Characteristics of Rostral Solitary Tract Nucleus Neurons With Identified Afferent Connections That Project to the Parabrachial Nucleus in Rats

Abstract

Suwabe T, Bradley RM. Characteristics of rostral solitary tract nucleus neurons with identified afferent connections that project to the parabrachial nucleus in rats. J Neurophysiol 102: 546 -555, 2009. First published May 13, 2009 doi:10.1152/jn.91182.2008. Afferent information derived from oral chemoreceptors is transmitted to second-order neurons in the rostral solitary tract nucleus (rNST) and then relayed to other CNS locations responsible for complex sensory and motor behaviors. Here we investigate the characteristics of rNST neurons sending information rostrally to the parabrachial nucleus (PBN). Afferent connections to these rNST-PBN projection neurons were identified by anterograde labeling of the chorda tympani (CT), glossopharyngeal (IX), and lingual (LV) nerves. We used voltage-and current-clamp recordings in brain slices to characterize the expression of both the transient A-type potassium current, I KA and the hyperpolarization-activated inward current, I h , important determinants of neuronal repetitive discharge characteristics. The majority of rNST-PBN neurons express I KA , and these I KA -expressing neurons predominate in CT and IX terminal fields but were expressed in approximately half of the neurons in the LV field. rNST-PBN neurons expressing I h were evenly distributed among CT, IX and LV terminal fields. However, expression patterns of I KA and I h differed among CT, IX, and LV fields. I KA -expressing neurons frequently coexpress I h in CT and IX terminal fields, whereas neurons in LV terminal field often express only I h . After GABA A receptor block all rNST-PBN neurons responded to afferent stimulation with all-or-none excitatory synaptic responses. rNST-PBN neurons had either multipolar or elongate morphologies and were distributed throughout the rNST, but multipolar neurons were more often encountered in CT and IX terminal fields. No correlation was found between the biophysical and morphological characteristics of the rNST-PBN projection neurons in each terminal field. I N T R O D U C T I O NThe rostral nucleus of the solitary tract (rNST) is the first central relay in the taste pathway (reviewed in Bradley 2006). Sensory information originating from taste buds and other receptors in the oral cavity is relayed to the CNS via afferent nerve fibers of the facial and glossopharyngeal nerves. The central processes of these nerves form the solitary tract (ST), which travels caudally in the brain stem giving off branches that terminate within the rNST (Hamilton and Norgren 1984;May and Hill 2006). The chorda tympani (CT) and greater superficial petrosal branches of the facial nerve innervate the anterior tongue and palate, respectively, and project to the most rostral portions of the nucleus. The terminals of these branches of the facial nerve intermingle within a region of the dorsal rNST just medial to the ST; an area corresponding to rostralcentral and medial rostral-lateral subdivisions (Whitehead 1988). The lingual-tonsilar branch of the glossopharyngeal nerve (IX) transmits senso...

Pre- and postnatal differences in membrane, action potential, and ion channel properties of rostral nucleus of the solitary tract neurons

“…The I KA influences the repetitive firing pattern of adult rNST neurons (Suwabe and Bradley 2009;Tell and Bradley 1994;Uteshev and Smith 2006). We determined prenatal development of I KA in rNST neurons using voltage protocols and 4-AP blocking.…”

Gustatory System

“…Based on their membrane characteristics, anterior Sol cells come in two varieties also in a roughly 70/30 ratio (Bradley and Sweazey, 1990). Current injection studies reveal four different characteristic patterns in anterior Sol neurons, but apparently they do not correlate with cell morphology (Bradley and Sweazey, 1992;Suwabe and Bradley, 2009). Except for the fact that more of the larger cells are located ventrally, the differentiation based on nuclear characteristics does not obviously match the cytoarchitectonic subdivisions.…”

“…The rostrocentral subdivision and its caudal extension receive most of the primary afferent terminations from the chorda tympani and glossopharyngeal nerves, and provide most of the efferent projections to the parabrachial nuclei (Whitehead, 1990;Suwabe and Bradley, 2009). The rostrolateral subdivision receives sensory terminations primarily from the lingual nerve; the other three areas get little peripheral input at all.…”

Properties of GABAergic Neurons in the Rostral Solitary Tract Nucleus in Mice

“…It is perhaps significant that the M-current is augmented by somatostatin (Moore et al 1988), which we have shown to be present in fibers throughout the rNST. The initial burst neurons would initiate brief inhibitory activity and therefore potentially hyperpolarize the second-order rNST neurons activating the A-current that many of these neurons express (Suwabe and Bradley 2009;Tell and Bradley 1994;Uteshev and Smith 2006). Thus the burst neurons would play an important role in sensory processing by changing the afferent excitatory response in secondorder rNST neurons.…”