Possible involvement of the CCK receptor in the benzodiazepine antagonism to CCK in the mouse brain

Differential cholecystokinin brain/gut transcription initiation in the rat: evidence for brain-specific start sites

Brain/gut cholecystokinin (CCK) has well-established translational and post-translational differences. By contrast, CCK transcription regulation is reported to be the same in brain and gut. Accordingly, the rat CCK gene has been evaluated for differential brain/gut transcription initiation. Using the 5'-flanking region of the rat CCK gene, DNase I protection assays were performed. We evaluated reporter constructs deleted of the conventional transcription start site in cell culture. Finally, brain and gut mRNA was evaluated using both a reverse transcription serial primer polymerase chain reaction assay as well as rapid amplification of cDNA ends (RACE) analysis. TFIID protein protects against DNase I digestion between -177 and -196 bp. In tissue culture, spontaneous 5'-flanking region transcription initiation occurs until deletion proceeds upstream of -140 bp. RACE analysis performed on mRNA from the rat brain identifies heretofore undescribed transcription initiation at -43 bp 5' as well as at +1,212 (in exon II). These alternative transcription initiation sites are utilized in brain, but not gut. The rat CCK gene has alternative 5'-flanking region transcription initiation sites. These alternative sites are utilized only in the brain. These data may provide insights into how brain and gut respond to their differing physiological demands.

The benzodiazepine antagonist flumazenil blocks the effects of CCK receptor agonists and antagonists in the elevated plus-maze

Peripheral administration of the unsulphated cholecystokinin octapeptide (CCK-8us) led to an anxiogenic-like action in the elevated plus-maze model of anxiety in rats. Devazepide and L-365,260 showed potent anxiolytic-like effects at similar doses. The fact that devazepide is 1000 times more potent as a CCK-A receptor antagonist than L-365,260, whereas the two compounds are nearly equipotent at the CCK-B receptor subtype, suggests that CCK-B rather than CCK-A receptors are involved in these effects. Similar results were obtained in mice using the two-compartment test. In the elevated plus-maze, the benzodiazepine antagonist, flumazenil, which was inactive when given alone, significantly antagonized the anxiogenic-like activity of CCK-8us and the anxiolytic-like effects of devazepide and L-365,260. These results suggest a complex interaction between benzodiazepine and CCK receptor mechanisms in the regulation of anxiety states.

The CCK-A and CCK-B receptor antagonists, devazepide and L-365,260, enhance morphine antinociception only in non-acclimated rats exposed to a novel environment

Devazepide, a potent CCK-A receptor antagonist, and L-365,260, a selective CCK-B receptor antagonist, have been introduced as pharmacologic tools for differentiating the physiologic roles of CCK-A and CCK-B receptor subtypes. In the present study, we tested the effects of devazepide and L-365,260, on morphine antinociception in rats using the thermal sensorimotor tail flick test. Both devazepide and L-365,260 significantly enhanced the antinociceptive action of morphine, but only in rats that had not been acclimated to the laboratory environment or habituated to investigator handling. When tested with fully acclimated animals, devazepide and L-365,260 had no effect whatsoever; they neither enhanced nor attenuated morphine-induced antinociception. These observations indicate that the effects of devazepide and L-365,260, CCK antagonists, on morphine antinociception appear to be dependent on the animal's response to a new environment or to the stress induced by an unaccustomed experimental paradigm.

Interaction of cholecystokinin and diazepam: effects on brain monoamines

An antagonism between cholecystokinin (CCK) peptides and benzodiazepines (BZD) has been described in various paradigms. We sought to determine whether CCK and BZD are also antagonistic in their effects on brain neurotransmitter levels in the rat. No effect on the noradrenergic system was induced in any brain area by CCK 8 S and diazepam alone or in combination. Administered alone, sulfated CCK octapeptide (CCK 8 S) (5 micrograms/kg ip) and diazepam (5 mg/kg ip) were found to decrease DOPAC levels in the cortex and to induce 5-hydroxy-tryptamine accumulation in the hippocampus. When administered together, these variations were no longer observed. However, a slight tendency by each substance to decrease 3-methoxy-tyramine levels in the striatum, became significant when given in association. The differences in CCK-BZD interactions observed in the striatum, cortex and hippocampus suggest that different mechanisms of action are involved. The addition of the effects occurring in the striatum might involve a GABA-ergic mechanism.

Differential cholecystokinin gene expression in brain and gut of the fasted rat

Cholecystokinin (CCK) gene expression has been compared in the brain and duodenum of control and 5 days fasted rats. To study transcription, CCK mRNA was quantified using a solution hybridization assay. Large and small molecular weight CCK peptides were separated using a sequential extraction process and subsequently quantified by radioimmunoassay. In the duodenum, a fall in weight was paralleled by a decrease in CCK mRNA and in the large forms of CCK peptides. Small molecular species of CCK peptides did not change. There was no change in weight, CCK transcriptional or translational products in the brain as a whole. These data indicate location-specific differential regulation of the products of CCK gene expression in the fasted rat.

Appetite-modulating drugs in dwarf goats, with special emphasis on benzodiazepine-induced hyperphagia and its antagonism by flumazenil and RO 15-3505

In dwarf goats fasted for 2 h, i.v. administration of the benzodiazepine (BZ) agonists diazepam (60 micrograms/kg), brotizolam (2 and 4 micrograms/kg) and climazolam (100 micrograms/kg) induced hyperphagic effects, whereas i.v. injections of the BZ-antagonist flumazenil (R degrees 15-1788; 0.5 mg/kg), the anthelmintic ivermectin (0.1 mg/kg), the 5-HT2 antagonist ritanserine (0.1 mg/kg), ACTH (10 micrograms/kg) and prednisolone (1 mg/kg) were inactive in a 30-min feeding test. Both the BZ-antagonist R degrees 15-3505 (greater than or equal to 0.1 mg/kg) and the opiate receptor antagonist naloxone (0.1 mg/kg) had anorectic effects in dwarf goats given 30 min access to a palatable pelleted concentrate. The hyperphagic effects of climazolam and brotizolam were not antagonized by flumazenil, whereas similar doses of this drug completely reversed muscle incoordination and ataxia induced by much higher doses of these BZ-agonists. In the combination experiments with naloxone and BZ-agonists, naloxone antagonized the hyperphagic effects of both diazepam and brotizolam. Similarly, in the diazepam-R degrees 15-3505 study, there was a significant effect of diazepam and a significant inhibition of this effect by R degrees 15-3505 (50 micrograms/kg). In the diazepam-ivermectin combination experiment no evidence for drug potentiation was found. These results and the mode of action of the above mentioned drugs are discussed in relation to feeding behaviour.

Cholecystokinin antagonism by anthramycin, a benzodiazepine antibiotic, in the central nervous system in mice

Anthramycin (ATM) which is a product of some streptomyces micro-organisms was shown to antagonize the central effects of cholecystokinin (CCK) such as antinociception and satiety and to displace CCK bound to the slices from the brains of mice. Sulfated octapeptide CCK (CCK8) was administered intracisternally to mice at doses of 1 microgram/mouse for inducing antinociception and 200 ng/mouse for satiety. ATM was administered intraperitoneally to mice at doses such as 0.3 and 0.5 mg/kg. CCK8-induced antinociception and satiety were significantly reversed by ATM in those doses. [125I]CCK8 binding to the brain slices was observed autoradiographically. The autoradiograms from the slices were converted to false color images by using a microcomputer. The radioactivity in the autoradiograms was expressed by color spectra in the false color images. Comparison of the binding of [125I]CCK8 to the brain slices in the presence and the absence of ATM revealed that ATM (10(-6) M) clearly displaced the CCK8 binding in the various regions, especially in the cortex, of the brain. These findings suggest that ATM acts as an potent antagonist of CCK in the central nervous system in mice.