Neuronal expression of Fos protein in the paraventricular nucleus of the hypothalamus after i.p. injection of ulcergenic cinchophen

Vagal afferent signaling of a gastric mucosal acid insult to medullary, pontine, thalamic, hypothalamic and limbic, but not cortical, nuclei of the rat brain

Although gastric acid is a factor in upper abdominal pain, the signaling and processing of a gastric mucosal acid insult within the brain are not known. This study examined which nuclei in the rat brain respond to challenge of the gastric mucosa by a noxious concentration of hydrochloric acid (HCl) and whether the central input is carried by vagal afferent neurons. Activation of neurons in the brain was mapped by in situ hybridization autoradiography of messenger ribonucleic acid (mRNA) for the immediate early gene c-fos 45 min after intragastric administration of saline or HCl. Following intragastric HCl (0.5 M) challenge, many neurons in the nucleus tractus solitarii, lateral parabrachial nucleus, thalamic and hypothalamic paraventricular nucleus, supraoptic nucleus, central amygdala and medial/lateral habenula expressed c-fos mRNA as compared to intragastric treatment with saline (0.15 M). However, c-fos transcription in the insular cortex was not enhanced by the gastric acid insult. Hypertonic saline (0.5 M) caused only a minor expression of c-fos mRNA in the hypothalamus and amygdala. The acid-evoked c-fos induction in subcortical nuclei was depressed by at least 80% five days after bilateral subdiaphragmatic vagotomy. Collectively, these observations indicate that vagal afferent input from the acid-threatened gastric mucosa does not reach the insular cortex but leads to activation of subcortical brain nuclei that are involved in emotional, behavioral, neuroendocrine, autonomic and antinociceptive reactions to a noxious stimulus.

Gastric acid-evoked c-fos messenger RNA expression in rat brainstem is signaled by capsaicin-resistant vagal afferents

BACKGROUND & AIMS

Gastric acid is known to contribute to ulcer pain, but the mechanisms of gastric chemonociception are poorly understood. This study set out to investigate the pathways and mechanisms by which gastric acid challenge is signaled to the brain.

METHODS

Neuronal excitation in the rat brainstem and spinal cord after intragastric administration of HCl (0.35-0.7 mol/L) was examined by in situ hybridization autoradiography for the immediate early gene c-fos.

RESULTS

Gastric acid challenge did not induce c-fos transcription in the spinal cord but caused many neurons in the nucleus tractus solitarii and area postrema to express c-fos messenger RNA (mRNA). The HCl concentration-dependent excitation of medullary neurons was in part associated with behavioral manifestations of pain but not directly related to the acid-induced injury and contraction of the stomach. Subdiaphragmatic vagotomy suppressed the c-fos mRNA response to intragastric acid, and morphine inhibited it in a naloxone-reversible manner, whereas pretreatment of rats with capsaicin was without effect.

CONCLUSIONS

Gastric acid challenge is signaled to the brainstem, but not the spinal cord, through vagal afferents that are sensitive to acid but resistant to capsaicin. It is hypothesized that the gastric acid-induced c-fos transcription in the brainstem is related to gastric chemonociception.

Neuronal expression of FOS protein in the nucleus tractus solitarii and the dorsal motor nucleus of the vagus nerve after i.p. injection of ulcerogenic aspirin

Aspirin, a common analgesic-antipyretic and anti-inflammatory drug, often induces gastric ulcer, but its pathogenesis remains unsettled. The purpose of this study was to identify the CNS neurons that express FOS protein after i.p. injection of aspirin (100-300 mg/kg). This was done in the unanesthetized Wistar rats with careful physiological controls. Dose-dependently, many FOS-immunoreactive (FOS-ir) neurons were found in the medial part of the nucleus tractus solitarii (NTSm) and the dorsal motor nucleus of the vagus nerve (DMX) of the lower medulla, but none in the paraventricular nucleus of the hypothalamus (PVH). Distribution of FOS-ir neurons in the DMX corresponds with that of the visceromotor neurons involved in gastric secretion. This study suggests that the aspirin-induced gastric ulcer may not originate in the PVH but in the NTSm-DMX system.

The comparison of effects of various anesthetics on expression of Fos protein in the rat brain

The purpose of this study was to compare effects of various anesthetic drugs on expression of Fos protein in the supraspinal neurons of rats. Optimum anesthesia was maintained under monitoring of EEG. Degree of Fos expression was evaluated by counts of Fos-immunoreactive (ir) neurons. Urethane induced the largest amount of Fos-ir neurons (n = 8439), while fentanyl/midazolam the smallest (n = 112). alpha-Chloralose, halothane, pentobarbital sodium and urethane/alpha-chloralose induced amounts in between. The results indicate that fentanyl/midazolam is the most recommendable anesthetic drug in the Fos expression study.