Short-term but not long-term adrenalectomy modulates amplitude and frequency of the CRH41 episodic release in push-pull cannulated median eminence of free-moving rats.

International audienceCRH 41 release in push-pull cannulated median eminence (ME) was measured in unanesthetized male rats, 3 and 7 days after adrenalectomy (ADX) and in sham-lesioned controls. Perfusion started at 13.30 h and perfusate samples were collected at 5 min intervals for 3 h to estimate the mean release rate of CRH41. The major parameters of the neurohormone's episodic release pattern were analyzed using the Ultra algorithm. In a parallel study, 3 groups of similarly treated rats were used to measure plasma ACTH and hypothalamic CRH41. Three days after ADX, the plasma ACTH titers had risen 14-fold, the hypothalamic CRH41 content had decreased by 40%, while the CRH41 release in the ME had doubled as a result of a significant increase in most variables of the pulsatile release pattern: pulse frequency (+34%; P < 0.01), mean amplitude (+36%; P < 0.05), mean peak levels (+67%; P < 0.01) and mean pulse nadirs (x2.5; P < 0.01). Seven days after ADX, even though plasma ACTH had further increased to 30-times control levels, hypothalamic CRH41 content and CRH41 release in the ME had returned to almost control levels. The possible mechanisms of the discrepancy between the CRH and ACTH response time-courses following ADX are discussed

A subpopulation of corticotropin-releasing hormone neurosecretory cells in the paraventricular nucleus of the hypothalamus also contain NADPH-diaphorase.

International audienceThe coexistence of ND with CRH 41 was explored in the parvicellular neurons of the PVN, using dual histochemical and radioimmunocytochemical labelling with the light microscope, in rats treated with colchicine. Even though the ND staining was scarce, a clear colocalization was evidenced in the parvicellular part of the PVN. Under these conditions, the ratio of neurons expressing both markers, ND and CRH, amounted about 15% of the CRH-containing neuron population. This result provides a useful tool to study morphological plastic changes in the PVN in response to environmental variations

Early hypothalamic activation of combined fos and CRH41 immunoreactivity and of CRH41 release in push-pull cannulated rats after systemic endotoxin challenge

International audienceWe previously showed that intra-arterial endotoxin infusion (lipopolysaccharide [LPS]: 25 micrograms.kg-1) induced an early (15 min) and sustained (480 min) rise in plasma ACTH associated with delayed (60-120 min) increases in plasma concentrations of TNF alpha, IL-6, and IL-1 beta. In the present study, we followed the post-LPS time-course of immunocytochemical expression of Fos-like activity in CRH41 neurons whose immunolabeling was enhanced by icv colchicine pretreatment 48 h before the LPS, and CRH41 release in the push-pull cannulated median eminence of free-moving rats, in parallel with the ACTH response. The earliest Fos-like activity in IR-CHR41 neurons was detected 30 min post-LPS. Colchicine strongly inhibited the LPS-induced activation of Fos expression in single-labeled paraventricular neurons. CRH41 release in the median eminence displayed a biphasic stimulation pattern, with a first peak (+60%) at 15 min together with the ACTH surge, followed by a second rise beginning at 45 min and lasting more than 2 h. Thus, the early stage of the ACTH surge following a nonlethal endotoxin challenge (< 60 min) already involves the activation of CRH41-producing neurons

[The corticotropic axis response after subcutaneous endotoxin injection is not associated with the increase of plasma interleukin-1 beta].

International audienceWhen injected through an intra-arterial (i. a.) cannula, LPS induced a rapid (15-30 min) and long-lasting (> 300 min) increase in plasma ACTH and corticosterone (CORT) levels. The duration of these responses depended on the LPS dose, and except for very small LPS doses, their amplitudes appeared independent of the dose of endotoxin. ACTH peaks (2,200 pg.ml-1) occurred between 30 and 120 min, whereas CORT always reached maximal levels at 120 min. Plasma Interleukin-1 beta (IL-1 beta) levels were always undetectable during the early phase of corticotropic stimulation, but increased strikingly 120 min after LPS injection. Increasing LPS doses, resulted in enhanced and prolonged IL-1 beta plasma circulating levels (up to 3.0 +/- 0.2 ng.ml-1). By contrast, no sub-cutaneous LPS dose used induced early increases in ACTH and CORT levels, whereas time-course of the hormonal response was evocative of the sustained phase of the corticotropic response to i. a. LPS, with both peaks occurring 120 min post-LPS. Increasing the s. c. LPS bolus 50-fold vs the i. a. dose did not affect the maximal amplitude of the ACTH response, whereas the amplitude of the CORT response, instead, appeared dependent on the LPS dose. On the other hand, even for the largest LPS doses, plasma IL-1 beta levels remained undetectable. Sub-cutaneous injection of LPS therefore appears as a new model for the study of the mechanisms of corticotropic responses to endotoxin without a direct involvement of bloodborne IL-1 beta