Changes in Gene Expression at Inhibitory Synapses in Response to Taurine Treatment. In: El Idrissi A, L'amoreaux WJ, editors. Taurine 8. New York: Springer; 2013. pp. 187-94. [DOI: 10.1007/978-1-4614-6130-2_16]

Taurine-Derived Compounds Produce Anxiolytic Effects in Rats Following Developmental Lead Exposure

Lead (Pb2+) is a developmental neurotoxicant that disrupts the GABA-shift and subsequently causes alterations in the brain's excitation-to-inhibition (E/I) balance. Taurine is a well-established neuroprotective and inhibitory compound for regulating brain excitability. Since mechanistically taurine can facilitate neuronal inhibition through the GABA-AR, the present study examined the anxiolytic potential of taurine derivatives. Treatment groups consisted of the following developmental Pb2+-exposures: Control (0 ppm) and Perinatal (150 ppm or 1,000 ppm lead acetate in the drinking water). Rats were scheduled for behavioral tests between postnatal days (PND) 36-45 with random drug assignments to either saline, taurine, or taurine-derived compound (TD-101, TD-102, or TD-103) to assess the rats' responsivity to each drug in mitigating the developmental Pb2+-exposure and anxiety-like behaviors through the GABAergic system. Long-Evans hooded rats were assessed using an open field (OF) test for preliminary locomotor assessment. Twenty-four hours later, the same rats were exposed to the elevated plus maze (EPM) and were given an i.p. injection of 43 mg/Kg of the saline, taurine, or TD drugs 15 min prior to testing. Each rat was tested using the triple-blind random assignment method for each drug condition. The OF data revealed that Control female rats had increased locomotor activity over Control male rats, and the Pb2+-exposed males and females had increased locomotor activity when compared to the Control male and female rats. However, in the EPM, the Control female rats exhibited more anxiety-like behaviors over Control male rats, and the Pb2+-exposed male and female rats showed selective responsivity to TD drugs when compared to taurine. For Pb2+-exposed males, TD-101 showed consistent recovery of anxiety-like behaviors similar to that of taurine regardless of Pb2+ dose, whereas in Pb2+-exposed females TD-101 and TD-103 showed greater anxiolytic responses in the EPM. The results from the present psychopharmacological study suggests that taurine and its derivatives are interesting drug candidates to explore sex-specific mechanisms and actions of taurine and the associated GABAergic receptor properties by which these compounds alleviate anxiety as a potential behavioral pharmacotherapy for neurodevelopmental Pb2+ exposure.

Synaptic remodeling and reduced expression of the transcription factors, HES1 and HES5, in the cortex neurons of cognitively impaired hyperhomocysteinemic mice

Hyperhomocysteinemia (HHcy) is associated with cognitive impairment and neurodegenerative diseases. The synaptic ultrastructure and the expression of hairy enhancer of split (HES) genes are involved in cognitive impairment induced by HHcy, but their precise role remains unclear. The present study aimed to measure synaptic remodeling and the expression of HES1 and HES5 in the cortex neurons of mice with HHcy to clarify their role in cognitive impairment. Mild HHcy was induced in ApoE^-/- mice receiving a high-methionine diet. The correct response percentage, latency, and distance traveled in the mice with HHcy decreased compared with those of non-HHcy control mice (P < 0.05). There was no difference in the neuronal counts and the mean optical density of Nissl bodies in the frontal cortex of HHcy and non-HHcy mice. Increased apoptosis rates and numbers of autophagosomes were observed in the HHcy mice by TUNEL staining and electron microscopy, respectively, compared to those in the control group (P < 0.05). There was a significant increase in the area of postsynaptic density and size variation of synaptic vesicles in the HHcy group compared to that in the control (P < 0.05). Decreased expression of HES1 and HES5 was observed by western blotting and immunostaining in the HHcy group compared to that in the control (P < 0.05). Collectively, these results suggest that increased autophagy, apoptosis, synaptic remodeling, and downregulation of hes1 and hes5 are involved in the cognitive impairment induced by hyperhomocysteinemia.

Sub-chronic taurine administration induces behavioral sensitization but does not influence ethanol-induced dopamine release in the nucleus accumbens

Preclinical studies have shown that the amino acid taurine is of importance for the dopamine elevating properties of ethanol. Taurine intake has escalated over the last decade due to increased consumption of taurine-containing energy drinks and dietary supplements. Whether long-term intake of large amounts of taurine induces adaptations affecting ethanol-induced dopamine elevation is not clear. Thus the aim of the present studies was to explore the impact of repeated administration of large amounts of taurine on ethanol-induced behavior and dopamine neurotransmission. Repeated daily systemic administration of taurine increased taurine-induced locomotor activity and rearing. Acute administration of taurine and ethanol in naïve animals produced an additive effect on extracellular taurine but no alteration of the ethanol-induced dopamine elevation, as measured by in vivo microdialysis. Sub-chronic administration of taurine did not modify the taurine- or dopamine-elevating properties of ethanol. Daily taurine treatment also failed to change the mRNA expression of the taurine transporter and GABA_A- and glycine-receptor subunits, as measured by qPCR in nucleus accumbens tissue. We conclude that systemic administration of taurine may have long lasting central effects, here displayed as behavioral sensitization. However, repeated daily exposure to taurine does not appear to influence the dopamine elevating properties of ethanol.

Perinatal Pb2+ exposure alters the expression of genes related to the neurodevelopmental GABA-shift in postnatal rats

BACKGROUND

Lead (Pb2+) is an environmental neurotoxicant that disrupts neurodevelopment, communication, and organization through competition with Ca2+ signaling. How perinatal Pb2+ exposure affects Ca2+-related gene regulation remains unclear. However, Ca2+ activates the L-Type voltage sensitive calcium channel β-3 subunit (Ca-β3), which autoregulates neuronal excitability and plays a role in the GABA-shift from excitatory-to-inhibitory neurotransmission.

METHOD

A total of eight females (n = 4 Control and n = 4 Perinatal) and four males (n = 2 Control and n = 2 Perinatal) rats were used as breeders to serve as Dams and Sires. The Dam's litters each ranged from N = 6-10 pups per litter (M = 8, SD = 2), irrespective of Pb2+ treatment, with a majority of males over females. Since there were more males in each of the litters than females, to best assess and equally control for Pb2+- and litter-effects across all developmental time-points under study, female pups were excluded due to an insufficient sample size availability from the litter's obtained. From the included pup litters, 24 experimentally naïve male Long Evans hooded rat pups (Control N = 12; Pb2+ N = 12) were used in the present study.  Brains were extracted from rat prefrontal cortex (PFC) and hippocampus (HP) at postnatal day (PND) 2, 7, 14 and 22, were homogenized in 1 mL of TRIzol reagent per 100 mg of tissue using a glass-Teflon homogenizer. Post-centrifugation, RNA was extracted with chloroform and precipitated with isopropyl alcohol. RNA samples were then re-suspended in 100 μL of DEPC treated H2O. Next, 10 μg of total RNA was treated with RNase-free DNase (Qiagen) at 37 °C for 1 h and re-purified by a 3:1 phenol/chloroform extraction followed by an ethanol precipitation. From the purified RNA, 1 μg was used in the SYBR GreenER Two-Step qRT-PCR kit (Invitrogen) for first strand cDNA synthesis and the quantitative real-time PCR (qRT-PCR). The effects of perinatal Pb2+ exposure on genes related to early neuronal development and the GABA-shift were evaluated through the expression of: Ca-β3, GABAAR-β3, NKCC1, KCC2, and GAD 80, 86, 65, and 67 isoforms.

RESULTS

Perinatal Pb2+ exposure significantly altered the GABA-shift neurodevelopmental GOI expression as a function of Pb2+ exposure and age across postnatal development. Dramatic changes were observed with Ca-β3 expression consistent with a Pb2+ competition with L-type calcium channels. By PND 22, Ca-β3 mRNA was reduced by 1-fold and 1.5-fold in PFC and HP respectively, relative to controls. All HP GABA-β3 mRNA levels were particularly vulnerable to Pb2+ at PND 2 and 7, and both PFC and HP were negatively impacted by Pb2+ at PND 22. Additionally, Pb2+ altered both the PFC and HP immature GAD 80/86 mRNA expression particularly at PND 2, whereas mature GAD 65/67 were most significantly affected by Pb2+ at PND 22.

CONCLUSIONS

Perinatal Pb2+ exposure disrupts the expression of mRNAs related to the GABA-shift, potentially altering the establishment, organization, and excitability of neural circuits across development. These findings offer new insights into the altered effects Pb2+ has on the GABAergic system preceding what is known regarding Pb2+ insults unto the glutamatergic system.