High-dose glucocorticoid aggravates TBI-associated corticosteroid insufficiency by inducing hypothalamic neuronal apoptosis

• It is the first time to observe the effects of GCs on hypothalamic neurons in vitro.
• We use the HPICM to observe neurons without mechanical contact and with nanoscaled resolution.
• We established the links between apoptosis of hypothalamic neurons and CIRCI after TBI.

Emerging experimental and clinical data suggest that severe illness, such as traumatic brain injury (TBI), can induce critical illness-related corticosteroid insufficiency (CIRCI). However, underlying mechanisms of this TBI-associated CIRCI remain poorly understood. We hypothesized that dexamethasone (DXM), a synthetic glucocorticoid, which was widely used to treat TBI, induces hypothalamic neuronal apoptosis to aggravate CIRCI. To test this hypothesis, we have evaluated the dose effect of DXM (1 or 10 mg/kg) on the development of acute CIRCI in rats with fluid percussion injury-induced TBI and on cultured rat hypothalamic neurons in vitro (DXM, 10−5–10−8 mol/L). Corticosterone Increase Index was recorded as the marker for CIRCI. In addition, MTT and TUNEL assays were used to measure the viability and apoptosis of hypothalamic neurons in primary culture. Moreover, high-resolution hopping probe ion conductance microscopy (HPICM) was used to monitor the DXM-induced morphological changes in neurons. The incidence of acute CIRCI was significantly higher in the high-dose DXM group on post-injury day 7. Cellular viability was significantly decreased from 12 h to 24 h after the treatment with a high-dose of DXM. A significantly increase in TUNEL positive cells were detected in cultured cells treated with a high-dose of DXM after 18 h. Neurites of hypothalamic neuron were dramatically thinner and the numbers of dendritic beadings increased in neurons treated with the high dose of DXM for 12 h. In conclusion, high-dose DXM induced hypothalamic neurons to undergo apoptosis in vivo and in vitro, which may aggravate TBI-associated CIRCI.