Coexistence of immune-neuro-endocrine substances in the rat central neurons

Neonatal lipopolysaccharide exposure alters central cytokine responses to stress in adulthood in Wistar rats

"Perinatal programming" is a phenomenon describing how early life environmental conditions can produce long-term physiological alterations that either enhance or inhibit adaptive functioning. Previously, we have demonstrated that neonatal exposure to lipopolysaccharide (LPS) predisposes to anxiety-like behaviour in later life, which was associated with changes to the neuroendocrine response to stress. Given the known interactions between the neuroendocrine and neuroimmune systems, here we investigated whether neonatal exposure to a bacterial mimetic alters neuroimmune responses to acute stress in adulthood. Male and female Wistar rats were administered LPS (0.05 mg/kg, i.p.), or saline vehicle (equivolume) on days 3 and 5 post-partum. One group of rats was euthanised following early life treatment to assess immediate hypothalamic-pituitary-adrenal axis and central cytokine responses to treatment. A second group was assessed in adulthood (85 days) following exposure to either a "stress" (30-min restraint) or "no stress" condition. Blood was collected from all rats at baseline, 30, 60 and 90 min after "stress", "no stress" treatment to assess peripheral corticosterone responses, and brains were collected 180 min following baseline to assess hippocampal content of interleukin-1β (IL-1β), tumour necrosis factor-α (TNFα) and IL-6 protein. Radioimmunoassay revealed that neonatal LPS treatment resulted in a prolonged corticosterone response to stress in adulthood compared to controls (p < 0.05). Enzyme-linked-immunosorbent assays revealed no group differences in hippocampal IL-6 content. However, brain IL-1β and TNFα protein concentrations were significantly greater in rats neonatally exposed to LPS and then exposed to stress in adulthood when compared to all other groups (p < 0.05). These findings suggest that early life bacterial toxin exposure results in a prolonged neuroendocrine response to acute stress in adulthood, which may be a consequence of increased release of IL-1β and TNFα in the brain.

The progesterone derivative dydrogesterone down-regulates neurokinin 1 receptor expression on lymphocytes, induces a Th2 skew and exerts hypoalgesic effects in mice

Accumulating evidence indicates that the neuropeptide substance P (SP) is predominantly involved in neurogenic inflammation and pain perception via its high-affinity neurokinin 1 receptor (NK-1R). Intriguingly, decreased pain sensitivity is found to be associated with high plasma progesterone levels. We hypothesize that progesterone may attenuate nociception and associated inflammatory response via NK-1R-dependent pathways. To address our hypothesis, we incubated splenic lymphocytes from CBA/J female mice with different concentrations of the progesterone derivative dydrogesterone. Subsequently, the expressions of NK-1R and T helper (Th1)-type cytokines were analyzed by flow cytometry. Next, we subcutaneously injected CBA/J mice with 1.25 mg of dydrogesterone in 200-microl sesame oil; control mice were sham-injected. Tail flick test to detect the nociceptive threshold was performed in 30-min intervals upon injection. Lymphocytes were isolated from blood and uterus and analyzed for NK-1R surface expression. Immunohistochemical analyses were performed to investigate the uterine tissue distribution of NK-1R. Dydrogesterone induced a decrease in the percentage of NK-1R+ lymphocytes in vitro and in vivo. Additionally, an increase in Th2-type and a decrease in Th1-type cytokines could be detected in vitro after incubation with dydrogesterone. An increased tail flick latency following dydrogesterone injection supported the concept that decreased expression of the NK-1R on lymphocytes is associated with an increased pain threshold. Taken together, these results clearly reveal a pathway by which dydrogesterone or progesterone respectively modulates the cross talk of the nervous, endocrine and immune systems in inflammation and pain.