Cholecystokinin and bombesin activate neuronatin neurons in the nucleus of the solitary tract.

Neuronatin (Nnat) is involved in the regulation of cellular molecular signaling and appears to be also linked to metabolic processes. The gastrointestinal peptides cholecystokinin (CCK) and bombesin (BN) have an effect on the short-term inhibition of food intake and induce neuronal activation in different brain nuclei, prominently in the nucleus of the solitary tract (NTS) involved in the modulation of food intake. The aim of the study was to examine if Nnat immunoreactivity is detectable in the NTS, and whether peripheral CCK-8S or BN cause c-Fos activation of Nnat neurons. Non-fasted male Sprague-Dawley rats received an intraperitoneal (i.p.) injection of 5.2 or 8.7 nmol CCK-8S/kg or 26 or 32 nmol BN/kg (n = 4 all groups) or vehicle solution (0.15 M NaCl; n = 7). The number of c-Fos neurons was determined 90 min post injection in the NTS and dorsal motor nucleus of the vagus (DMV). We observed Nnat immunoreactive neurons in the NTS and DMV. CCK-8S (25-fold and 51-fold, p = 0.025 and p = 0.001) and BN (31-fold and 59-fold, p = 0.007 and p = 0.001) at both doses increased the number of c-Fos positive neurons in the NTS. CCK and BN did not show a significant effect in the DMV. Both doses of CCK-8S (24-fold and 48-fold p = 0.011 and p = 0.001) and bombesin (31-fold and 56-fold, p = 0.002 and p = 0.001) increased the number of activated Nnat neurons in the NTS (p = 0.001) compared to the vehicle group, while in the DMV no significant increase of c-Fos activation was detected. In conclusion, i.p. injected CCK-8S or BN induce an increased neuronal activity in NTS Nnat neurons, giving rise that Nnat may play a role in the regulation of food intake mediated by peripheral CCK-8S or BN.

Peripheral injection of bombesin induces c-Fos in NUCB2/nesfatin-1 neurons.

As anorexigenic hormones bombesin and nucleobindin2 (NUCB2)/nesfatin-1 decrease food intake in rodents. Both hormones have been described in brain nuclei that play a role in the modulation of hunger and satiety, like the paraventricular nucleus of the hypothalamus (PVN) and the nucleus of the solitary tract (NTS). However, the direct interaction of the two hormones is unknown so far. The aim of study was to elucidate whether bombesin directly interacts with NUCB2/nesfatin-1 neurons in the PVN and NTS. Therefore, we injected bombesin intraperitoneally (ip) at two doses (26 and 32nmol/kg body weight) and assessed c-Fos activation in the PVN, arcuate nucleus (ARC) and NTS compared to vehicle treated rats (0.15M NaCl). We also performed co-localization studies with oxytocin or tyrosine hydroxylase. Bombesin at both doses increased the number of c-Fos positive neurons in the PVN (p<0.05) and NTS (p<0.05) compared to vehicle, while in the ARC no modulation was observed (p>0.05). In the PVN and NTS the number of c-Fos positive neurons colocalized with NUCB2/nesfatin-1 increased after bombesin injection compared to vehicle treatment (p<0.05). Moreover, an increase of activated NUCB2/nesfatin-1 immunoreactive neurons that co-expressed oxytocin in the PVN (p<0.05) or tyrosine hydroxylase in the NTS (p<0.05) was observed compared to vehicle. Our results show that peripherally injected bombesin activates NUCB2/nesfatin-1 neurons in the PVN and NTS giving rise to a possible interaction between bombesin and NUCB2/nesfatin-1 in the modulation of food intake.

The dopamine antagonist flupentixol does not alter ghrelin-induced food intake in rats.

It has been shown that dopamine antagonists suppress the ghrelin-induced increased motivation to work for food. The aim of this study was to investigate the influence of the dopamine antagonist flupentixol on ghrelin-induced food intake. Ad libitum fed male Sprague-Dawley (SD) rats were injected intraperitoneally (ip) with vehicle plus vehicle, vehicle plus ghrelin (13 µg/kg), 0.25mg/kg or 0.5mg/kg flupentixol plus ghrelin, or 0.25mg/kg or 0.5 mg/kg flupentixol plus vehicle. In a second experiment, intracerebroventricularly (icv) cannulated rats received an ip injection of vehicle (0.15M NaCl) or flupentixol (0.25mg/kg) and 20 min later an icv injection of vehicle or ghrelin (1 µg/rat). Both experiments were performed twice: first, rats were offered only standard chow, while in the second experiment they could choose between standard chow and a palatable/preferred chow. Cumulative light phase food intake was assessed for 7h. Ip as well as icv injected ghrelin reliably increased intake of standard chow. Flupentixol did not affect ghrelin-induced intake of standard chow. Ip injected ghrelin failed to increase the intake of palatable chow, whereas icv injected ghrelin did. This effect was not blocked by ip flupentixol. In summary, ip administered ghrelin did not increase the intake of chow the rats preferred; whereas icv injected ghrelin further stimulated the intake of preferred chow suggesting a direct central mediation of this effect. Our results show that the dopamine antagonist flupentixol does not influence ghrelin-induced feeding in our choice paradigm.

Peripheral injected cholecystokinin-8S modulates the concentration of serotonin in nerve fibers of the rat brainstem.

Serotonin and cholecystokinin (CCK) play a role in the short-term inhibition of food intake. It is known that peripheral injection of CCK increases c-Fos-immunoreactivity (Fos-IR) in the nucleus of the solitary tract (NTS) in rats, and injection of the serotonin antagonist ondansetron decreases the number of c-Fos-IR cells in the NTS. This supports the idea of serotonin contributing to the effects of CCK. The aim of the present study was to elucidate whether peripherally injected CCK-8S modulates the concentration of serotonin in brain feeding-regulatory nuclei. Ad libitum fed male Sprague-Dawley rats received 5.2 and 8.7 nmol/kg CCK-8S (n=3/group) or 0.15M NaCl (n=3-5/group) injected intraperitoneally (ip). The number of c-Fos-IR neurons, and the fluorescence intensity of serotonin in nerve fibers were assessed in the paraventricular nucleus (PVN), arcuate nucleus (ARC), NTS and dorsal motor nucleus of the vagus (DMV). CCK-8S increased the number of c-Fos-ir neurons in the NTS (mean±SEM: 72±4, and 112±5 neurons/section, respectively) compared to vehicle-treated rats (7±2 neurons/section, P<0.05), but did not modulate c-Fos expression in the DMV or ARC. Additionally, CCK-8S dose-dependently increased the number of c-Fos-positive neurons in the PVN (218±15 and 128±14, respectively vs. 19±5, P<0.05). In the NTS and DMV we observed a decrease of serotonin-immunoreactivity 90 min after injection of CCK-8S (46±2 and 49±8 pixel/section, respectively) compared to vehicle (81±8 pixel/section, P<0.05). No changes of serotonin-immunoreactivity were observed in the PVN and ARC. Our results suggest that serotonin is involved in the mediation of CCK-8's effects in the brainstem.