Profiling neurotransmitter receptor expression in the Ambystoma mexicanum brain

The serotonin reuptake blocker citalopram destabilizes fictive locomotor activity in salamander axial circuits through 5-HT1A receptors

Serotoninergic (5-HT) neurons are powerful modulators of spinal locomotor circuits. Most studies on 5-HT modulation focused on the effect of exogenous 5-HT and these studies provided key information about the cellular mechanisms involved. Less is known about the effects of increased release of endogenous 5-HT with selective serotonin reuptake inhibitors. In mammals, such molecules were shown to destabilize the fictive locomotor output of spinal limb networks through 5-HT_1A receptors. However, in tetrapods little is known about the effects of increased 5-HT release on the locomotor output of axial networks, which are coordinated with limb circuits during locomotion from basal vertebrates to mammals. Here, we examined the effect of citalopram on fictive locomotion generated in axial segments of isolated spinal cords in salamanders, a tetrapod where raphe 5-HT reticulospinal neurons and intraspinal 5-HT neurons are present as in other vertebrates. Using electrophysiological recordings of ventral roots, we show that fictive locomotion generated by bath-applied glutamatergic agonists is destabilized by citalopram. Citalopram-induced destabilization was prevented by a 5-HT_1A receptor antagonist, whereas a 5-HT_1A receptor agonist destabilized fictive locomotion. Using immunofluorescence experiments, we found 5-HT-positive fibers and varicosities in proximity with motoneurons and glutamatergic interneurons that are likely involved in rhythmogenesis. Our results show that increasing 5-HT release has a deleterious effect on axial locomotor activity through 5-HT_1A receptors. This is consistent with studies in limb networks of turtle and mouse, suggesting that this part of the complex 5-HT modulation of spinal locomotor circuits is common to limb and axial networks in limbed vertebrates.NEW & NOTEWORTHY Little is known about the modulation exerted by endogenous serotonin on axial locomotor circuits in tetrapods. Using axial ventral root recordings in salamanders, we found that a serotonin reuptake blocker destabilized fictive locomotor activity through 5-HT_1A receptors. Our anatomical results suggest that serotonin is released on motoneurons and glutamatergic interneurons possibly involved in rhythmogenesis. Our study suggests that common serotoninergic mechanisms modulate axial motor circuits in amphibians and limb motor circuits in reptiles and mammals.

Cloning and characterization of the ionotropic GABA receptor subunit ρ1 from pig (Sus scrofa)

Since human and pig eyes have remarkably anatomical and physiological similitudes swine models have been broadly used for functional studies and therapeutic research. Recently, a GABAρ-mediated relaxation of retinal vascularity suggested that GABAρ signaling may be used to improve retinal blood flow in vascular-driven impaired vision, and a further molecular characterization of GABAρ receptors would be beneficial. However, none of the GABAρ type subunits from pigs has been yet cloned; Among the 19 subunits that compose the family of GABAA receptors, ρ1-3 subunits are capable of forming homomeric channels. These homomeric receptors are particularly interesting because their pharmacological and kinetic properties are notably different from receptors composed by other GABAA subunits. Here we report the cloning of the GABAρ1subunit from the pig and the functional expression of homomeric channels in Xenopus oocytes. The most notable difference found in the pig GABAρ1 receptor was the absence of a stretch of 17 amino acids near the amino terminus (R41-V58) conserved in the rat and the human. This sequence has a higher nucleotidic match with the transcript variant 2 of the human GABAρ1 subunit. Xenopus oocytes injected with cRNA from the receptor generated currents when exposed to GABA that shared all the characteristics of other GABAρ1 subunits in mammals, including its modulation by dopamine. This study will help to increase the knowledge of the genetics of the pig, further the understanding of this important neurotransmitter receptor family and will shed some light in the evolution of these genes among mammals.