AGING, A PATHOLOGICAL FACTOR IN NEUROLOGICAL INJURY

One of the main reasons for CNS drugs to fail in clinical development is not considering age as a risk factor while studying chronic age-related neurological/neurodegenerative diseases in preclinical studies. We first set out to gain a comprehensive understanding of the impact of age on various aspects (anatomical, immunological, and biochemical) in rodents that play a key role in determining the onset, progression, and evolution of disease severity. With advancing age, the vascular structure and function are compromised which is hypothesized to accelerate cognitive decline. The initial step toward developing novel therapeutics is to characterize the age-related vascular modifications. Utilizing a vessel painting technique, we labelled the surface cortical vessels of young and aged Sprague-Dawley rats and analyzed for classical angiographic features (junctions, lengths, end points, density, etc). We found significant decrease in vascular components while vascular complexity and lacunarity were significantly increased in the aged brain compared to young brain. These age-dependent changes were prominent at the level of right and left middle cerebral artery (MCA) as well as on a global scale. Next, we investigated the changes on the peripheral immune response following lipopolysaccharide (LPS) induced acute systemic inflammation in young and aged Sprague Dawley rats. We observed age-related immunosuppression in the splenic leukocytes indicative of reduced ability of the spleen to retain the immune cells. We also found dysregulated cytokine/chemokine expression in the plasma following LPS stimulation in aged and young animals. Interestingly, we noticed significant increase in circulatory neutrophil population in the aged animals compared to young animals in response to LPS at 24h. Taken together, these studies confirm the presence of age-related modifications in the vasculature as well as immune system suggesting altered response to injury/infection and thus emphasizing the need to utilize age-appropriate models when studying diseases of the elderly. Lastly, we wanted to test the therapeutic effect of a novel agent in case of brain injury model in aged rodents. Previous studies by our lab and others have showed that targeting mitoNEET using NL-1 was neuroprotective following brain injury models. We wanted to investigate if administration of NL-1 could improve functional outcomes following stroke in an aged rodent model of cerebral ischemia reperfusion injury. We found significant decrease in infarct volume and edema index at 24h post stroke. We also saw enhanced survival and reduced behavior deficits. Moreover, we showed improved BBB integrity, reduced oxidative stress and apoptosis at 72h post stroke. Interestingly, PLGA encapsulated NL-1 at 0.25mg/kg (which is 40-fold lesser dose than NL-1 at 10mg/kg) produced better therapeutic effects. Future studies should focus on understanding the mechanism underlying the biology of aging thus enabling the development of novel therapeutic targets for neurological disorders/diseases

Differential Postnatal Expression of Neuronal Maturation Markers in the Dentate Gyrus of Mice and Rats

The dentate gyrus (DG) is a unique structure of the hippocampus that is distinguished by ongoing neurogenesis throughout the lifetime of an organism. The development of the DG, which begins during late gestation and continues during the postnatal period, comprises the structural formation of the DG as well as the establishment of the adult neurogenic niche in the subgranular zone (SGZ). We investigated the time course of postnatal maturation of the DG in male C57BL/6J mice and male Sprague-Dawley rats based on the distribution patterns of the immature neuronal marker doublecortin (DCX) and a marker for mature neurons, calbindin (CB). Our findings demonstrate that the postnatal DG is marked by a substantial maturation with a high number of DCX-positive granule cells (GCs) during the first two postnatal weeks followed by a progression toward more mature patterns and increasing numbers of CB-positive GCs within the subsequent 2 weeks. The most substantial shift in maturation of the GC population took place between P7 and P14 in both mice and rats, when young, immature DCX-positive GCs became confined to the innermost part of the GC layer (GCL), indicative of the formation of the SGZ. These results suggest that the first month of postnatal development represents an important transition phase during which DG neurogenesis and the maturation course of the GC population becomes analogous to the process of adult neurogenesis. Therefore, the postnatal DG could serve as an attractive model for studying a growing and functionally maturing neural network. Direct comparisons between mice and rats revealed that the transition from immature DCX-positive to mature CB-positive GCs occurs more rapidly in the rat by approximately 4–6 days. The remarkable species difference in the speed of maturation on the GC population level may have important implications for developmental and neurogenesis research in different rodent species and strains

Differential postnatal expression of neuronal maturation markers in the dentate gyrus of mice and rats

The dentate gyrus (DG) is a unique structure of the hippocampus that is distinguished by ongoing neurogenesis throughout the lifetime of an organism. The development of the DG, which begins during late gestation and continues during the postnatal period, comprises the structural formation of the DG as well as the establishment of the adult neurogenic niche in the subgranular zone (SGZ). We investigated the time course of postnatal maturation of the DG in male C57BL/6J mice and male Sprague-Dawley rats based on the distribution patterns of the immature neuronal marker doublecortin (DCX) and a marker for mature neurons, calbindin (CB). Our findings demonstrate that the postnatal DG is marked by a substantial maturation with a high number of DCX-positive granule cells (GCs) during the first two postnatal weeks followed by a progression toward more mature patterns and increasing numbers of CB-positive GCs within the subsequent 2 weeks. The most substantial shift in maturation of the GC population took place between P7 and P14 in both mice and rats, when young, immature DCX-positive GCs became confined to the innermost part of the GC layer (GCL), indicative of the formation of the SGZ. These results suggest that the first month of postnatal development represents an important transition phase during which DG neurogenesis and the maturation course of the GC population becomes analogous to the process of adult neurogenesis. Therefore, the postnatal DG could serve as an attractive model for studying a growing and functionally maturing neural network. Direct comparisons between mice and rats revealed that the transition from immature DCX-positive to mature CB-positive GCs occurs more rapidly in the rat by approximately 4–6 days. The remarkable species difference in the speed of maturation on the GC population level may have important implications for developmental and neurogenesis research in different rodent species and strains