Optimization of Experimental Conditions to Characterize Perineuronal Nets in the Human Cerebellum

Abstract

During childhood and adolescence, the brain is highly responsive to external stimuli compared to adulthood. Perineuronal nets (PNNs), play a crucial role during this period by reducing neuroplasticity. These mesh-like structures protect and fortify neural connections between cells. Child abuse includes physical, emotional, and sexual abuse and/or neglect1. It is consistently associated with negative mental and physical health outcomes, underscoring the importance of identifying risk and resilience factors for effective prevention of such outcomes. Our laboratory focuses on understanding the cellular and molecular neuroanatomy of major depression and the lasting impact of child abuse (CA) on the brain. However, the impact of CA on PNNs remains relatively unexplored. How does CA influence the brain, potentially contributing to negative outcomes in the future? Samples from post-mortem human brain cerebellum were dissected and then used to perform RNAscope experiments to label glutamatergic, GABAergic, and parvalbumin-positive cells, following a brief IF protocol using Wisteria Floribunda Lectin (WFL) to visualize PNNs. The RNAscope protocol was successfully optimized by the addition of normal donkey serum (NDS), manipulation of incubation time, and WFL concentration. PVALB+ mRNA expression was positively identified in Purkinje cells, molecular layer interneurons, and deep cerebellar nucleus (DCN) neurons. SLC17A7+ mRNA expression was evident in granule cells and excitatory projection DCN neurons. GAD1+ mRNA expression was detected in Purkinje cells and inhibitory DCN neurons. These results provide an experimental protocol for future studies investigating the role of PNNs in the human cerebellum. We propose that CA alters the recruitment of PNNs, influencing circuitry and potentially increasing susceptibility to various mental illnesses, including major depressive disorder (MDD). MDD, also called clinical depression, causes a persistent feeling of sadness and loss of interest. This study aims to optimize fluorescent in situ hybridization (FISH, RNAscope) and immunofluorescence (IF) markers for the localization and phenotyping of PNN-enwrapped neurons in the human cerebellum. This article describes problems we encountered when running experiments and ways to optimize them. As this work is preliminary, it will help develop future protocols for exploring the effects of depression on PNNs and the phenotype of the cells they encircle. Comparing depressed individuals with and without a history of CA with neurologically and psychiatrically healthy controls will allow us to determine whether a history of CA impacts the distribution and density of PNNs.