Effects of Feeding-Related Peptides on Neuronal Oscillation in the Ventromedial Hypothalamus

The ventromedial hypothalamus (VMH) plays an important role in feeding behavior, obesity, and thermoregulation. The VMH contains glucose-sensing neurons, the firing of which depends on the level of extracellular glucose and which are involved in maintaining the blood glucose level via the sympathetic nervous system. The VMH also expresses various receptors of the peptides related to feeding. However, it is not well-understood whether the action of feeding-related peptides mediates the activity of glucose-sensing neurons in the VMH. In the present study, we examined the effects of feeding-related peptides on the burst-generating property of the VMH. Superfusion with insulin, pituitary adenylate cyclase-activating polypeptide, corticotropin-releasing factor, and orexin increased the frequency of the VMH oscillation. In contrast, superfusion with leptin, cholecystokinin, cocaine- and amphetamine-regulated transcript, galanin, ghrelin, and neuropeptide Y decreased the frequency of the oscillation. Our findings indicated that the frequency changes of VMH oscillation in response to the application of feeding-related peptides showed a tendency similar to changes of sympathetic nerve activity in response to the application of these substances to the brain.

Beta oscillations and their functional role in movement perception

Neuronal oscillations refer to periodic changes of neuronal activity. A prominent neuronal oscillation, especially in sensorimotor areas, is the beta-frequency-band (∼ 13–29 Hz). Sensorimotor beta oscillations are predominantly linked to motor-related functions such as preparation and/or execution of movements. In addition, beta oscillations have been suggested to play a role in long-range communication between multiple brain areas. In this review, we assess different studies that show that sensorimotor beta oscillations are additionally involved in the visual perception and imagery of biological movements. We propose that sensorimotor beta oscillations reflect a mechanism of attempted matching to internally stored representations of movements. We additionally, provide evidence that beta oscillations play a role for the integration of visual and sensorimotor areas to a functional network that incorporates perceptual components at specific spatial-temporal profiles and transmits information across different areas.

Fast network oscillations in the hippocampus

Neuronal networks often express coherent oscillatory activity. These rhythms can pro­vide a temporal reference for the activity of single neurons and allow the formation of spatiotemporal activity patterns with a de­fined phase relationship of action potentials. In a single brain nucleus, oscillations at dif­ferent frequencies might be simultaneous­ly generated, but isolated rhythms might also be characteristic for specific functional brain states. During the last two decades the mam­malian hippocampus has become an impor­tant model system for the study of neuronal network oscillations. In this brain area, cel­lular mechanisms underlying neuronal syn­chronization have been described, but also models were developed to explain the con­tribution of oscillations in encoding, con­solidation, and recall of memories. Neuro­nal rhythmic activities provide an impor­tant field of analysis bringing together cel­lular mechanisms and systemic functions of the brain. Here, we use a particularly fast type of neuronal oscillation, hippocampal “rip­ples”, as an example to outline current knowl­edge and open questions related with this re­search field.