Responses of Neurons in the Medullary Lateral Tegmental Field and Nucleus Tractus Solitarius to Vestibular Stimuli in Conscious Felines

Abstract

Considerable evidence shows that the vestibular system contributes to adjusting sympathetic nervous system activity to maintain adequate blood pressure during movement and changes in posture. However, only a few prior experiments entailed recordings in conscious animals from brainstem neurons presumed to convey baroreceptor and vestibular inputs to neurons in the rostral ventrolateral medulla (RVLM) that provide inputs to sympathetic preganglionic neurons in the spinal cord. In this study, recordings were made in conscious felines from neurons in the medullary lateral tegmental field (LTF) and nucleus tractus solitarius (NTS) identified as regulating sympathetic nervous system activity by exhibiting changes in firing rate related to the cardiac cycle, or cardiac-related activity (CRA). Approximately 38% of LTF and NTS neurons responded to static 40° head up tilts with a change in firing rate (increase for 60% of the neurons, decrease for 40%) of ~50%. However, few of these neurons responded to 10° sinusoidal rotations in the pitch plane, in contrast to prior findings in decerebrate animals that the firing rates of both NTS and LTF neurons are modulated by small-amplitude body rotations. Thus, as previously demonstrated for RVLM neurons, in conscious animals NTS and LTF neurons only respond to large rotations that lead to changes in sympathetic nervous system activity. The similar responses to head-up rotations of LTF and NTS neurons with those documented for RVLM neurons suggest that LTF and NTS neurons are components of the vestibulo-sympathetic reflex pathway. However, a difference between NTS/LTF and RVLM neurons was variability in CRA over time. This variability was significantly greater for RVLM neurons, raising the hypothesis that the responsiveness of these neurons to baroreceptor input is adjusted based on the animal's vigilance and alertness.

Physiological changes associated with copper sulfate-induced nausea and retching in felines

“…As in our prior experiments ( Patel et al, 2018 ; Bielanin et al, 2020 ; Miller et al, 2020 ), animals were gradually acclimated over at least 5 weeks for 1-h of confinement in a nylon restraint bag attached to a recording platform using Velcro straps. Subsequently, an aseptic recovery surgery was performed in a dedicated operating suite as described below to attach two-contact platinum-iridium 90/10 electrodes in a silicone patch (Micro-leads Inc, Somerville, MA, United States), similar to those used in prior studies ( Nanivadekar et al, 2019 ; Shulgach et al, 2021 ), to the proximal duodenum and gastric antrum, on the ventral surface ( Figure 1 ).…”

Physiological Changes Associated with Copper Sulfate-Induced Emesis in Felines

“…As in our prior experiments (Patel et al, 2018; Bielanin et al, 2020; Miller et al, 2020), animals were gradually acclimated over at least 5 weeks for 1-hour of confinement in a nylon restraint bag attached to a recording platform using Velcro straps. Subsequently, an aseptic recovery surgery was performed in a dedicated operating suite as described below to attach two-contact platinum-iridium 90/10 electrodes in a silicone patch (Micro-leads Inc., Somerville, MA, USA), similar to those used in prior studies (Nanivadekar et al, 2019; Shulgach et al, 2021), to the proximal duodenum and gastric antrum, on the ventral surface ( Figure 1 ).…”

Vestibular-autonomic interactions: beyond orthostatic dizziness

“…The vestibular-autonomic reflexes encompass numerous pathways triggered by vestibular activation, resulting in changes in sympathetic or parasympathetic outflows [4,5 vestibular nucleus to the parabrachial complex [6], which sends projections to brainstem and forebrain areas integrating vestibular sensation and autonomic control, and cerebellar modulation of brainstem areas mediating autonomic output [1,[7][8][9][10][11][12][13]. Various sites within the cerebellum (anterior lobe, rostral posterior lobe, caudal posterior lobe-nodulus) demonstrate the ability to influence sympathetic and parasympathetic reflexes [14][15][16]17 && ]. The central vestibular sensation and autonomic control systems are highly interconnected and converge within the insular cortex.…”

“…Primary pathways include a descending tract from the inferior vestibular nucleus to the dorsal motor nucleus of the vagus and the ventrolateral medulla, an ascending pathway from the rostral vestibular nucleus to the parabrachial complex [6], which sends projections to brainstem and forebrain areas integrating vestibular sensation and autonomic control, and cerebellar modulation of brainstem areas mediating autonomic output [1,7–13]. Various sites within the cerebellum (anterior lobe, rostral posterior lobe, caudal posterior lobe-nodulus) demonstrate the ability to influence sympathetic and parasympathetic reflexes [14–16,17 ▪▪ ].…”