Liquid diets reduce cell proliferation but not neurogenesis in the adult rat hippocampus

Abstract

Neurogenesis continues to occur in restricted regions of the brain throughout adulthood and can be modulated by dietary factors. Liquid or "soft" diets are commonly used for the administration of drugs in experimental models of disease, making it critical to determine whether dietary composition itself can affect neurogenesis. In this study Sprague-Dawley rats were fed either a liquid or a solid diet of identical composition from weaning until young adulthood. No differences in neuronal differentiation and survival of newly born cells were observed between rats that were fed a liquid diet and those that received a solid diet. However, a significant reduction in hippocampal cell proliferation was observed in the liquid diet-fed group, as assessed by the expression of two endogenous proliferation markers, Ki67 and proliferating cell nuclear antigen (PCNA). The method of feeding did not alter the basal function of the hypothalamic-pituitary-adrenal (HPA) axis in these animals, as no changes in circulating levels of corticosterone (CORT) were detected between liquid and solid diet-fed groups. There was also a significant reduction in cellular proliferation in the hypothalamus of liquid diet-fed rats, a brain region known to be involved in feeding-related behaviors. These findings indicate that liquid diets themselves can directly impact rates of cellular proliferation, but this does not seem to impact levels of overall neurogenesis in the adult brain.

Keywords: 3,3′-diaminobenzidine; 5-bromo-2′-deoxyuridine; ANOVA; BDNF; BrdU; CORT; DAB; DCX; DG; ELISA; GCL; HPA; IgG; NeuN; NeuroD; PCNA; PFA; PND; PVZ; SGZ; SVZ; TBS; Tris-buffered saline; adult neurogenesis; analysis of variance; brain-derived neurotrophic factor; cell proliferation; corticosterone; dentate gyrus; doublecortin; enzyme-linked immunosorbent assay; granule cell layer; hypothalamic–pituitary–adrenal; hypothalamus; immunoglobulin G; liquid diet; mastication; neurogenic differentiation protein; neuronal nuclei; paraformaldehyde; periventricular zone; postnatal day; proliferating cell nuclear antigen; subgranular zone; subventricular zone.