Identification of neural networks that contribute to motion sickness through principal components analysis of fos labeling induced by galvanic vestibular stimulation

Abstract

Motion sickness is a complex condition that includes both overt signs (e.g., vomiting) and more covert symptoms (e.g., anxiety and foreboding). The neural pathways that mediate these signs and symptoms are yet to identified. This study mapped the distribution of c-fos protein (Fos)-like immunoreactivity elicited during a galvanic vestibular stimulation paradigm that is known to induce motion sickness in felines. A principal components analysis was used to identify networks of neurons activated during this stimulus paradigm from functional correlations between Fos labeling in different nuclei. This analysis identified five principal components (neural networks) that accounted for greater than 95% of the variance in Fos labeling. Two of the components were correlated with the severity of motion sickness symptoms, and likely participated in generating the overt signs of the condition. One of these networks included neurons in locus coeruleus, medial, inferior and lateral vestibular nuclei, lateral nucleus tractus solitarius, medial parabrachial nucleus and periaqueductal gray. The second included neurons in the superior vestibular nucleus, precerebellar nuclei, periaqueductal gray, and parabrachial nuclei, with weaker associations of raphe nuclei. Three additional components (networks) were also identified that were not correlated with the severity of motion sickness symptoms. These networks likely mediated the covert aspects of motion sickness, such as affective components. The identification of five statistically independent component networks associated with the development of motion sickness provides an opportunity to consider, in network activation dimensions, the complex progression of signs and symptoms that are precipitated in provocative environments. Similar methodology can be used to parse the neural networks that mediate other complex responses to environmental stimuli.

Figure 1. Locations of Fos-labeled neurons in two animals exhibiting strong symptoms of motion sickness (response type 1) during galvanic vestibular stimulation.

Neuronal locations were plotted on photomontages of sections taken using a 4X objective. Sections (A, E) are from animal C52, whereas (B–D) are from animal C39. The sections were located at the following approximate distances posterior to stereotaxic zero, in accordance with Berman’s atlas : A, 13.5 mm; B, 10 mm; C, 9 mm; D, 7 mm; E, 3 mm. Abbreviations: BC, brachium conjunctivum; CN, cochlear nuclei; DMV, dorsal motor nucleus of the vagus; DRNL, lateral division of dorsal raphe nucleus; DRNM, medial division of dorsal raphe nucleus; EC, external cuneate nucleus; G, genu of facial nerve; IO, inferior olivary nucleus; LRN, lateral reticular nucleus; PBN, parabrachial nucleus; PH, prepositus hypoglossi; RB, restiform body; RM, raphe magnus; RO, raphe obscurus; RP, raphe pallidus; SNV, spinal trigeminal nucleus; STN, subtrigeminal nucleus; STV, spinal trigeminal tract; VI, abducens nucleus; VII, facial nucleus; VIN, inferior vestibular nucleus; VLD, dorsal division of lateral vestibular nucleus; VLV, ventral division of lateral vestibular nucleus; VMN, medial vestibular nucleus; XII, hypoglossal nucleus.

Figure 2. Locations of Fos-labeled neurons in the two unstimulated control animals (C83 and C84).

Neuronal locations were plotted on photomontages of sections taken using a 4X objective. Sections (A, B, E) are from animal C83, whereas (C, D) are from animal C84. The sections were located at the following approximate distances posterior to stereotaxic zero, in accordance with Berman’s atlas: A, 13.5 mm; B, 12 mm; C, 8 mm; D, 6 mm; E, 4 mm. Abbreviations are the same as in Fig. 1, with the following additions: 5M, motor trigeminal nucleus; 5P, principal trigeminal nucleus; LC, locus coeruleus; S, solitary nucleus; SO, superior olivary nucleus; SVN, superior vestibular nucleus.

Figure 3. Photomicrographs of Fos-labeled neurons in a response type 1 animal (C52).

In each row, a rectangular box on the left diagram (generated from photomontages of sections taken using a 4X objective) shows the region depicted at higher magnification to the right. Scale bars on the right photomicrographs designate 500 µm. A, Fos labeling in nucleus tractus solitarius, approximately 13.5 mm posterior to stereotaxic zero. B, Fos labeling in the rostral portion of the medial vestibular nucleus, approximately 6 mm posterior to stereotaxic zero. C, Fos labeling in the periaqueductal gray, approximately 3 mm rostral to stereotaxic zero. Abbreviations are the same as in Figs. 1–2, with the following additions: III, oculomotor nucleus; MR, magnocellular portion of the red nucleus; PAG, periaqueductal gray; SC, superior colliculus.

Figure 4. Photomicrograph illustrating examples of neurons that were immunopositive for Fos (solid black arrows), TPH-2 (solid gray arrows) and both TPH-2 and Fos (open arrow).

A rectangular box on the inset diagram indicates the region of the dorsal raphe nucleus depicted in the photomicrograph. The scale bar represents 250 µm.