Disruptions in feeding and body weight control in gastrin-releasing peptide receptor deficient mice

Bombesin (BN) interacts with two mammalian receptor subtypes termed gastrin-releasing peptide (GRP)-preferring (GRP-R) and neuromedin B (NMB)-preferring (NMB-R) that may mediate the satiety action of BN. We examined the feeding behavior of mice that were deficient in the GRP-R (GRP-R KO) to assess the overall contribution of this receptor subtype in the feeding actions of BN-related peptides. GRP-R KO mice failed to suppress glucose intake in response to systemically administered BN and GRP(18-27), whereas both peptides elicited a potent reduction of intake in wild-type (WT) mice. Neither GRP-R KO nor WT mice suppressed glucose intake following NMB administration. Unlike the impaired responses to BN-like peptides, the feeding inhibitory action of cholecystokinin was enhanced in GRP-R KO mice. Consistent with behavioral results, GRP-R KO mice also exhibited a reduction in c-Fos immunoreactivity in the nucleus of the solitary tract (NTS) and paraventricular nucleus (PVN) following peripheral administration of BN. An evaluation of meal patterns showed that GRP-R KO mice ate significantly more at each meal than WT mice, although total 24 h food consumption was equivalent. A long-term analysis of body weight revealed a significant elevation in GRP-R KO mice compared with WT littermates beginning at 45 weeks of age. These data suggest that the GRP-R mediates the feeding effects of BN-like peptides and participates in the termination of meals in mice.

Role of endogenous CCK in the inhibition of gastric emptying by peptone and Intralipid in rats

To assess the role of endogenous cholecystokinin in the control of gastric emptying of peptone solutions and Intralipid suspensions, we examined the ability of a dose range of the CCK-A antagonist, devazepide to accelerate the gastric emptying of various caloric concentrations of peptone and Intralipid in rats. In the absence of devazepide, both peptone and Intralipid emptying slowed with increasing concentration. Devazepide's effect on peptone gastric emptying diminished with increasing peptone concentration. The threshold dose for accelerating the emptying of 0.2 kcal/ml peptone was lower than the threshold dose for affecting 0.5 kcal/ml peptone and devazepide had no effect on the gastric emptying of 1.0 kcal/ml peptone. In contrast, devazepide affected Intralipid gastric emptying at all three Intralipid concentrations and the threshold dose decreased with increasing Intralipid concentration. However, the magnitude of the effect of devazepide on peptone or Intralipid gastric emptying was partial and did not increase as a function of concentration. These data demonstrate a role for endogenous CCK in the emptying of peptone and Intralipid but suggest that endogenous CCK does not account for the increased slowing of gastric emptying evident with increased caloric concentration.

Inhibition of gastric emptying by bombesin-like peptides is dependent upon cholecystokinin-A receptor activation

The amphibian peptide bombesin (BN) and the related mammalian peptides gastrin-releasing peptide (GRP) and neuromedin B (NMB) inhibit gastric emptying in rats. Exogenous administration of BN stimulates the release of cholecystokinin (CCK), a gastrointestinal peptide that also potently inhibits gastric emptying. To determine whether the inhibition of gastric emptying by BN-like peptides is mediated by a CCK-dependent mechanism, we examined the ability of the CCK-A receptor antagonist, devazepide, to block the inhibition of saline gastric emptying produced by BN, GRP18-27 and NMB. Using the same dosages as in the gastric emptying experiment, we also evaluated the effect of devazepide on feeding suppression produced by systemically administered BN. Our results showed that devazepide completely blocked the suppression of gastric emptying produced by BN, GRP18-27 and NMB but had no effect on BN-induced suppression of food intake. These results suggest that BN-like peptides inhibit gastric emptying through an indirect mechanism that is dependent upon CCK-A receptor activation. In contrast, the suppression of food intake by BN, in this experimental paradigm, is independent of CCK-A receptors.

Identification of Src as a novel atypical protein kinase C-interacting protein

Atypical protein kinase C-zeta (PKC-zeta) participates in nerve growth factor (NGF) signaling and is required for NGF-induced differentiation of PC12 cells. The biological activity of PKC-zeta is likely mediated by interaction of PKC-zeta with specific proteins. Affinity column chromatography employing the PKC-zeta regulatory domain coupled to glutathione-agarose was used to search for proteins that bound PKC-zeta. Two proteins (59/60 kDa) were recovered from NGF-stimulated PC12 cell lysates that bound the matrix. Western blot analysis of pooled column fractions identified these proteins as tubulin and src, respectively. Using purified preparations of src and tubulin, PKC-zeta was shown to interact with both proteins using blot overlay. To demonstrate a functional interaction in vivo, PC12 cells expressing a temperature-sensitive v-src were shifted to the permissive temperature (37 degrees C), followed by immunoprecipitation. At the permissive temperature where src was active, PKC-zeta was tyrosine phosphorylated and coassociated with src in vivo; by comparison, at the nonpermissive temperature (40 degrees C) PKC-zeta was not tyrosine phosphorylated. Taken together, these findings support a novel role for the interaction of src and atypical PKC in vivo, which is dependent upon the activity of src and the tyrosine phosphorylation state of PKC-zeta.

Relationships between gastric motility and gastric vagal afferent responses to CCK and GRP in rats differ

The brain-gut peptides cholecystokinin (CCK) and the mammalian bombesin-like peptide gastrin-releasing peptide (GRP) suppress food intake. Vagotomy blocks CCK- but not bombesin (BN)-induced feeding suppression, demonstrating differential vagal contributions. We examined the relationship between the ability of CCK and the active fragment of GRP, GRP-(18-27), to stimulate gastric vagal afferent activity and their ability to elicit changes in gastric motility. We also examined ligated cervical vagal segments and revealed specific 125I-CCK vagal binding without evidence of radiolabeled BN binding sites. Both close arterial and intraperitoneal CCK and GRP-(18-27) produced dose-dependent increases in activity in gastric vagal mechanoreceptive afferents. CCK dose dependently decreased gastric pressure without altering antral wall tension, whereas GRP-(18-27) dose dependently increased both gastric pressure and peak antral wall muscle tension. These results suggest that GRP-(18-27) activates gastric vagal afferents secondary to its stimulation of gastric motor effects. CCK activates this same population of vagal afferents independent of changes in gastric tension, suggesting a direct action of CCK at functional vagal CCK receptors.