GABAρ expression in the medial nucleus of the trapezoid body

GABAρ3 expression in lobule X of the cerebellum is reduced in the valproate model of autism

Autism spectrum disorder (ASD) is a group of developmental disorders characterized by social interaction deficits, communication impairments, and stereotyped and repetitive behaviors. Additionally, impairments in the GABAergic circuitry have been associated with ASD. Several studies have shown that dysfunction of the cerebellum is a hallmark of ASD, and postmortem studies in humans reported a reduced density of Purkinje cells (PCs) together with an abnormal expression of GABA_A subunits, among which GABAρ3 is expressed in early postnatal development, forms homomeric receptors with high affinity to the agonist (GABA EC₅₀ ∼ 3 μM) and desensitize very little upon activation. Thus, we tested if the expression of GABAρ3 was modified by prenatal exposure to valproate (VPA), a well-known murine model of autism. The latency to find the nest increased in VPA-treated mice when compared to controls at postnatal day 8 (P8). Immunofluorescence studies showed a reduced expression of GABAρ3 in Purkinje cells (PCs) and ependymal glial cells (EGCs) from lobule X of VPA-treated mice. Finally, the expression of GABAρ3 increases linearly throughout normal development of the cerebellum, but this pattern is disrupted in the VPA model of autism. We conclude that the expression of GABAρ3 is reduced in PCs and EGCs from lobule X of the cerebellum in the VPA model of autism. Thus, GABAρ3 may be a relevant marker for ASD etiology.

Neurotransmitters and Receptors Changes in Medial Nucleus of the Trapezoid Body (MNTB) of Early-Developmental Rats with Single-Side Deafness

BACKGROUND Congenital single-side deafness (SSD) affects sound localization even after cochlear implantation (CI) in some conditions. The medial nucleus of the trapezoid body (MNTB) plays an important role in binaural benefit and sound localization, but little is known about intrinsic molecular changes in MNTB with SSD. We aimed to observe changes in MNTB in early-developmental SSD rats, including the key neurotransmitters (GABA, Gly, Glu) and major receptors (GABAa-R/GABAb-R for GABA, Gly-R for Gly, and AMPA/NMDA for Glu). MATERIAL AND METHODS The model of early-developmental SSD was acquired by right cochlear ablation at P12 and confirmed by ABR. High-performance liquid chromatography fluorescence detection (HPLC-FLD) was performed to measure the levels of neurotransmitters in MNTB. The relative expression of neurotransmitter receptors was tested by quantitative real-time PCR analysis. RESULTS (1) The right MNTB of experimental rats had an increase in GABA, Gly, and Glu at 4 weeks after right cochlear ablation (P<0.05). (2) At 2 weeks, the left MNTB of experimental rats showed increases in GABAa-R, GABAb-R, Gly-R, and AMPA, while the right MNTB showed lower expression of NMDA (P<0.05). The higher receptors in left MNTB decreased to a level at which we found no difference at 1 week for GABAa-R and GABAb-R (P>0.05), and was even reversed for Gly-R and AMPA (P<0.05). (3) Gly level was significantly increased at 2 weeks bilaterally and continued to 4 weeks in the left MNTB (P<0.05). CONCLUSIONS Early-developmental SSD can lead to asymmetric distribution of neurotransmitters and receptors in MNTB, which can be the fundamental cause of defective sound localization after cochlear implantation.

GABAρ selective antagonist TPMPA partially inhibits GABA-mediated currents recorded from neurones and astrocytes in mouse striatum

The neostriatum plays a central role in motor coordination where nerve cells operate neuronal inhibition through GABAergic transmission. The neostriatum expresses a wide range of GABA-A subunits, including GABAρ1 and ρ2 which are restricted to a fraction of GABAergic interneurons and astrocytes. Spontaneous postsynaptic currents (sPSCs) evoked by 4-aminopyridine (4-AP) were recorded from neurones of the dorsal neostriatum, and their frequency was reduced > 50% by the selective GABAρ antagonist (1,2,5,6-Tetrahydropyridine-4-yl) methylphosphinic acid (TPMPA). Additionally, we recorded GABA evoked currents from astrocytes in vitro and in situ. Astrocytes in vitro showed modulation by pentobarbital and desensitization upon consecutive applications of GABA. However, modulation by pentobarbital was absent and no significant desensitization was detected from astrocytes in situ. Moreover, TPMPA-sensitive GABA-currents that were insensitive to bicuculline were also recorded from astrocytes in situ, consistent with our previous study where GABAρ expression was demonstrated. Finally, we assessed the mRNA expression of GABAρ3, through different stages of postnatal development; double immunofluorescence disclosed GABAρ3 expression in calretinin-positive interneurons as well as in astrocytes (>70%). These results add new information about the participation of GABAρ subunits in neostriatal interneurons and astrocytes.