Effects of environmental enrichment on blood vessels in the optic tract of malnourished rats: A morphological and morphometric analysis

Abstract

Objectives: This study aimed to compare the effects of environmental enrichment in nourished (on a diet containing 16% protein) and malnourished (on a diet containing 6% protein) rats during the critical period of brain development, specifically focusing on the optic nerve.

Methods: By means of morphologic and morphometric assessment of the optic nerve, we analyzed the changes caused by diet and stimulation (environmental enrichment) on postnatal day 35, a time point ideal for such morphological analysis since developmental processes are considered complete at this age.

Results: Malnourished animals presented low body and brain weights and high body-to-brain weight ratio compared to well-nourished rats. Furthermore, malnourished animals showed morphological changes in the optic nerve such as edema and vacuolization characterized by increased interstitial space. The malnourished-stimulated group presented lesions characteristic of early protein malnutrition but were milder than lesions exhibited by malnourished-non-stimulated group. The morphometric analysis revealed no difference in glial cell density between groups, but there was significantly higher blood vessel density in the stimulated rats, independent of their nutritional condition.

Discussion: Our data indicate that protein malnutrition imposed during the critical period of brain development alters the cytoarchitecture of the optic nerve. In addition, we affirm that a 1-hour exposure to an enriched environment everyday was sufficient for tissue preservation in rats maintained on a low-protein diet. This protective effect might be related to angiogenesis, as confirmed by the increased vascular density observed in morphometric analyses.

Keywords:

• Environmental enrichment
• Malnutrition
• Optic nerve
• Glial cells
• Blood vessels
• Angiogenesis
• Protein deficiency
• Cytoarchitecture

Acknowledgements

We would like to thank Mr Rodrigo Focosi Mazzei for animal care assistance, Ms Izilda Violante and Mr Antonio Renato Meirelles for assistance with tissue processing and image digitalization, respectively. Finally, we thank Dr Amilton Antunes Barreira for permitting us to use the ‘Laboratory of Experimental and Applied Neurology’ for image acquisition. This work was supported by the Fundação de Apoio ao Ensino à Pesquisa e Assistência do Hospital das Clínicas da Faculdade de Medicina de Ribeirão Preto (FAEPA) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES).