Increased apoptosis and decreased volume in the nucleus reuniens of the midline thalamus following alcohol exposure in a third trimester model of FASDs

Abstract

Fetal alcohol spectrum disorders (FASDs) is a term used to encompass an array of disorders that result from the consumption of alcohol during pregnancy. Approximately 2-5% of live births in the United States are diagnosed with FASDs, despite being entirely preventable. FASDs range in symptoms, which range from facial abnormalities to cognitive deficits. While facial abnormalities do not usually extend past early trimester exposure, cognitive deficits, such as deficits in executive functioning (EF), can still occur following a third trimester alcohol exposure. EF relies on the communication between the hippocampus (HPC) and medial prefrontal cortex (mPFC) through circuitry involving the midline thalamic nucleus reuniens (Re), suggesting that deficits seen in FASDs are due in part to damage of Re. ☐ The current study used a rodent model of third trimester FASDs to examine the damage to Re following a single day alcohol exposure on postnatal day (PD) 9. Re damage was characterized in this study by the estimation of apoptotic cell number 12 hours after alcohol exposure, estimation of total cell number in adulthood, estimation of neuron and astrocyte numbers in adulthood, and estimation of volume of the region. Long Evans rats were either administered a high dose of alcohol (5.25 g/kg/day; AEhigh), moderate dose of alcohol (3.0 g/kg/day; AEmod), or were sham intubated (SI) on PD9. Rats were sacrificed either 12 hours after exposure on PD9, or on PD65. Brain sections were stained with cresyl violet or fluorescent anti-NeuN (against neurons) and anti-GFAP (against astrocytes). Cresyl violet was used to visualize and estimate total cell number (PD65) and to visualize and estimate the number of apoptotic cells (PD9) in Re. Fluorescent anti-NeuN and anti-GFAP were used to visualize and quantify mature neurons and astrocytes, respectively, in Re on PD65. ☐ The number of apoptotic cells in Re on PD9 12 hours after alcohol exposure was significantly different across postnatal treatments, such that pups in the AEhigh treatment had significantly more apoptotic cells in Re when compared to SI pups and pups in the AEmod treatment. A main effect of sex was also seen, as females showed significantly greater levels of apoptosis in Re than males. Postnatal treatment also significantly affected the volume of Re on PD9 12 hours after exposure, such that pups in the AEmod treatment had a significantly lower volume of Re when compared to SI pups and pups in the AEhigh treatment. No significant effects of alcohol exposure were seen on total cell number, neuron number, astrocyte number, or volume on PD65. These results indicate that the Re is directly damaged following alcohol exposure exemplified by higher levels of cell death and decreased volume when compared to controls, but differences in cell number and volume between conditions were not observed in adulthood, suggesting that the damage to Re directly following AE is not sustained.