Orexin A enhances neuronal synchronization in adult rat hypothalamic culture: A model to study hypothalamic function.

BACKGROUND: The regulation of sleep/wake behavior and energy homeostasis is maintained in part by the lateral hypothalamic (LH) neuropeptide orexin A (OXA, hypocretin). A reduction in orexin signaling is associated with sleep disorders and obesity, whereas higher LH orexin signaling and sensitivity promotes obesity resistance. Similarly, dysregulation of hypothalamic neural networks is associated with onset of age-related diseases, including obesity and several neurological diseases. Despite the increase in obesity with aging, and that adult populations are the subjects in the majority of pharmaceutical and obesity studies, conventional models for neuronal networks utilize embryonic neural cultures rather than adult neurons. Synchronous activity, a feature of normal brain function, and a measure of functional connectivity, describes correlated changes in neuronal activity between neurons, Synchronization determines the nature of the final output from a given neural structure. Neural synchrony is altered by behavioral perturbations, in embryonic neurons obtained from obesity-resistant rats, and following application of OXA onto embryonic hypothalamic cultures. Synchronous network dynamics in adult hypothalamic neurons remain largely undescribed.

METHODS: We established an adult rat hypothalamic culture in multi-electrode-array (MEA) dishes and recorded the field potentials. Then we studied the effect of exogenous OXA on network synchronization of these adult hypothalamic cultures. In addition, we studied the wake promoting effects of OXA in vivo when directly injected into the rostral lateral hypothalamus (rLH). To study the wake promoting effects of LH OXA, rats were implanted with a radiotelemetric transmitter and EEG/EMG electrodes to record vigilance states (F40-EET, Data Sciences International [DSI], St. Paul, MN), and a cannula targeting the rLH. Following surgical recovery, either OXA (250 pmol/0.5 μl) or saline was infused into the rLH (single injection) and sleep/wake states were measured for 2h post-injection.

RESULTS: The results show that adult hypothalamic cultures are viable for nearly 3 months in vitro, good quality MEA recordings can be obtained from these cultures in vitro, and finally, that cultured adult hypothalamus is responsive to OXA. In addition, LH administration of OXA enhanced wakefulness in rats, indicating that OXA enhances wakefulness for up to 2h post-injection.

CONCLUSIONS: These results support that adult rat hypothalamic cultures could be used as a model to study the neural mechanisms underlying obesity, and that obesity resistance is associated with increased hypothalamus synchronization. Increased wake following rLH OXA suggest the possibility that OXA promotes wake partly by promoting neural synchrony in the hypothalamus.