Leptin signaling in the hypothalamus is obligatory for normal food intake and body weight homeostasis. It is now well established that besides the signal transducer and activator of transcription-3 (STAT3) pathway, several non-STAT3 pathways mediate leptin signaling in the hypothalamus. We have previously demonstrated that leptin stimulates phosphodiesterase-3B (PDE3B) activity in the hypothalamus, and PDE3 inhibitor cilostamide reverses anorectic and bodyweight reducing effects of leptin. Recently, we have demonstrated that cilostamide reversed the leptin-induced increase in proopiomelanocortin (POMC) gene expression in the hypothalamus. Because POMC and neuropeptide Y (NPY) neurons are thought to be the major targets of leptin signaling in the hypothalamus, to establish the physiological role of the PDE3B pathway it is important to demonstrate if PDE3B is expressed in these neurons. To this end we examined co-localization of PDE3B with POMC and NPY neurons using immunocytochemistry in POMC-GFP and NPY-GFP mice, respectively. Results showed that PDE3B was highly localized throughout the various hypothalamic sites including the arcuate nucleus (ARC), ventromedial nucleus, dorsomedial nucleus, ventral premammillary nucleus, paraventricular nucleus, and lateral hypothalamus. Importantly, almost all NPY (91.7%) and POMC (97.7%) neurons co-expressed PDE3B. These results suggest a direct role of the PDE3B pathway in mediating leptin signaling in the POMC and NPY neurons –a potential mechanism of leptin signaling in the hypothalamus.

Key points Compared with sham rats, rats a week after acute lung injury (ALI) express more pro‐inflammatory cytokines in their brainstem respiratory control nuclei, exhibit a higher respiratory frequency (fR) and breathe with a more predictable pattern. These characteristics of the respiratory pattern persist in in situ preparations even after minimizing pulmonary and chemo‐afferent inputs. Interleukin (IL)‐1β microinjected in the nucleus tractus solitarii increases fR and the predictability of the ventilatory pattern similar to rats with ALI. Intracerebroventricular infusion of indomethacin, an anti‐inflammatory drug, mitigates the effect of ALI on fR and ventilatory pattern variability. We conclude that changes in the ventilatory pattern after ALI result not only from sensory input due to pulmonary damage and dysfunction but also from neuro‐inflammation. AbstractAcute lung injury (ALI) increases respiratory rate (fR) and ventilatory pattern variability (VPV), but also evokes peripheral and central inflammation. We hypothesized that central inflammation has a role in determining the ventilatory pattern after ALI. In rat pups, we intratracheally injected either bleomycin to induce ALI or saline as a sham control. One week later, we recorded the ventilatory pattern of the rat pups using flow‐through plethysmography, then formed in situ preparations from these pups and recorded their ‘fictive’ patterns from respiratory motor nerves. Compared with the ventilatory pattern of the sham rat pups, injured rat pups had increased fR and predictability. Surprisingly, the fictive patterns of the in situ preparations from ALI pups retained these characteristics despite removing their lungs to eliminate pulmonary sensory inputs and perfusing them with hyperoxic artificial cerebral spinal fluid to minimize peripheral chemoreceptor input. Histological processing revealed increased immunoreactivity of the pro‐inflammatory cytokine Interleukin‐1β (IL‐1β) in the nucleus tractus solitarii (nTS) from ALI but not sham rats. In subsequent experiments, we microinjected IL‐1β in the nTS bilaterally in anaesthetized naïve adult rats, which increased fR and predictability of ventilatory pattern variability (VPV) after 2 h. Finally, we infused indomethacin intracerebroventricularly during the week of survival after ALI. This did not affect sham rats, but mitigated changes in fR and VPV in ALI rats. We conclude that neuro‐inflammation has an essential role in determining the ventilatory pattern of ALI rats.

Background: Intermittent hypoxic episodes are common among preterm infants, although longer term consequences on growth pattern and cardiovascular regulation are unclear. Furthermore, the effects of intermittent hypoxia (IH) may depend on the pattern of hypoxia-reoxygenation. Objectives: We tested the hypothesis that a clustered versus dispersed pattern of repetitive IH during early postnatal life would induce differential long-term alteration in growth and cardiovascular regulation. Methods: Sprague-Dawley rat pups were exposed to room air or to one of two patterns of IH (clustered vs. dispersed) from 1 to 7 days of life. Body weight was measured daily for the first 8 days and weekly from weeks 2 to 8. Blood pressure (BP) and heart rate were measured weekly from weeks 4 to 8 using a noninvasive tail-cuff method for awake, nonanesthetized animals. Results: Exposure to both patterns of repetitive IH induced early growth restriction followed by later catch-up of growth to controls 3 weeks after completion of IH exposures. IH-exposed rats exhibited a sustained decrease in heart rate regardless of the hypoxic exposure paradigm employed. In contrast, a differential response was seen for arterial pressure; the clustered paradigm was associated with a significantly lower BP versus controls, while the pups exposed to the dispersed paradigm showed no effect on BP. Conclusion: We speculate that repetitive IH during a critical developmental window and regardless of IH exposure paradigm contributes to prolonged changes in sympathovagal balance of cardiovascular regulation.