Increased spinal cholecystokinin activity after systemic resiniferatoxin: electrophysiological and in situ hybridization studies

The feeding responses evoked by cholecystokinin are mediated by vagus and splanchnic nerves

Total or selective branch vagotomy attenuates the reduction of cumulative food intake by cholecystokinin (CCK)-8 and CCK-33 respectively. However, the role of the sympathetic innervation of the gut and the role of the vagus nerve in feeding responses, which include meal size (MS) and intermeal interval (IMI), evoked by CCK-8 and CCK-33 have not been evaluated. Here, we tested the effects of total subdiaphragmatic vagotomy (VGX) and celiaco-mesenteric ganglionectomy (CMGX) on the previous feeding responses by CCK-8 and CCK-33 (0, 1, 3, and 5 nmol/kg given intraperitoneally). We found (1) that both peptides reduced meal size and CCK-8 (5 nmol) and CCK-33 (1 and 3 nmol) prolonged IMI, (2) that VGX attenuated the reduction of MS but failed to attenuate the prolongation of IMI by both peptides and (3) that CMGX attenuated the reduction of meal size by CCK-8 and the prolongation of IMI by both peptides. Therefore, the feeding responses evoked by CCK-8 require intact vagus and splanchnic nerves: the reduction of MS by CCK-33 requires an intact vagus nerve, and the prolongation of IMI requires the splanchnic nerve. These findings demonstrate the differential peripheral neuronal mediation of the feeding responses evoked by CCK-8 and CCK-33.

Roles of gastro-oesophageal afferents in the mechanisms and symptoms of reflux disease

Oesophageal pain is one of the most common reasons for physician consultation and/or seeking medication. It is most often caused by acid reflux from the stomach, but can also result from contractions of the oesophageal muscle. Different forms of pain are evoked by oesophageal acid, including heartburn and non-cardiac chest pain, but the basic mechanisms and pathways by which these are generated remain to be elucidated. Both vagal and spinal afferent pathways are implicated by basic research. The sensitivity of afferent fibres within these pathways may become altered after acid-induced inflammation and damage, but the severity of symptoms in humans does not necessarily correlate with the degree of inflammation. Gastro-oesophageal reflux disease (GORD) is caused by transient relaxations of the lower oesophageal sphincter, which are triggered by activation of gastric vagal mechanoreceptors. Vagal afferents are therefore an emerging therapeutic target for GORD. Pain in the absence of excess acid reflux remains a major challenge for treatment.

Capsaicin (TRPV1 Agonist) therapy for pain relief: farewell or revival?

OBJECTIVE

In this review, we explain our current understanding of the molecular basis for pain relief by capsaicin and other transient receptor potential vanilloid subfamily, member 1 (TRPV1) agonists. We summarize disease-related changes in TRPV1 expression and its implications for therapy and potential adverse effects. Last, we provide an overview of the current clinical uses of topical and injectable TRPV1 agonist preparations in both oncologic and nononcologic populations.

METHOD

Search of MEDLINE and other databases.

RESULTS

The capsaicin receptor TRPV1 is a polymodal nociceptor exhibiting a dynamic threshold of activation that could be lowered under inflammatory conditions. Consistent with this model, TRPV1 knock-out mice are devoid of post-inflammatory thermal hyperalgesia. TRPV1 desensitization of primary sensory neurons is a powerful approach to relieve symptoms of nociceptive behavior in animal models of chronic pain. However, over-the-counter capsaicin creams have shown moderate to poor analgesic efficacy. This is in part related to low dose, poor skin absorption, and compliance factors. Recently developed site-specific capsaicin therapy with high-dose patches and injectable preparations seem to be safe and reportedly provide long-lasting analgesia with rapid onset.

CONCLUSIONS

We argue that TRPV1 agonists and antagonists are not mutually exclusive but rather complimentary pharmacologic approaches for pain relief and we predict a "revival" for capsaicin and other TRPV1 agonists in the clinical management of pain associated with inflammation, metabolic imbalances (eg, diabetes), infections (HIV), and cancer, despite the current focus of the pharmaceutical industry on TRPV1 antagonists.

Modulatory effect of CCK-8S on GABA-induced depolarization from rat dorsal root ganglion

CCK is a brain-gut peptide that is abundantly distributed in both gastrointestinal tract and mammalian brain. The sulfated octapeptide fragment of cholecystokinin (CCK-8S) has been shown to be involved in numerous physiological functions such as behavior, anxiety, learning/memory processes and neuropathic pain. CCK-8S is one of the strongest endogenous anti-opioid substances and suppresses opioid peptides-mediated 'pre-synaptic inhibition' of gamma-aminobutyric acid (GABA) release. Here we provide evidence that CCK-8S modulates GABA-evoked membrane depolarization in rat dorsal root ganglion (DRG) neurons using intracellular recording technique. Bath application CCK-8S-induced membrane depolarization in most of the rat DRG neurons. The depolarization was blocked by prolumide but not LY225910. Pretreatment with CCK-8S suppressed the GABA-evoked depolarization in a concentration-dependent manner. The CCK-8S inhibition was also time-dependent and reached the peak at about 2 min. The inhibitory effect of CCK-8S was strongly suppressed by pre-incubation of CCK-B receptor antagonist LY225910, phospholipase C inhibitor U73122, protein kinase C inhibitor chelerythrine and calcium chelator BAPTA-AM, respectively. The protein kinase A inhibitor H-89 did not affect CCK-8S effect. The results suggest that CCK-8S inhibits GABA-A receptor function by activation of CCK-B receptor followed by activation of intracellular PLC-Ca(2+)-PKC cascade. Thus, CCK-8S might enhance nociceptive information transmission through inhibition of the "pre-synaptic inhibition" evoked by GABA, which may explain its role in modulation of primary sensory information (especially pain).

Involvement of cholecystokinin in peripheral nociceptive sensitization during diabetes in rats as revealed by the formalin response

The possible pronociceptive role of peripheral cholecystokinin (CCK-8) as well as CCK(A) and CCK(B) receptors in diabetic rats was assessed. Subcutaneous injection of 0.5% formalin induced a greater nociceptive behavior in diabetic than in non-diabetic rats. Moreover, local peripheral injection of CCK-8 (0.1-100 microg) significantly increased 0.5% formalin-induced nociceptive activity in diabetic, but not in non-diabetic, rats. This effect was restricted to the formalin-injected paw as administration of CCK-8 into the contralateral paw was ineffective. Local peripheral administration of CCK-8, in the absence of formalin injection, produced a low level of, but significant increase in, flinching behavior in diabetic compared to non-diabetic rats. In addition, local peripheral administration of the non-selective CCK receptor antagonist proglumide (1-100 microg), CCK(A) receptor antagonist lorglumide (0.1-100 microg) or CCK(B) receptor antagonist CR-2945 (0.1-100 microg), but not vehicle or contralateral administration of CCK receptor antagonists, significantly reduced 0.5% formalin-induced flinching in diabetic rats. CR-2945 was the most effective drug in this condition. These effects were not observed in non-diabetic rats. The local peripheral pronociceptive effect of CCK-8 (100 microg) was significantly reduced by proglumide (100 microg), lorglumide (100 microg), and CR-2945 (100 microg). Results suggest that diabetes-induced peripheral sensitization could be due to a local peripheral release of CCK-8, which in turn would act on CCK(B), mainly but also in CCK(A), receptors located on the primary afferent neurons.

The endogenous opioid system and clinical pain management

The endogenous opioid system is one of the most studied innate pain-relieving systems. This system consists of widely scattered neurons that produce three opioids: beta-endorphin, the met- and leu-enkephalins, and the dynorphins. These opioids act as neurotransmitters and neuromodulators at three major classes of receptors, termed mu, delta, and kappa, and produce analgesia. Like their endogenous counterparts, the opioid drugs, or opiates, act at these same receptors to produce both analgesia and undesirable side effects. This article examines some of the recent findings about the opioid system, including interactions with other neurotransmitters, the location and existence of receptor subtypes, and how this information drives the search for better analgesics. We also consider how an understanding of the opioid system affects clinical responses to opiate administration and what the future may hold for improved pain relief. The goal of this article is to assist clinicians to develop pharmacological interventions that better meet their patient's analgesic needs.

Expression and regulation of cholecystokinin and cholecystokinin receptors in rat nodose and dorsal root ganglia

Cholecystokinin (CCK) is an important satiety factor, acting via the vagus nerve to influence central feeding centers. CCK binding sites have been demonstrated in the vagal sensory nodose ganglion and within the nerve proper. Using in situ hybridization, expression of the CCK(A) and (B) receptors (Rs), as well as of CCK itself, was studied in the normal nodose ganglion (NG), and after vagotomy, starvation and high-fat diet. CCK(A)-R mRNA expression in dorsal root ganglia (DRGs) was also explored. In the NG, 33% of the neuron profiles (NPs) contained CCK(A)-R mRNA and in 9% we observed CCK(B)-R mRNA. CCK mRNA was not found in normal NGs. Peripheral vagotomy decreased the number of CCK(A)-R mRNA-expressing NPs, dramatically increased the number of CCK(B)-R mRNA, and induced CCK mRNA and preproCCK-like immunoreactivity in nodose NPs. No significant differences in the number of NPs labelled for either mRNA species were detected following 48 h food deprivation or in rats fed a high-fat content diet. In DRGs, 10% of the NPs expressed CCK(A)-R mRNA, a number that was not affected by either axotomy or inflammation. This cell population was distinct from neurons expressing calcitonin gene-related peptide mRNA. These results demonstrate that the CCK(A)-R is expressed by both viscero- and somatosensory primary sensory neurons, supporting a role for this receptor as a mediator both of CCK-induced satiety and in sensory processing at the spinal level. The stimulation of CCK and CCK(B)-R gene expression following vagotomy suggests a possible involvement in the response to injury for these molecules.