Involvement of hormones in olfactory imprinting and homing in chum salmon.

The olfactory hypothesis for salmon imprinting and homing to their natal stream is well known, but the endocrine hormonal control mechanisms of olfactory memory formation in juveniles and retrieval in adults remain unclear. In brains of hatchery-reared underyearling juvenile chum salmon (Oncorhynchus keta), thyrotropin-releasing hormone gene expression increased immediately after release from a hatchery into the natal stream, and the expression of the essential NR1 subunit of the N-methyl-D-aspartate receptor increased during downstream migration. Gene expression of salmon gonadotropin-releasing hormone (sGnRH) and NR1 increased in the adult chum salmon brain during homing from the Bering Sea to the natal hatchery. Thyroid hormone treatment in juveniles enhanced NR1 gene activation, and GnRHa treatment in adults improved stream odour discrimination. Olfactory memory formation during juvenile downstream migration and retrieval during adult homing migration of chum salmon might be controlled by endocrine hormones and could be clarified using NR1 as a molecular marker.

Intra-gastric triacetin alters upper gastrointestinal motility in conscious dogs.

AIM: To examine the effect of intra-gastric triacetin on both upper gastrointestinal motility and proximal gastric tone in conscious dogs. METHODS: Three beagle dogs under sedation were surgically implanted with gastrocutaneous fistula in the gastric body and force transducers in the gastric antrum and duodenum. Beginning at week-2 after insertion, the animals were either fasted for 24 h or fed a liquid meal 2-3 h before the experiment. With the animals fully conscious, a polyethylene bag was inserted into the proximal stomach through the gastrocutaneous fistula, followed by 15 min of air inflation (minimal distending pressure of ＋2 mmHg) and then 20 mL of a low-, mid- or high-concentration triacetin solution (0.5%, 1.0% and 2.0%) or warm water (vehicle control). The proximal stomach receptive volume and gastric antral and duodenal contractions were measured over 10 min. The experiment was repeated twice per week over several months, with each animal receiving at least one infusion of the various triacetin solutions and the vehicle at different times. Intergroup differences were assessed by ANOVA and Bonferroni-Dunn post-hoc testing. RESULTS: Intra-gastric infusion of mid- and high-concentration triacetin induced an increase in the proximal stomach receptive volume, and the average increase induced by the high-concentration at 0-4 min after infusion was significantly greater than that induced by the vehicle control (62.4 ± 9.8 vs 18.4 ± 4.7, P < 0.01). The mid- and high-concentration triacetin also produced a temporary inhibition of the gastric antral contractions at 2 min after infusions; however, only the fasted group showed triacetin-induced antral contractile inhibition that was significantly greater than that in the vehicle control group (P < 0.05). In addition, only the fasted group showed a high-concentration triacetin-induced increase in duodenal contractions at 9-10 min that was significantly different from that in the vehicle control group (P < 0.05). CONCLUSION: Intra-gastric infusion of 1.0%-2.0% triacetin delays gastric emptying by increasing proximal stomach receptive volume, temporarily inhibiting gastric antral contractions and facilitating duodenal contractions.

Intragastric infusion of rikkunshito (kampo) induces proximal stomach relaxation in conscious dogs.

PURPOSE: Abnormal proximal gastric relaxation is one of the causes of functional dyspepsia. The purpose of this study is to use a barostat in conscious dogs to determine the effects of rikkunshito, which is considered to have beneficial effects on functional dyspepsia, on the proximal stomach. METHODS: Eight beagles were used. A gastrocutaneous fistula and force transducers were surgically implanted in the middle corpus and gastric antrum and duodenum, respectively. After a recovery period, a plastic bag was inserted through the gastrocutaneous fistula and the proximal stomach was distended using a barostat. First, four dogs were used to investigate the pressure-volume relation in the fasted and postprandial phases. Second, the stomachs of four different dogs were continuously distended at minimal distending pressure +2 mmHg, and 5 min later were infused with warmed liquid rikkunshito (2 g/20 mL) or water through the gastrocutaneous fistula. Finally, changes in the proximal gastric volume and gastrointestinal motility were observed. RESULTS: The proximal stomach was significantly more pliable in the postprandial phase than in the fasted phase. The proximal gastric volume increased immediately after liquid infusion under constant pressure in both phases and duodenal motility was accelerated. The effect of rikkunshito was significantly greater and lasted longer than that of water. No significant difference between the effects during the fasted or postprandial phase and no change in the gastric antrum motility were observed when rikkunshito was infused. CONCLUSION: These results indicate that rikkunshito accelerates duodenal motility and relaxes the proximal stomach.

Similarities of the neuronal circuit for the induction of fictive vomiting between ferrets and dogs.

Previous studies suggested that the following neuronal circuit participates in the induction of vomiting by afferent vagal stimulation in decerebrated paralyzed dogs: (1) afferent fibers of the vagus nerve, (2) neurons of the solitary nucleus (NTS), (3) neurons of the prodromal sign center near the semicompact part of the nucleus ambiguus (scAMB), (4) neurons of the central pattern generator in the reticular area adjacent to the compact part of nucleus ambiguus (cAMB), (5) respiratory premotor neurons in the caudal medulla, (6) motor neurons of the diaphragm and abdominal muscles. However, the commonality of this neuronal circuit in different species has not yet been clarified. Thus, this study was conducted to clarify this point. This study clarified for the first time that fictive vomiting in decerebrated paralyzed ferrets could be induced by vagal stimulation, and could be identified by centrifugal activity patterns of the phrenic and abdominal muscle nerves. The distributions of c-Fos immunoreactive neurons in the NTS, scAMB and cAMB areas in ferrets that exhibited fictive vomiting were denser than those in ferrets that did not. Application of the nonNMDA receptor antagonist into the 4th ventricle produced the reversible suppression of fictive vomiting. The NK1 receptor immunoreactive puncta were found in the reticular area adjacent to the scAMB. Microinjections of NK1 receptor antagonist into the reticular areas on both sides abolished fictive vomiting. All these results in the ferrets are identical with results previously obtained in dogs and cats. Therefore, this suggests that the above neuronal circuit commonly participates in the induction of emesis in these animal species.

Antro-pancreatic reflexes: long- and short-route reflexes in exocrine and endocrine pancreatic secretion in dogs.

Pancreatic exocrine secretion is known to be facilitated by gastric antral distension via long- and short-route reflexes. In this study, we studied the effects of gastric distension on intra-pancreatic nerve discharges and blood insulin level as well as pancreatic exocrine secretion. Mongrel dogs were anesthetized with ketamine and thiopental, and immediately decerebrated. This study consisted of two series of experiments. In the first series, efferent discharges in an intra-pancreatic nerve branch were recorded, and its responses to antral distension were analyzed. In the second series, effects of antral distension on pancreatic exocrine secretion and blood insulin level were observed before and after vagotomy in splanchnicectomized dogs. Efferent discharges in a pancreatic nerve branch were increased by antral distension. Neither vagotomy nor splanchnicectomy produced obvious changes in the neural response. In splanchnicectomized dogs, antral distension elevated blood insulin level and increased pancreatic exocrine secretion. After subsequent vagotomy, these effects were reduced, but the increases were still greater than 50%. These results indicate that the antro-pancreatic short-route reflex plays a significant role in exocrine secretion, and also suggest that insulin release is increased by antral distension independent of blood glucose level.