, growing evidence that when interpreting the effects of retrosplenial lesions, account should be given of the lesion method and its interaction with lesion size.

Developmental regulation of pituitary adenylate cyclase-activating polypeptide and PAC(1) receptor mRNA expression in the rat central nervous system

As the brain develops, a homogeneous population of mitotically active progenitors generates the molecularly heterogeneous post-mitotic cells of the mature brain. The balance between cell division, growth arrest and differentiation of these progenitors undoubtedly requires the activation of a vast array of genes. Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the vasoactive intestinal polypeptide (VIP)/secretin/glucagon family. Within the nervous system, PACAP has been shown to stimulate neurite outgrowth, regulate neurotransmitter production and neuronal survival. These diverse biological actions are mediated through interaction with two types of receptors, a PACAP-selective receptor (PAC(1)-R) and receptors which interact almost equally with both VIP and PACAP. Since several lines of evidence suggest that PACAP acts as a neurotrophic factor, we sought to characterize PACAP and PAC(1)-R expression in the developing rat nervous system. The PAC(1)-R is expressed at very high levels in ventricular zones throughout the neuraxis. In addition to the embryonic enrichment in proliferative zones, PAC(1)-R expression is maintained in areas of neurogenesis in the adult central nervous system (CNS), namely, the subventricular zone of the olfactory bulb and hippocampal dentate gyrus. In contrast, PACAP is expressed primarily in the post-mitotic parenchyma. This temporal regulation and cellular distribution suggests that PACAP, through its interaction with the PAC(1)-R, may play a role in mammalian neurogenesis.

Intra-retrosplenial cortical grafts of cholinergic neurons: functional incorporation and restoration of high affinity choline uptake

Fetal septal neurons transplanted into the deafferented retrosplenial cortex (RSC) of rats have been shown to reinnervate the host brain and ameliorate spatial memory deficits. In the present study we examined the effects of implanting cholinergic neurons on high affinity choline uptake (HACU) in the denervated RSC and the correlational relationship between this cholinergic parameter and the level of behavioral recovery. Three groups of animals were used: 1) normal control rats (NC), 2) rats with lesions of the fornix and cingulate pathways (FX), and 3) lesioned rats with fetal septal grafts in the RSC (RSCsep-TPL). We found that intra-RSC septal grafts produced significant increases in HACU, and that recovery of HACU was significantly correlated with the improvements in the performance of spatial reference memory, spatial navigation, and spatial working memory tasks. We have also investigated the ability of the host brain to modulate the activity of the implanted neurons. In particular we evaluated the effect of the animals' performance in a 6-arm radial maze task on high affinity choline uptake (HACU). Animals in each of the NC, FX, and RSCsep-TPL groups were randomly assigned one of the following subgroups: 1) rats that performed the maze task before the determination of HACU (BEH), or 2) rats that did not perform the maze task before the determination of HACU (NON-BEH). Significant increases were observed in the NC and RSCsep-TPL groups, but not in the FX animals, indicating that fetal septal grafts in the RSC can become functionally incorporated with the host neural circuitry, and that the activity of the implanted cholinergic neurons can be modulated by the host brain.