Extreme Dehydration in Desert Gerbils Induces SFO Astrocyte Plasticity and Increases SON Vasopressin/Oxytocin Expression

The central nervous system critically regulates water and electrolyte balance, primarily through circumventricular organs (CVOs) like the subfornical organ (SFO) and the hypothalamo-neurohypophysial system. Despite the remarkable ability of desert rodents, such as Gerbillus tarabuli, to thrive in arid conditions, the specific neuroendocrine mechanisms underpinning their hydromineral adaptation remain largely uncharacterized. Understanding these unique physiological responses can shed light on fundamental principles of homeostasis and survival under extreme environmental stress, addressing a significant gap in comparative neuroendocrinology.

Researchers investigated the effects of long-term dehydration (4 weeks) in Gerbillus tarabuli desert rodents. They assessed physiological parameters including body mass, plasma osmolality, sodium concentration, hematocrit, and glycemia. The study focused on glial fibrillary acidic protein (GFAP) expression in the SFO, and vasopressin (VP) and oxytocin (OT) expression in magnocellular neurons (MCNs) of the supraoptic nucleus (SON) using immunohistochemistry. Euhydrated gerbils served as the control group for all comparisons, allowing for direct evaluation of dehydration-induced changes.

Dehydrated gerbils showed no significant differences in body mass, plasma osmolality, natremia, or glycemia compared to euhydrated controls. However, hematocrit was significantly increased by 5.53%, indicating a 15.97% reduction in plasma volume. Long-term dehydration profoundly impacted brain structures involved in fluid balance. Specifically, the SFO exhibited a marked increase in GFAP immunoreactivity, suggesting significant astrocyte plasticity. Concurrently, the SON displayed a significant increase in both VP and OT immunoreactivity, coupled with an enlargement of MCN soma size. This indicates heightened neurosecretory activity. Additionally, the SON of G. tarabuli demonstrated a unique mediolateral extension in the dorsolateral region of the optic chiasm (OC).