Somatostatin triggers rhythmic electrical firing in hypothalamic GHRH neurons.

Hypothalamic growth hormone-releasing hormone (GHRH) neurons orchestrate body growth/maturation and have been implicated in feeding responses and ageing. However, the electrical patterns that dictate GHRH neuron functions have remained elusive. Since the inhibitory neuropeptide somatostatin (SST) is considered to be a primary oscillator of the GH axis, we examined its acute effects on GHRH neurons in brain slices from male and female GHRH-GFP mice. At the cellular level, SST irregularly suppressed GHRH neuron electrical activity, leading to slow oscillations at the population level. This resulted from an initial inhibitory action at the GHRH neuron level via K(+) channel activation, followed by a delayed, sst1/sst2 receptor-dependent unbalancing of glutamatergic and GABAergic synaptic inputs. The oscillation patterns induced by SST were sexually dimorphic, and could be explained by differential actions of SST on both GABAergic and glutamatergic currents. Thus, a tripartite neuronal circuit involving a fast hyperpolarization and a dual regulation of synaptic inputs appeared sufficient in pacing the activity of the GHRH neuronal population. These "feed-forward loops" may represent basic building blocks involved in the regulation of GHRH release and its downstream sexual specific functions.

Supine sleep and obstructive sleep apnea syndrome in Parkinson's disease.

OBJECTIVE: Supine sleep is associated with increased obstructive sleep apnea. People with Parkinson's disease (PD) complain about difficulties turning around in bed. The relationship between supine sleep and sleep-disordered breathing has never been explored in people with Parkinson's disease. METHODS: Fifteen consecutive people with PD with severe Obstructive Sleep Apnea Syndrome (OSAS) were compared to: (1) 15 age-matched, gender-matched, body mass index-matched and Unified Parkinson's Disease Rating Scale-III score-matched people with PD without sleep-disordered breathing; (2) 11 age-matched and gender-matched people with severe obstructive sleep apnea syndrome (OSAS) alone; and (3) 11 age-matched and gender-matched healthy controls. Outcomes were: number of position changes during the night and per hour of sleep, and the percentage of sleep time spent in supine. RESULTS: People with PD and severe OSAS spent most of their sleep time in the supine position (93 ± 11%); while people with PD without OSAS (61 ± 24%, p <0.001), people with isolated, severe OSAS (50 ± 28%, p <0.001), and the controls (40 ± 21, p <0.001) spent significantly less time on their back. People with PD and severe OSAS changed their position in bed per hour of sleep (0.4 ± 0.5) less frequently than those with PD without OSAS (1.1 ± 0.8, p = 0.002), those with isolated OSAS (1.2 ± 1.0, p = 0.006) and the controls (1.5 ± 0.5, p <0.001). CONCLUSION: PD and severe OSAS are associated with a major reduction in the number of position changes and an increased supine sleep position during the night. For people with PD, alleviating the difficulties of turning around in bed might reduce the supine sleep position and improve sleep-disordered breathing.