Relationship between structure and function of neurons in the rat rostral nucleus tractus solitarii

Abstract

To investigate the relationship between the structure and function of neurons in the rostral (gustatory) nucleus tractus solitarii (rNTS), we analyzed the morphological and biophysical properties of rNTS neurons by performing whole-cell recordings in a brain slice preparation. Overall, neurons (n = 58) had a mean somal diameter of 16 microns, an average dendritic length of 598 microns, an average dendritic thickness of 0.91 microns, and a spine density of 0.037 spines/microns. Neurons were separated into three groups (elongate, multipolar, and ovoid) on the basis of previously established morphological criteria. The highest percentage (49%) of neurons were classified as ovoid, while 35% were multipolar and only 16% were elongate. The most frequently observed firing pattern, in all three cell types, elicited by a 1,200 ms, 100 pA depolarizing current pulse was a regularly firing spike train. However, the intrinsic firing properties of the remaining neurons were different. Thirty-one percent of the ovoid neurons responded with a short burst of action potentials and 44% of the elongate neurons showed a delay in the onset of the spike train following a hyperpolarizing prepulse. Less than 16% of the multipolar neurons demonstrated either of these firing characteristics. Therefore, rNTS neurons with similar morphology do not have unique biophysical properties. However, the data suggest that there may be subpopulations of the three morphological types, each of which displays a different firing pattern. Since the structure and function of the three morphological groups were not strictly correlated, these subpopulations may represent functional groups.

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

“…Our data also confirm that rNST projection neurons fall into these same two morphological groups. No correlation was found between neuron morphology, intrinsic membrane properties and voltage-gated conductances when attempts were made to group rNST neurons in "blind" patchclamp recordings (King and Bradley 1994;Uteshev and Smith 2006). Thus rNST neurons with different morphologies can not be separated into groups based on biophysical properties yet can be separated based on responses to chemical, mechanical, and thermal stimulation of the oral cavity.…”

“…7) or multipolar ("M" in Fig. 7) based on soma shape, number of primary dendrites and the sites where dendrites originated on the soma (King and Bradley 1994;King and Hill 1993;Lasiter et al 1989;Mistretta and Labyak 1994;Whitehead 1990). Elongate neurons had fusiform to ovoid cell bodies with two primary dendrites exiting the cell body from opposite poles.…”

Organization of excitatory and inhibitory local networks in the caudal nucleus of tractus solitarius of rats revealed in in vitro slice preparation

“…Medium to large NTS neurons constitute heterogeneous populations in terms of their passive membrane properties and somato-dendritic morphology (Paton et al, 1993;King excitatory network, and their main axons probably project to the parabrachial nucleus. The inhibitory cells are presumably interneurons that connect the excitatory network with medium to large projection neurons.…”

Synaptic and morphologic properties in vitro of premotor rat nucleus tractus solitarius neurons labeled transneuronally from the stomach

“…Neurons in the NTS interact with each other and with neurons in several other central autonomic areas (Sawchenko and Swanson, 1982;Spyer et al, 1984;Agarwal and Calaresu, 1990;Rogers and McCann, 1993). Perhaps related to the diverse nature of synaptic connectivity in the region, caudal NTS neurons display a variety of phenotypic and morphologic characteristics, which may be correlated with the type of local and visceral synaptic inputs regulating their activity Champagnat et al, 1986;King and Bradley, 1994; Senba, 1996, 2000).In addition to integrating synaptic input, NTS neurons participate in vagal reflexes by means of synaptic connections with neurons in the dorsal motor nucleus of the vagus nerve (DMV), which provide the primary source of preganglionic motor output to the stomach and other subdiaphragmatic viscera. Electrical stimulation of the NTS results in excitatory or inhibitory synaptic currents in the DMV, consistent with the hypothesis that both ␥-aminobutyric acid (GABA) -ergic and glutamatergic connections exist between the NTS to the DMV (Travagli et al, 1991).…”