An old colleague of mine used to liken the autonomic nervous system to the suburbs of a city in a condescending way: “why bother going there if there's never anything going on?”. Of course, this patronizing view is quite inaccurate; we may not know a lot about what happens in the periphery, but this should actually encourage us to find out more about it. Take, for example, the physiology of the sympathetic neurons that control vasomotor tone. These postganglionic cells show bursts of activity with a periodicity that is related to the cardiac and respiratory cycles, a coordination that might help to optimize blood supply to every organ. How is this bursting activity controlled? One leading idea is that an oscillatory network in the brainstem entrains the sympathetic neurons, causing them to fire synchronously. In fact, there seem to be not one, but several oscillatory networks, as there is variability in the rhythmic patterns of activity measured in the vascular systems of different organs. And now, a recent paper in The Journal of Physiology reports that afferent somatic activity can reset the oscillatory networks and transiently synchronize sympathetic neuron firing, adding an additional complication to this system.

Staras and his colleagues investigated the effect of radial nerve stimulation on the bursting firing of the postganglionic neurons that innervate the caudal ventral artery of the rat tail. They found that, following the stimulus, the activity of sympathetic neurons was first reduced and subsequently synchronized in a transient manner. The authors interpreted these findings as evidence that stimulation of the somatic nerve had reset the oscillatory networks, and proposed that this resetting could act to coordinate sympathetic function in response to somatic input. Indeed, this mechanism might have physiological relevance, as Staras et al. found that a similar transient synchronization also occurred when they applied a pinch to the rat paw. To discover whether a similar phenomenon is related to the enhanced bursts of sympathetic activity that are associated with stress in humans, we will have to take another trip to suburbia.