VB20B7, a novel 5-HT-ergic agent with gastrokinetic activity. I. Interaction with 5-HT3 and 5-HT4 receptors

Identification of a novel 5-HT(4) receptor splice variant (r5-HT(4c1)) and preliminary characterisation of specific 5-HT(4a) and 5-HT(4b) receptor antibodies

The human 5-hydroxytryptamine (5-HT(4)) receptor is encoded by a highly complex gene which gives rise to at least 10 distinct splice variants. However, the functional relevance of these variants is unknown. In rat, only three such variants have been identified, 5-HT(4a) (r5-HT(4a)), 5-HT(4b) (r5-HT(4b)) and 5-HT(4e) (r5-HT(4e)). In the current study we identify and characterise the pharmacology of a novel rat splice variant (r5-HT(4c1)) and present the first comprehensive analysis of 5-HT(4) splice variant mRNA expression levels throughout the rat gastrointestinal tract. In addition, we describe preliminary characterisation of the first 5-HT(4) splice variant specific antibodies. In transfected cells, r5-HT(4c1) receptor exhibited similar binding properties to r5-HT(4a) and r5-HT(4b). Functional studies showed that 5-HT(4) agonists prucalopride (4-amino-5-chloro-2,3-dihydro-N-[1-(3-methoxypropyl)-4-piperidinyl]-7-benzofuran carboxamide monohydrochloride and renzapride (+/-)-endo-4-amino-5-chloro-2-methoxy-N-(1-azabicyclo[3.3.1]non-4-yl)benzamide monohydrochloride) acted as partial agonists at r5-HT(4c1), but full agonists at r5-HT(4a) and r5-HT(4b). Moreover, in contrast to r5-HT(4a) and r5-HT(4b), r5-HT(4c1) was not constitutively active. TaqMan mRNA analysis showed that r5-HT(4a) expression in brain and dorsal root ganglion exceeded that in the gastrointestinal tract, whilst the reverse was true for r5-HT(4b) and r5-HT(4c1). mRNA expression of each variant also increased distally throughout the gastrointestinal tract with the highest levels in the colon. r5-HT(4a) and r5-HT(4b) specific immunoreactivity was abundant on enteric neurons in jejunum, ileum and colon as well as neurons and satellite cells of the dorsal root ganglion. Only r5-HT(4b) immunoreactivity was observed on endocrine cells in the duodenum. These data could have implications in rat models and aid understanding of 5-HT(4) splice variant function.

Intracellular cAMP and calcium signaling by serotonin in mouse cumulus-oocyte complexes

cAMP and intracellular Ca2+ are important second messengers involved in mammalian follicular growth and oocyte meiotic maturation. We investigated the capacity of the neurohormone serotonin (5-hydroxytryptamine, 5-HT) to regulate intracellular cAMP and Ca2+ in mouse oocytes and surrounding cumulus cells. On the basis of a reverse transcription-polymerase chain reaction study, 5-HT7 receptor mRNA is expressed in cumulus cells, oocytes, and embryos up to the four-cell stage, and 5-HT2A and 5-HT2B receptor mRNAs are expressed in cumulus cells only, whereas 5-HT2C, 5-HT4, and 5-HT6 receptors are expressed in neither oocytes nor cumulus cells. The addition of 5-HT (10 nM to 10 microM) to isolated metaphase II oocytes had no effect on their internal cAMP or Ca2+ levels, whereas it caused dose-dependent cAMP and Ca2+ increases in cumulus cells. This cAMP increase in cumulus cells could be mimicked by 5-HT agonists with the following order of potency: 5-HT > 8-hydroxy-2-(di-n-propylamino) tetralin = alpha-methyl-5-HT = 5-carboxamidotryptamine maleate > 2-[1-(4-piperonyl)piperazinyl]benzo-triazole, thereby supporting a preferential involvement of 5-HT7 receptors. As measured with cumulus cells preloaded with fura-2/acetoxymethyl ester (AM), the addition of 5-HT also caused dose-dependent Ca2+ increases, which were probably linked to detected 5-HT2A and 5-HT2B receptors. Adding the Ca2+ ionophore ionomycin to cumulus cells resulted in both Ca2+ and cAMP elevations, whereas preincubation of cells with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM abolished the 5-HT-induced Ca2+ increase and reduced the cAMP increase, indicating cross-talk between the 5-HT-sensitive Ca2+ and cAMP pathways. Our results show that 5-HT may be a local regulator in mouse cumulus-oocyte complexes through its actions on cAMP and Ca2+ signaling, as mediated by 5-HT2A, 5-HT2B, and 5-HT7 receptors.

Evidence for altered basal ganglia and cortical functions in transient idiopathic dystonia

Idiopathic dystonia with onset in the first year of life has been described as a transient movement disorder, in contrast to other forms of idiopathic dystonia We report on a girl who showed, from her 5th month, episodes of dystonic postures of her neck and arm, which lasted for seconds and occurred several times a day. Neurologic findings and the psychomotor development were and remained normal. Neurometabolic screening tests and cerebral magnetic resonance imaging showed normal results. Functional cerebral imaging showed decreased perfusion of the basal ganglia and the left temperomesial cortex using single photon emission computed tomography (SPECT with technetium 99m hexamethylpropyleneamine oxime [99mTc-HMPAO]) and decreased glucose metabolism in the basal ganglia and the cerebellum using positron emission tomography (PET with [18F]fluorodeoxyglucose [18FDG]). Follow-up revealed that the episodes disappeared at the age of 16 months. The findings of PET and SPECT give evidence of an alteration in basal ganglia function but also in functions of other central nervous system regions, which may, however, be temporary.

Functional gut disorders: from motility to sensitivity disorders. A review of current and investigational drugs for their management

Functional gut disorders include several clinical entities defined on the basis of symptom patterns (e.g., functional dyspepsia, irritable bowel syndrome, functional abdominal pain, functional abdominal bloating), for which there is no established pathophysiological mechanism. Because there is no well-defined pathophysiological target, treatment should be aimed at symptom improvement. Prokinetics and antispasmodics have been widely used in the treatment of functional gut disorders on the assumption that disordered motility is the underlying cause of symptoms, and symptom improvement is indeed achievable with these compounds in some, but not all, patients with features of hypo- or hypermotility, respectively. In the first part of this review, we cover the basic pharmacology and discuss the rationale for the clinical use of prokinetics and antispasmodics. On the other hand, in the past few years, the explosive growth in the research focusing on visceral sensitivity and visceral reflexes has suggested that at least some patients with functional gut disorders have altered visceral perception. Thus, the second part of the review covers these developments and focuses on studies addressing the issue of drugs modulating visceral sensitivity.

VB20B7, a novel 5-HT-ergic agent with gastrokinetic activity. II. Evaluation of the gastroprokinetic activity in rats and dogs

The gastrokinetic activity of 2[1-(4-piperonyl)piperazinyl]benzothiazole (VB20B7), a new compound with 5-HT4 receptor agonist and weak 5-HT3 receptor antagonist properties has been studied in rats and dogs. The effects of VB20B7 were investigated in physiological conditions and in a model of gastroparesis induced by the alpha 2-adrenergic agonist UK-14304 and compared with cisapride. In rats, both VB20B7 and cisapride enhanced gastric emptying of indigestible solids (steel spheroids) and liquids (phenol red) at doses of 5-10 mg kg-1 by mouth. Gastric emptying of solid radiopaque markers in fasted beagle dogs was enhanced significantly by VB20B7 (0.25-1 mg kg-1 p.o.) whereas the effect of cisapride (0.5-2 mg kg-1 p.o.) did not reach statistical significance. Similar results were found when the radiopaque markers were given to the dogs following a standard solid meal. The delayed gastric emptying of indigestible solids and radiopaque markers by UK-14304 was reversed by oral administration of VB20B7 in both rats and dogs. Cisapride, however, was only effective in rats. In addition, gastric emptying of a digestible solid/liquid meal was assessed by quantitating the rate of appearance of the radioactive markers in the duodenum of dogs. VB20B7 (0.2-1 mg kg-1, i.v.) enhanced gastric emptying of both solid and liquid phases while cisapride only enhanced emptying of the solid phase. The present study indicates that acute oral and intravenous administration of VB20B7 accelerates gastric emptying of both solids and liquids in different animal models.