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

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. © 2014 Balaban et al

The effects of ibuprofen and the neurokinin-1 receptor antagonist GR205171A on Fos expression in the ferret trigeminal nucleus following tooth pulp stimulation.

We have developed a model to study central changes following inflammation of the tooth pulp in the ferret and have examined Fos expression in the trigeminal nucleus following stimulation of non-inflamed and inflamed tooth pulps. The aim of this study was to establish the ability of this model to predict analgesic efficacy in clinical studies of inflammatory pain. We addressed this by assessing the effects of the neurokinin-1 receptor antagonist GR205171A and ibuprofen on Fos expression following stimulation of the inflamed pulp and comparing this with known analgesic efficacy. Adult ferrets were prepared under anaesthesia to allow tooth pulp stimulation, recording from the digastric muscle and intravenous injections at a subsequent experiment. In some animals pulpal inflammation was induced, by introducing human caries into a deep buccal cavity. After 5 days, animals were reanaesthetised, treated with vehicle, GR205171A or ibuprofen and the teeth were stimulated at ten times the threshold of the jaw-opening reflex. Stimulation of all tooth pulps induced ipsilateral Fos in trigeminal subnuclei caudalis and oralis. GR205171A had no significant effect on Fos expression in the trigeminal nucleus of animals with either non-inflamed or inflamed tooth pulps. Ibuprofen reduced Fos expression in the trigeminal nucleus and this effect was most marked in animals with pulpal inflammation. These results differ from those previously described using a range of other animal models, but agree with known clinical efficacy of neurokinin-1 receptor antagonists and ibuprofen. Therefore this model is likely to be of use in accurately predicting the analgesic efficacy of novel compounds

The 5-HT(3) receptor antagonist alosetron inhibits the colorectal distention induced depressor response and spinal c-fos expression in the anaesthetised rat.

BACKGROUND: Noxious intestinal distention elicits a reflex depressor response in the sodium pentobarbitone anaesthetised rat, which can be used as an index of visceral nociception. 5-HT(3) receptor antagonists inhibit this reflex. Repeated colorectal distention (CRD) induces Fos like immunoreactivity (Fos-LI) in the rat spinal cord. AIMS: To examine the effect of the 5-HT(3) receptor antagonist alosetron on the depressor response to CRD, and on Fos expression in the lumbosacral spinal cord. METHODS: Male rats were anaesthetised with sodium pentobarbitone, and mean arterial blood pressure monitored during repeated colorectal balloon inflation before and after treatment with alosetron or saline. Rats anaesthetised with urethane and treated with alosetron or saline underwent a repeated CRD paradigm, after which the lumbosacral spinal cord was removed and processed for visualisation of Fos-LI. RESULTS: CRD elicited reproducible, volume dependent falls in arterial blood pressure, and repeated distention-effect curves were constructed. Alosetron (1-100 microg/kg intravenously) inhibited the depressor response to CRD in a dose related manner, with an ID(50) value of 3.0 microg/kg. Following repeated CRD, numbers of Fos-LI neurones were significantly increased to 1246 (total in 12 sections at 120 microm intervals from L6 to S1) compared with 49 in sham distended animals. Pretreatment with alosetron (100 microg/kg) significantly reduced numbers of Fos-LI neurones to 479.8. CONCLUSION: The 5-HT(3) receptor antagonist alosetron inhibits the depressor response to CRD in a potent and dose dependent manner. It also inhibits CRD induced Fos-LI in the spinal cord. These results suggest that 5-HT(3) receptors are involved in visceral nociceptive transmission, perhaps located on primary afferent or spinal neurones

nNOS expression following inferior alveolar nerve injury in the ferret.

Damage to the inferior alveolar nerve (IAN) may result in permanent painful dysaesthesia, and there is compelling evidence to suggest that ectopic activity from the injury site plays a crucial role in the initiation of this disorder. The aim of this study was to determine whether neuronal nitric oxide synthase (nNOS), a regulator of neuronal excitability, could be involved in the development of the abnormal activity. In seven ferrets, the left IAN was exposed and a retrograde tracer, fluorogold, was applied to the nerve for the identification of cell bodies in the trigeminal ganglion with axons in the IAN. In four animals, the nerve was sectioned distal to the injection site, and three served as controls. After 3 days, the animals were perfused with fixative, and the left and right IANs and trigeminal ganglia were processed using indirect immunofluorescence for nNOS. Image analysis was used to quantify the percentage area of staining (PAS) at the injury site. In the ganglia, counts were made of positively labelled cells in the fluorogold population. At the injury site, PAS was significantly greater in injured nerves than in either contralateral or control nerves, and contralateral PAS was elevated compared to control. In the ganglia, the proportion of nNOS-labelled cells was significantly reduced following injury. These results indicate a possible translocation of the nNOS protein from the cell body to the site of nerve injury, where it accumulates. Thus, nNOS could play a role in the development of ectopic activity at a site of trigeminal nerve injury