Distribution of cholecystokinin receptors in the bovine brain: a quantitative autoradiographic study

Microarray analysis of differentially expressed genes in the brains of tubby mice

The tubby mouse is characterized by progressive retinal and cochlear degeneration and late-onset obesity. These phenotypes are caused by a loss-of-function mutation in the tub gene and are shared with several human syndromes, suggesting the importance of tubby protein in central nervous system (CNS) functioning. Although evidence suggests that tubby may act as a transcription factor mediating G-protein coupled receptor (GPCR) signaling, any downstream gene regulated by tubby has yet to be identified. To explore potential target genes of tubby with region-specific transcription patterns in the brain, we performed a microarray analysis using the cerebral cortex and hypothalamus of tubby mice. We also validated the changes of gene expression level observed with the microarray analysis using real-time RT-PCR. We found that expression of erythroid differentiation factor 1 (Erdr1) and caspase 1 (Casp1) increased, while p21-activated kinase 1 (Pak1) and cholecystokinin 2 receptor (Cck2r) expression decreased in the cerebral cortex of tubby mice. In the hypothalamic region, Casp 1 was up-regulated and micro-crystallin (CRYM) was down-regulated. Based on the reported functions of the differentially expressed genes, these individual or grouped genes may account for the phenotype of tubby mice. We discussed how altered expression of genes in tubby mice might be understood as the underlying mechanism behind tubby phenotypes.

Wiring and volume transmission in rat amygdala. Implications for fear and anxiety

The amygdala plays a key role in anxiety. Information from the environment reaches the amygdaloid basolateral nucleus and after its processing is relayed to the amygdaloid central nucleus where a proper anxiogenic response is implemented. Experimental evidence indicates that in this information transfer a GABAergic interface controls the trafficking of impulses between the two nuclei. Recent work indicates that interneuronal communication can take place by classical synaptic transmission (wiring transmission) and by volume transmission in which the neurotransmitter diffuses and flows through the extracellular space from its site of release and binds to extrasynaptic receptors at various distances from the source. Based on evidence from our laboratory the concept is introduced that neurotransmitters in the amygdala can modulate anxiety involving changes in fear learning and memories by effects on receptor mosaics in the fear circuits through wiring and volume transmission modes of communication.

Role of the amygdaloid cholecystokinin (CCK)/gastrin-2 receptors and terminal networks in the modulation of anxiety in the rat. Effects of CCK-4 and CCK-8S on anxiety-like behaviour and [3H]GABA release

The amygdala plays a key role in fear and anxiety. The intercalated islands are clusters of glutamate-responsive GABAergic neurons rich in cholecystokinin (CCK)-2 receptors which control the trafficking of nerve impulses from the cerebral cortex to the central nucleus of amygdala. In this study, the nature of the CCK-glutamate-GABA interactions within the rat rostral amygdala, and their relevance for anxiety, were studied. CCK/gastrin-like immunoreactive nerve terminals were found to be mainly restricted to the paracapsular intercalated islands and the rostrolateral part of the main intercalated island. Behaviourally, the bilateral microinjection of CCK-4 (0.043-4.3 pmol/side) or CCK-8S (4.3 pmol/side) into the rostrolateral amygdala reduced the open-arm exploration in the elevated plus-maze without affecting locomotion. In contrast, neither CCK-4 nor CCK-8S (0.043-4.3 pmol/side) had any effects in the shock-probe burying test as compared with their saline-treated controls. Biochemically, CCK-4 (0.3 and 1.5 microm), unlike CCK-8S, enhanced significantly the K(+)-stimulated release of [(3)H]GABA from amygdala slices. These effects were fully prevented by prior superfusion of the slices with either the selective CCK-2 receptor antagonist CR2945 (3 microm), or 6,7-dinitroquinoxaline-2,3(1H,4H)-dione (DNQX), 10 microm, a glutamatergic (+/-)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA)/kainate receptor antagonist. It is suggested that CCK modulates glutamate-GABA mechanisms by acting on CCK-2 receptors via volume transmission occurring at the level of the basolateral amygdaloid nucleus and/or by synaptic or perisynaptic volume transmission in the region of the rostrolateral main and paracapsular intercalated islands, resulting in subsequent disinhibition of the central amygdaloid nucleus and anxiety or panic-like behaviour.

Differential tissular expression of the CCK(A) and CCK(B) gastrin receptor genes during postnatal development in the calf

Local and temporal expression of CCK(A) and CCK(B)/gastrin receptor genes was studied in the calf with a quantitative Reverse Transcription-Polymerase Chain Reaction (RT-PCR) method. Cerebral cortex, antrum, fundus, gall bladder, pancreas and liver were analyzed in calves at 0, 2, 7, 21, 28 and 150 days of age. Cerebral cortex and pancreas expressed both receptor genes with a ratio between CCK(A) and CCK(B)/gastrin receptor transcripts varying according to the age. Gall bladder and fundus showed an exclusive expression of CCK(A) and CCK(B)/gastrin receptor mRNAs, respectively, with the highest levels of transcripts in newborn and 28-day-old calves. The rank order for CCK(A) receptor mRNA expression was gall bladder > pancreas > cerebral cortex >>> antrum and that for CCK(B)/gastrin receptor mRNA expression was cerebral cortex / pancreas / fundus >> antrum. No CCK(A) and CCK(B)/gastrin receptor mRNA was detected in liver, regardless of the age of calves. The present data represent a basis for a better understanding of the ontogeny of physiological functions linked to the CCK(A) and CCK(B)/gastrin receptors.

Electrical stimulation of the prefrontal cortex increases cholecystokinin, glutamate, and dopamine release in the nucleus accumbens: an in vivo microdialysis study in freely moving rats

In vivo microdialysis, radioimmunoassay, and HPLC with electrochemical or fluorometric detection were used to investigate the release of cholecystokinin (CCK), glutamate (Glu), and dopamine (DA) in nucleus accumbens septi (NAS) as a function of ipsilateral electrical stimulation of medial prefrontal cortex (mPFC). CCK was progressively elevated by mPFC stimulation at 50-200 Hz. Stimulation-induced CCK release was intensity-dependent at 250-700 microA. NAS Glu and DA levels were each elevated by stimulation at 25-400 Hz; the dopamine metabolites DOPAC and homovanillic acid were increased by stimulation at 100-400 Hz. When rats were trained to lever press for mPFC stimulation, the stimulation induced similar elevations of each of the three transmitters to those seen with experimenter-administered stimulation. Perfusion of 1 mM kynurenic acid (Kyn) into either the ventral tegmental area (VTA) or NAS blocked lever pressing for mPFC stimulation. VTA, but not NAS, perfusion of Kyn significantly attenuated the increases in NAS DA levels induced by mPFC stimulation. Kyn did not affect NAS CCK or Glu levels when perfused into either the VTA or NAS. The present results are consistent with histochemical evidence and provide the first in vivo evidence for the existence of a releasable pool of CCK in the NAS originating from the mPFC. Although dopamine is the transmitter most closely linked to reward function, it was CCK that showed frequency-dependent differences in release corresponding most closely to rewarding efficacy of the stimulation. Although not essential for the reward signal itself, coreleased CCK may modulate the impact of the glutamatergic action in this behavior.

Food for thought: a critique on the hypothesis that endogenous cholecystokinin acts as a physiological satiety factor

This review evaluates the various lines of evidence supporting the hypothesis that cholecystokinin (CCK) released from the small intestine during feeding plays a physiological satiety. Issues considered include, the effects of systemic injection of CCK on consummatory and operant feeding, the role of the vagus nerve, the effects of CCKB receptor antagonists, and the neuroendocrine responses to exogenous CCK. A critical appraisal of this research indicates that while it is clearly demonstratable that exogenous peripheral CCK can alter food intake by acting on CCKA receptors, the mechanism involved may be more closely related to the induction if aversion and nausea, rather than satiety. With regard to peripheral endogenous CCK, the available evidence also does not seem to support a role for the hormone in satiety. In particular, it is doubtful whether plasma concentrations of CCK following a meal are sufficiently high to inhibit feeding. Moreover, CCKA receptor antagonist which do not cross the blood brain barrier fail to increase meal size, as would be expected if peripheral CCK was an effective satiety factor. In addition, the recent literature concerned with the possibility that CCK may have a direct action within the brain in the control of food intake has been reviewed. These studies show that CCK administered intracerebroventicularly, or by micoinjection into discrete brain regions, also inhibits feeding via a CCKA receptor mechanism. However, the physiological relevance of these findings have yet to be determined.

Effect of local cholecystokinin-8 administration on extracellular levels of amino acids and glycolytic products monitored by in vivo microdialysis in the fronto-parietal cortex of the rat

The effects of local cholecystokinin-8 (CCK-8) administration on cortical extracellular levels of amino acids, catecholamines and metabolism products were studied in the halothane anaesthetized rat by in vivo microdialysis. CCK-8 (10 microM), administrated via a microdialysis probe, produced a significant increase in the levels of aspartate, glutamate and gamma-aminobutyric acid (GABA), but not of 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), lactate and pyruvate, which were simultaneously monitored. The increase in aspartate and glutamate levels produced by CCK-8 was about 3-4-fold. The effect of CCK-8 on aspartate levels was significantly inhibited by the CCKB antagonist, L-365,260 (20 mg kg-1, s.c.), but not by the CCKA antagonist, L-364,718 (20 mg kg-1, s.c.). In contrast, the increase in glutamate levels was inhibited by both L-365,260 and L-364,718. GABA was slightly, but significantly increased (approximately 30%), by local CCK-8 and was inhibited by both CCK antagonists. The present results show that CCK-8 exerts a strong modulatory action on both aspartate and glutamate release in rat cortex. While the effect of CCK-8 on aspartate is selectively mediated via CCKB receptor subtype, the effect of CCK-8 on glutamate appears to be mediated via both CCKA and CCKB receptor subtypes.