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Differential vulnerability of the rat retina, suprachiasmatic nucleus and intergeniculate leaflet to malnutrition
M C R Vilela1, J E F Mendonça, H Bittencourt
1Departamento de Fisiologia e Farmacologia, Centro de Ciências Biológicas, Cidade Universitária 50670901 Recife, PE, Brazil.
Insights
Early malnutrition subtly impacts the rat circadian timing system, affecting the retina and suprachiasmatic nuclei (SCN) but not retino- or geniculohypothalamic pathways.
Area of Science:
- Neuroscience
- Chronobiology
- Developmental Biology
Background:
- Early life malnutrition is a global health concern.
- Its impact on the development of the circadian timing system is not fully understood.
- The suprachiasmatic nuclei (SCN) is the master circadian clock, receiving input from the retina.
Purpose of the Study:
- To investigate the effects of early malnutrition on key structures of the rat circadian timing system.
- To assess the development of the retina, SCN, and associated neural pathways under conditions of maternal dietary deficiency.
Main Methods:
- Rats were exposed to a multideficient diet either during gestation (GLA group) or lactation (LA group).
- Histological analyses (Nissl staining, immunohistochemistry) and tracer injections were used to examine retinal and SCN morphology and connectivity.
- Quantitative analyses included cell counts, morphometry, and densitometry.
Main Results:
- Malnourished rats exhibited reduced retinal surface area and altered retinal ganglion cell distribution.
- SCN dimensions were affected in both GLA and LA groups at one and two months postnatally.
- The retinal input to the SCN was altered in the GLA group, but the neuropeptide Y (NPY)-containing geniculohypothalamic tract remained unaffected.
Conclusions:
- Early malnutrition induces subtle, differential vulnerabilities in the developing circadian timing system structures.
- The observed changes do not fully explain previously documented alterations in circadian rhythmicity in malnourished rats.
- Developmental integrity of retino- and geniculohypothalamic projections to the SCN is relatively resilient to early malnutrition.
Abstract:
We investigated in young rats the effects of malnutrition on the main structures of the circadian timing system: retina, hypothalamic suprachiasmatic nuclei (SCN), thalamic intergeniculate leaflet, retinohypothalamic- and geniculohypothalamic tracts. Control rats were born from mothers fed a commercial diet since gestation, and malnourished rats from mothers fed a multideficient diet since gestation (GLA group) or lactation (LA group). After weaning, pups received the same diet as their mothers, and were analysed at postnatal days 27, 30-33 and 60-63. Brain sections were processed to visualise in the SCN neuropeptide Y immunoreactivity and terminal labeling after intraocular tracer injections. Nissl staining was used to assess cytoarchitectonic boundaries of the SCN and cell features in retinal whole mounts. Cell counts, morphometric and densitometric analysis were performed. Compared with controls, the total retinal surface was reduced and the topographical distribution of retinal ganglion cells was altered in malnourished rats, with changes in their density. Alterations were also detected in the SCN dimensions in the GLA and LA groups at one and two postnatal months, as well as in the SCN portion occupied by the retinal input in the GLA group at days 30-33, but not in the NPY-containing geniculohypothalamic tract. The present data point to subtle changes, with a low and differential vulnerability to early malnutrition, of structures involved in circadian timing regulation. Furthermore, the present findings suggest that the altered circadian rhythmicity previously documented in malnourished rats cannot be ascribed to impaired development of the retino- and geniculohypothalamic projections to the SCN.
