Maternal effects in infant and adult phenotypes of 5HT1A and 5HT1B receptor knockout mice

The influence of the pre- and postweaning maternal environment on the offspring's phenotype was examined in 5-HT1A and 5-HT1B receptor knockout mice (KO1A and KO1B, respectively). We have previously shown that, when born to and raised by homozygous dams of the same genotype, adult KO1A are more anxious than wild-type (WT) mice, and adult KO1B are hyperactive and slightly less anxious than WT mice. We extend our studies here to the behavioral results of the offspring's own genotype, when the dam's genotype is constant, and the effects of the dam's genotype when the offspring's genotype is constant. In Experiments 1 and 2, KO1A-/- pups produced less ultrasonic vocalizations (USV) than controls in an isolation test on postnatal Day 7 when born to and reared by KO1A dams, either -/- or +/-. Heterozygous F1 pups reared by KO1A-/- dams produced more USV and were less anxious in the plus-maze at 2 to 3 months of age than F1 pups born to and reared by WT dams (Experiment 3). F1 pups reared by KO1B-/- dams produced less USV and were more anxious in the plus-maze than F1 pups reared by WT dams (Experiment 4). The results support a role for maternal effects that may comprise direct effects such as the dam's behavior and nutritional care of the pup, and possibly more complex indirect effects through the establishment of idiosyncratic dam-pup dyadic interactions. We recommend that breeding techniques that rely on same genotype (mutant-mutant or WT-WT) breeding pairs not be used to generate offspring when the focus of research is the study of gene function, but rather when familial effects need to be studied.     

Role of 5‐HT2A, 5‐HT4 and 5‐HT7 receptors in the antigen‐induced airway hyperresponsiveness in guinea‐pigs

Background A possible role of 5‐hydroxytryptamine (5‐HT) in the origin of antigen‐induced airway hyperresponsiveness (AI‐AHR) has been scarcely investigated. Objective To explore the participation of different 5‐HT receptors in the development of AI‐AHR in guinea‐pigs. Methods Lung resistance was measured in anaesthetized guinea‐pigs sensitized to ovalbumin (OVA). Dose–response curves to intravenous (i.v.) acetylcholine (ACh) were performed before and 1 h after antigenic challenge and expressed as the 200% provocative dose (PD₂₀₀). Organ bath experiments, confocal microscopy and RT‐PCR were additionally used. The 5‐HT content in lung homogenates was measured by HPLC. Results Antigenic challenge significantly decreased PD₂₀₀, indicating the development of AI‐AHR. This hyperresponsiveness was abolished by a combination of methiothepin (5‐HT₁/5‐HT₂/5‐HT₅/5‐HT₆/5‐HT₇ receptors antagonist) and tropisetron (5‐HT₃/5‐HT₄ antagonist). Other 5‐HT receptor antagonists showed three different patterns of response. Firstly, WAY100135 (5‐HT_1A antagonist) and ondansetron (5‐HT₃ antagonist) did not modify the AI‐AHR. Secondly, SB269970 (5‐HT₇ antagonist), GR113808 (5‐HT₄ antagonist), tropisetron or methiothepin abolished the AI‐AHR. Thirdly, ketanserin (5‐HT_2A antagonist) produced airway hyporresponsiveness. Animals with bilateral vagotomy did not develop AI‐AHR. Experiments in tracheal rings showed that pre‐incubation with LP44 or cisapride (agonists of 5‐HT₇ and 5‐HT₄ receptors, respectively) induced a significant increase of the cholinergic contractile response to the electrical field stimulation. In sensitized lung parenchyma strips, ketanserin diminished the contractile responses to ACh. Sensitization was associated with a ninefold increase in the 5‐HT content of lung homogenates. Confocal microscopy showed that sensitization enhanced the immunolabelling and co‐localization of nicotinic receptor and 5‐HT in airway epithelium, probably located in pulmonary neuroendocrine cells (PNECs). RT‐PCR demonstrated that neither sensitization nor antigen challenge modified the 5‐HT_2A receptor mRNA levels. Conclusions Our results suggested that 5‐HT was involved in the development of AI‐AHR to ACh in guinea‐pigs. Specifically, 5‐HT_2A, 5‐HT₄ and 5‐HT₇ receptors seem to be particularly involved in this phenomenon. Participation of 5‐HT might probably be favoured by the enhancement of the PNECs 5‐HT content observed after sensitization. Cite this as: P. Segura, M. H. Vargas, G. Córdoba‐Rodríguez, J. Chávez, J. L. Arreola, P. Campos‐Bedolla, V. Ruiz, L. M. García‐Hernández, C. Méndez and L. M. Montaño, Clinical & Experimental Allergy, 2010 (40) 327– 338.     

Heme oxygenase protects hippocampal neurons from ethanol-induced neurotoxicity

Ethanol has deleterious effects on neuronal cells both in vivo and in vitro, but the mechanisms are unknown. Here, treatment with increasing doses of ethanol (from 20 up to 600mM) decreased the viability of a mouse hippocampal neuroblastoma cell line, HT22. The glutathione concentration decreased and intracellular reactive oxygen species (ROS) increased in a dose-and time-dependent manner, suggesting that the neurotoxicity was due to oxidative stress. Expression of heme oxygenase (HO)-1, a redox regulator and heat shock protein, increased with time after ethanol treatment, but HO-2 was expressed constitutively. The addition of 5microM zinc protoporphyrin IX (ZnPP IX), a competitive HO inhibitor, with the ethanol further reduced cell viability and increased intracellular ROS, but these effects were reversed by co-treatment with 50nM bilirubin, a well-known antioxidant and a product of HO catalysis. These results suggest that HO has a protective role in hippocampal neurons as an intrinsic factor against ethanol-induced oxidative stress and the protection depends on the degree of oxidative stress.     

Luminal 5‐HT4 receptors—A successful target for prokinetic actions

The prokinetic effects of 5‐HT₄ receptor (5‐HT₄R) agonists have been utilized clinically for almost three decades to relieve symptoms of constipation. Surprisingly, the mechanism(s) of action of these compounds is still being debated. Recent studies highlight luminal 5‐HT₄Rs as an alternative and effective target for these prokinetic agents. These include the study by Shokrollahi et al (2019, Neurogastroenterol Motil, e13598) published in the current issue of Neurogastroenterology and Motility, who found that activation of mucosal 5‐HT₄Rs by intraluminal prucalopride, significantly enhanced propulsive motor patterns in rabbit colon. The authors highlight the idea that development of agonists targeting luminal 5‐HT₄Rs in the colonic mucosa might be more effective and safer in achieving prokinetic effects on intestinal motility. The purpose of this mini‐review is to discuss the evidence for luminal 5‐HT₄Rs as an emerging target for prokinetic agents in facilitating propulsive motor patterns in the colon.     

Serotonin‐2C receptor agonists decrease potassium‐stimulated GABA release in the nucleus accumbens

The serotonin 5‐HT_2C receptor has shown promise in vivo as a pharmacotherapeutic target for alcoholism. For example, recently, a novel 4‐phenyl‐2‐N,N‐dimethylaminotetralin (PAT) drug candidate, that demonstrates 5‐HT_2C receptor agonist activity together with 5‐HT_2A/2B receptor inverse agonist activity, was shown to reduce operant responding for ethanol after peripheral administration to rats. Previous studies have shown that the 5‐HT_2C receptor is found throughout the mesoaccumbens pathway and that 5‐HT_2C receptor agonism causes activation of ventral tegmental area (VTA) GABA neurons. It is unknown what effect 5‐HT_2C receptor modulation has on GABA release in the nucleus accumbens core (NAcc). To this end, microdialysis coupled to capillary electrophoresis with laser‐induced fluorescence was used to quantify extracellular neurotransmitter concentrations in the NAcc under basal and after potassium stimulation conditions, in response to PAT analogs and other 5‐HT_2C receptor modulators administered by reverse dialysis to rats. 5‐HT_2C receptor agonists specifically attenuated stimulated GABA release in the NAcc while 5‐HT_2C antagonists or inverse agonists had no effect. Agents with activity at 5‐HT_2A receptors had no effect on GABA release. Thus, in contrast to results reported for the VTA, current results suggest 5‐HT_2C receptor agonists decrease stimulated GABA release in the NAcc, and provide a possible mechanism of action for 5HT_2C‐mediated negative modulation of ethanol self‐administration. Synapse 69:78–85, 2015. © 2014 Wiley Periodicals, Inc.     

A selective,high affinity 5‐HT2B receptor antagonist inhibits visceral hypersensitivity in rats

Background RS‐127445 is a selective, high affinity 5‐HT_2Breceptor antagonist. We investigated whether 5‐HT_2Breceptor antagonists can reduce colonic visceral hypersensitivity caused by restraint stress or by proximal colonic inflammation. Methods Visceral hypersensitivity was induced in rats by either restraint stress or injection of 2, 4, 6‐trinitrobenzene sulfonic acid (TNBS) into the proximal colon. Restraint stress produced a significant increase in numbers of abdominal contractions evoked by colorectal distension (CRD), measured as a quantitative index of visceral nociception in rats. Seven days after TNBS injection, the pain threshold to CRD at the non‐inflamed distal colon, that was determined as the minimum pressure required to evoke abdominal cramp, was significantly decreased. The effect of RS‐127445 on visceral hypersensitivity was assessed in either naïve or TNBS‐treated rats. Key Results Oral administration of a selective, high affinity 5‐HT_2Breceptor antagonist, RS‐127445, significantly inhibited visceral hypersensitivity provoked by restraint stress (35 to 74% inhibition at 1 to 10 mg kg^?1). Oral RS‐127445 produced a significant suppression of TNBS‐induced visceral hypersensitivity (15 to 62% inhibition at 3 to 30 mg kg^?1), although it was without significant effect on the visceral nociceptive threshold of naïve rats. RS‐127445 (1 to 30 mg kg^?1, p.o.) also dose‐dependently reduced the restraint stress‐induced defecation in naïve and TNBS‐treated rats. Conclusions & Inferences These results suggest that 5‐HT_2Breceptors are involved in signaling from the colon in rats in which there is visceral hypersensitivity and that a selective 5‐HT_2Breceptor antagonist could have therapeutic potential for the treatment of gut disorders characterized by visceral hypersensitivity.     

An approach for serotonin depletion in pigs: Effects on serotonin receptor binding

Depletion of central serotonin (5‐HT) levels and dysfunction in serotonergic transmission are implicated in a variety of human CNS disorders. The mechanisms behind these serotonergic deficits have been widely studied using rodent models, but only to a limited extent in larger animal models. The pig is increasingly used as an experimental animal model especially in neuroscience research. Here, we present an approach for serotonin depletion in the pig brain. Central serotonin depletion in Danish Landrace pigs was achieved following 4 days treatment with para‐chlorophenylalanine (pCPA). On day 5, tissue concentrations of 5‐HT in seven distinct brain structures from one hemisphere: frontal and occipital cortex, striatum, hippocampus, cerebellum, rostral, and caudal brain stem, were determined. The other hemisphere was processed for receptor autoradiography. Treatments with 50 mg/kg and 100 mg/kg pCPA caused average decreases in 5‐HT concentrations of 61% ± 14% and 66% ± 16%, respectively, and a substantial loss of 5‐HT immunostaining was seen throughout the brain. The serotonin depletion significantly increased 5‐HT₄ receptor binding in nucleus accumbens, but did not alter 5‐HT_1A and 5‐HT_2A receptor or serotonin transporter binding in any brain region. In conclusion, 4 days treatment with pCPA effectively reduces 5‐HT levels in the pig brain. Further, whereas several 5‐HT markers did not change after the pCPA treatment, 5‐HT₄ receptors were consistently upregulated, indicating a greater susceptibility of this receptor to altered 5‐HT levels. This porcine model of serotonin depletion will be useful in future studies of cerebral serotonergic dysfunction. Synapse 2011. © 2010 Wiley‐Liss, Inc.     

Nigrostriatal upregulation of 5‐HT2A receptors correlates with motor dysfunction in progressive supranuclear palsy

A dysfunction of multiple neurotransmitter systems is assumed as a neurochemical basis of the akinetic‐rigid syndrome of progressive supranuclear palsy (PSP). In vitro studies have produced conflicting results on the serotoninergic system in PSP. We, therefore, studied the binding potential of the serotonin 2A (5‐HT_2A) receptor ligand [ 18 F]altanserin in 8 patients with clinically probable PSP and 13 healthy controls using positron emission tomography. We found an up‐regulation of 5‐HT_2A receptors in the substantia nigra and, to a lower degree, in the striatum, while neocortical 5‐ HT_2A receptor densities showed no changes upon partial‐volume correction. Nigral and striatal receptor changes were significantly correlated with patients' scores of motor dysfunction (UPDRS III, PSP‐rating scale) pointing to a functional relevance of the described findings. © 2009 Movement Disorder Society