Diet-Induced Modulation of Brainstem Perineuronal Net Development
Open Access
- Author:
- Morehouse, Jessica
- Graduate Program:
- Anatomy
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- March 02, 2022
- Committee Members:
- Patricia Mclaughlin, Program Head/Chair
Kirsteen Browning, Thesis Advisor/Co-Advisor
Anirban Paul, Committee Member - Keywords:
- Perinatal high fat diet (PNHFD)
Dorsal motor nucleus of the vagus (DMV)
Obesity
Brainstem
Neuroplasticity - Abstract:
- The prevalence of obesity has increased dramatically worldwide, accompanied by an increase in comorbid conditions such as heart disease and type II diabetes. While obesity is associated with a combination of genetic and environmental causes, the perinatal period is known to be critical for the development of autonomic neurocircuits, including vagal reflexes involved in the regulation of energy expenditure and food intake, including gastric motility, tone, and emptying. Previous work from this lab has demonstrated that, in rats, exposure to a perinatal high fat diet (PNHFD) results in a decrease in the excitability of neurons within the dorsal motor nucleus of the vagus (DMV), due to a disruption in the developmental expression of synaptic GABAA receptors. The development of perineuronal nets (PNNs), extracellular matrix structures that are known to limit neuroplasticity, coincides with critical periods of development in regions such as the hypothalamic arcuate nucleus, which is also involved in autonomic regulation of energy balance and is disrupted when exposed to a PNHFD. It is unclear, however, what the developmental time course of PNN maturation in the brainstem is and whether it is similarly disrupted by PNHFD exposure. The aims of this study were to determine the time course of development of PNNs within the DMV and examine whether PNHFD exposure is impacted by PNHFD exposure. To investigate this, Sprague Dawley rats were exposed to either a control diet (14% kcal from fat) or PNHFD (60% kcal from fat) from embryonic day 13 (when vagal neurocircuits first start developing) until the point of sacrifice (various time points from postnatal day 7 (P7) until postnatal day 56 (P56)). Immunohistochemistry was used to identify PNN components (chondroitin sulphate proteoglycans (CSPGs), hyaluronan (HA), and semaphorin-3A (Sema3A)), as well as cholinergic neurons within the DMV. The average fluorescent density for each antigen was determined using Image J analysis of confocal microscopic images of caudal, intermediate, and rostral brainstem slices. Rats exposed to a PNHFD demonstrated a delayed development of HA within the DMV, with levels significantly lower than control pups at P7 (P < 0.0001) and P14 (P = 0.0418) although differences were no longer apparent by P21 and timepoints thereafter. Sema3A staining was significantly decreased in PNHFD compared to control pups between P14 (P = 0.0036) and P21 (P = 0.0078), with no significance at P28. Unlike HA, by P56, PNHFD rats displayed a significantly increased level of Sema3A staining (P = 0.0001) compared to control rats, thus indicating a time in which rats exposed to a PNHFD may exhibit less plasticity than rats exposed to a control diet. Wisteria floribunda lectin (WFA; used to stain CSPG and acts as an indirect measure of PNN maturation, with greater staining intensity corresponding to a more mature PNN) staining was significantly less intense in PNHFD rats compared to control rats at all time points, although the pattern of development was similar between both diet groups. The results of the present study demonstrate that exposure to a PNHFD causes a delay in PNN development within the brainstem and suggests a mechanism by which neuroplasticity within the DMV is altered. Specifically, a delayed development of PNNs caused by exposure to a PNHFD may extend the critical period of development where neuroplasticity and the maturation of vagal neurocircuits occurs. This delay could potentially explain the increased inhibitory GABAergic drive to DMV neurons that is seen following PNHFD, which leads to decreases in gastric motility and tone, thus altering the ability of vagal neurocircuits to regulate feeding behavior.