Int'l Guest Spkr Professor Christian Broberger MD, Dept. of Neuroscience, Karolinska Institute - ‘Neurons and transmitter actions that underlie the switch between network states associated with sleep and wakefulness’

Tuberoinfundibular dopamine (TIDA) neurons in the hypothalamus control pituitary hormone release and play a central role in regulating fertility and parental behaviours. The recent demonstration that rat TIDA neurons in vitro exhibit a remarkably robust and regular membrane potential oscillation suggests that the system can also be used to study how neuronal ensembles organize into rhythmic output. We have recently made the unexpected discovery of a striking species difference in the TIDA system, where rat TIDA cells discharge in slow, stereotyped and synchronized oscillations, whereas the mouse displays a wide range of faster, asynchronous rhythms. Through electrophysiology, imaging and immunofluorescence, we could attribute this difference to the presence of powerful (coupling coefficient 0.18) gap junction connectivity in the rat, but a total absence of electrical coupling in the mouse. Resonance studies suggest that gap junctions mask a substantial heterogeneity within the rat network, and harmonizes the network according to the slowest cell in the population. Furthermore, the presence of dynamic coupling helps the network to maximize synchronization towards the spiking phase of the duty cycle. The TIDA species difference allows for new insight into the broader role of gap junction coupling in neuronal networks.