Heterogeneous receptor distribution in autonomic neurons

The central nervous system components for baroreflex regulation of sympathetic outflow include specific sets of neurons in the brain and spinal cord. Critical nuclei containing sympathetic baroreceptive neurons are the nuclei of the solitary tract, regions of the caudal and rostral ventrolateral medulla, and the intermediolateral cell column in the spinal cord. While many other brain regions project to these nuclei, cells in these areas appear to form the minimal required pathway for baroreflex control of sympathetic outflow. Synaptic connections have been identified between cells in these nuclei that are consistent with a serial relay from baroreceptor afferents through the brain stem and to sympathetic preganglionic neurons in the spinal cord. In recent years, we have examined the distribution of receptor proteins in these neurons, with a focus on receptors that are most likely to modulate the activity of these cells. In three studies examining the distribution of different receptors on distinct neurons, each study found some type of heterogeneity in the distribution of each receptor within a particular type of neuron. This heterogeneity was seen with regard to the distribution of receptor protein within the dendritic tree of individual neurons, as well as between pre- and postsynaptic sites on the same cell. This heterogeneous distribution of receptors suggests that receptors undergo dendritic targeting within autonomic neurons. This receptor trafficking may be regulated by heterogeneous afferent input to autonomic neurons and could be changed under conditions where afferent activity is significantly altered.