Prenatal GABAB1 and GABAB2 receptors: cellular and subcellular organelle localization in early fetal rat cortical neurons

The Untouchable Ventral Nucleus of the Trapezoid Body: Preservation of a Nucleus in an Animal Model of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by repetitive behaviors, poor social skills, and difficulties with communication and hearing. The hearing deficits in ASD range from deafness to extreme sensitivity to routine environmental sounds. Previous research from our lab has shown drastic hypoplasia in the superior olivary complex (SOC) in both human cases of ASD and in an animal model of autism. However, in our study of the human SOC, we failed to find any changes in the total number of neurons in the ventral nucleus of the trapezoid body (VNTB) or any changes in cell body size or shape. Similarly, in animals prenatally exposed to the antiepileptic valproic acid (VPA), we failed to find any changes in the total number, size or shape of VNTB neurons. Based on these findings, we hypothesized that the neurotransmitter profiles, ascending and descending axonal projections of the VNTB are also preserved in these neurodevelopmental conditions. We investigated this hypothesis using a combination of immunohistochemistry and retrograde tract tracing. We found no difference between control and VPA-exposed animals in the number of VNTB neurons immunoreactive for choline acetyltransferase (ChAT). Additionally, we investigated the ascending projections from the VNTB to both the central nucleus of the inferior colliculus (CNIC) and medial geniculate (MG) and descending projections to the cochlea. Our results indicate no significant differences in the ascending and descending projections from the VNTB between control and VPA-exposed animals despite drastic changes in these projections from surrounding nuclei. These findings provide evidence that certain neuronal populations and circuits may be protected against the effects of neurodevelopmental disorders.

Astrocytes, neurons, synapses: a tripartite view on cortical circuit development

In the mammalian cerebral cortex neurons are arranged in specific layers and form connections both within the cortex and with other brain regions, thus forming a complex mesh of specialized synaptic connections comprising distinct circuits. The correct establishment of these connections during development is crucial for the proper function of the brain. Astrocytes, a major type of glial cell, are important regulators of synapse formation and function during development. While neurogenesis precedes astrogenesis in the cortex, neuronal synapses only begin to form after astrocytes have been generated, concurrent with neuronal branching and process elaboration. Here we provide a combined overview of the developmental processes of synapse and circuit formation in the rodent cortex, emphasizing the timeline of both neuronal and astrocytic development and maturation. We further discuss the role of astrocytes at the synapse, focusing on astrocyte-synapse contact and the role of synapse-related proteins in promoting formation of distinct cortical circuits.

Effect of DYRK1A activity inhibition on development of neuronal progenitors isolated from Ts65Dn mice

Overexpression of dual-specificity tyrosine-(Y)-phosphorylation-regulated kinase 1A (DYRK1A), encoded by a gene located in the Down syndrome (DS) critical region, is considered a major contributor to developmental abnormalities in DS. DYRK1A regulates numerous genes involved in neuronal commitment, differentiation, maturation, and apoptosis. Because alterations of neurogenesis could lead to impaired brain development and mental retardation in individuals with DS, pharmacological normalization of DYRK1A activity has been postulated as DS therapy. We tested the effect of harmine, a specific DYRK1A inhibitor, on the development of neuronal progenitor cells (NPCs) isolated from the periventricular zone of newborn mice with segmental trisomy 16 (Ts65Dn mice), a mouse model for DS that overexpresses Dyrk1A by 1.5-fold. Trisomy did not affect the ability of NPCs to expand in culture. Twenty-four hours after stimulation of migration and neuronal differentiation, NPCs showed increased expression of Dyrk1A, particularly in the trisomic cultures. After 7 days, NPCs developed into a heterogeneous population of differentiating neurons and astrocytes that expressed Dyrk1A in the nuclei. In comparison with disomic cells, NPCs with trisomy showed premature neuronal differentiation and enhanced γ-aminobutyric acid (GABA)-ergic differentiation, but astrocyte development was unchanged. Harmine prevented premature neuronal maturation of trisomic NPCs but not acceleration of GABA-ergic development. In control NPCs, harmine treatment caused altered neuronal development of NPCs, similar to that in trisomic NPCs with Dyrk1A overexpression. This study suggests that pharmacological normalization of DYRK1A activity may have a potential role in DS therapy.

Neuroprotective effect of vitamin C against the ethanol and nicotine modulation of GABA(B) receptor and PKA-alpha expression in prenatal rat brain

Prenatal ethanol exposure has various deleterious effects on neuronal development and can induce various defects in developing brain, resulting in fetal alcohol syndrome (FAS). gamma-Aminobutyric acid (GABA(B)) receptor (R) is known to play an important role during the development of the central nervous system (CNS). Our study was designed to investigate the effect of ethanol (100 mM), nicotine (50 microM) (for 30 min and 1 h), vitamin C (vitC, 0.5 mM), ethanol plus vitC, and nicotine plus vitC on expression level of GABA(B1), GABA(B2)R, and protein kinase A-alpha (PKA) in prenatal rat cortical and hippocampal neurons at gestational days (GD) 17.5. The results showed that, upon ethanol and nicotine exposure, GABA(B1) and GABA(B2)R protein expression increased significantly in the cortex and hippocampus for a short (30 min) and long term (1 h), whereas only GABA(B2)R subunit was decreased upon nicotine exposure for a long term in the cortex. Furthermore, PKA expression in cortex and hippocampus increased with ethanol exposure during short term, whereas long-term exposure results increased in cortex and decreased in hippocampus. Moreover, the cotreatment of vitC with ethanol and nicotine showed significantly decreased expression of GABA(B1), GABA(B2)R, and PKA in cortex and hippocampus for a long-term exposure. Mitochondrial membrane potential, Fluoro-jade-B, and propidium iodide staining were used to elucidate possible neurodegeneration. Our results suggest the involvement of GABA(B)R and PKA in nicotine and ethanol-mediated neurodevelopmental defects and the potential use of vitC as a effective protective agent for FAS-related deficits.

Temporal migration of gonadotrophin-releasing hormone-1 neurones is modified in GAD67 knockout mice

Gonadotrophin-releasing hormone (GnRH-1) neurones reside in the forebrain and regulate gonadal function via the hypothalamic-pituitary-gonadal axis. Disruption of this axis results in reproductive dysfunction. During embryonic development, GnRH-1 neurones migrate from the nasal pit through the nasal/forebrain junction (NFJ) into the developing brain. Prenatally gamma-aminobutyric acid (GABA) is excitatory and has been shown to play a role in nervous system development. Both in vivo and in vitro experiments suggest that GABA inhibits migration of GnRH-1 neurones. The present study examines the migration of GnRH-1 neurones in GAD67 knockout (KO) mice to further elucidate the role of GABA on GnRH-1 neuronal development. Three stages were examined, embryonic day (E)12.5, E14.5 and E17.5. GnRH-1 cell number and location were analysed by immunocytochemistry and in situ hybridisation histochemistry. The total number of GnRH-1 immunopositive cells was similar between wild-type (WT) and KO mice. However, significant differences were found in the overall distribution of GnRH-1 immunopositive cells in GAD67 KO compared to WT mice at all stages. Subsequent analysis by area revealed differences occurred at the NFJ with an increase in GnRH-1 cells in GAD67 KO at E14.5 and a decrease in GnRH-1 cells in GAD67 KO at E17.5. Comparable counts for cells expressing GnRH-1 transcript and protein were obtained. These data indicate that attenuated levels of GABA accelerate GnRH-1 cell migration in nasal areas as well as movement of GnRH-1 cells into the central nervous system at the NFJ.