Modulatory actions of serotonin, noradrenaline and dopamine

These neuromodulatory transmitters arise from descending systems to control spinal sensory integration. We provided the first comparative analysis of their actions on synaptic and cellular properties of spinal sensory encoding neurons. These modulators acted in a comparable and predictable manner; to profoundly depress sensory input yet increase cell excitability. With Jorge Quevedo, we looked more specifically at modulation of afferents arising from muscle and cutaneous nerves, and again found broadly uniform actions – depression of afferent input. My lab then looked at actions arising from visceral afferents, again observing broad depression. Yet, in all above studies, subtly different responses for each monoamine were seen. Thus, the different monoamines, recruited by different brain systems during different behavioral drives, all include the general feature of reducing body sensations, particularly pain. In contrast, the actions of the monoamines on motor systems are generally facilitatory, but also differentiable. For example, noradrenaline promotes self-reinforcing positive feedback in spinal motor circuits while serotonin promoted negative feedback.

MACHACEK, D.W. & HOCHMAN, S. Noradrenaline unmasks novel self-reinforcing motor circuits within the mammalian spinal cord. J. Neurosci. 26:5920-8 (2006).

ZIMMERMAN, A., SAWCHUK,M., & HOCHMAN, S. Monoaminergic modulation of spinal viscero-sympathetic function in the neonatal mouse thoracic spinal cord. PLoS One. 7(11):e47213. doi: 10.1371/journal.pone.0047213. (2012) PMID: 23144807