Regional activation in the rat brain during visceral stimulation detected by c-fos expression and fMRI.

AIM: The aim of the study was to determine and compare the areas of brain activated in response to colorectal distention (CRD) using functional magnetic resonance imaging (fMRI) and c-fos protein expression. METHODS: For fMRI study (3.0 T magnet), anaesthetized rats underwent phasic CRD, synchronized with fMRI acquisition. Stimulation consisted of eight cycles of balloon deflation (90 s) and inflation (30 s), at 40, 60 or 80 mmHg of pressure. For c-fos study two sets of experiments were performed on anaesthetized rats: comparing (A) brain activation in rats with the inserted colorectal balloon (n = 5), to the rats without the balloon (n = 5); and (B) rats with inserted balloon (n = 10), to the rats with inserted and distended balloon (n = 10). The pressure of 80 mmHg was applied for 2 h of 30 s inflation and 90 s deflation, alternating cycles. RESULTS: Functional MRI revealed significant activation in the amygdala, hypothalamus, thalamus, cerebellum and hippocampus. Significant increase in c-fos expression was observed in amygdala and thalamus in the first set of experiments, and hypothalamus and parabrachial nuclei in the second. CONCLUSION: The two methods are not interchangeable but appeared to be complementary: fMRI was more sensitive, whereas c-fos had much greater resolution.

Nitric oxide synthase (NOS) expression in the myenteric plexus of streptozotocin-diabetic rats.

Nitric oxide (NO) is an important inhibitory neurotransmitter in the gut. Alterations in NO mediated responses have been described in diabetic animals. The presence of nitric oxide synthase (NOS) reflects the potential for NO synthesis and is found in neurons in the myenteric plexus. The aim of this study was to determine changes in nitric oxide synthase (NOS) expression in the myenteric plexus of the gastrointestinal tract of diabetic rats at three months of streptozotocin-induced diabetes, compared to age matched controls, using immunohistochemistry. Diabetic animals showed a decrease in NOS expression in the antrum, with 59.1 +/- 7.3% of neurons being positive for NOS in diabetes compared to 81.2 +/- 4.7% in controls (P < 0.05). NOS expression in duodenum, ileum, and colon of diabetic animals was not statistically different from controls. Decreased expression of NOS in antrum may contribute to altered gastric emptying observed in diabetics.