Early life GABAA blockade alters the synaptic plasticity and cognitive functions in male and female rats

Gamma-aminobutyric acid (GABA), the major inhibitory neurotransmitter in adults, has a critical contribution to balanced excitatory-inhibitory networks in the brain. Alteration in depolarizing action of GABA during early life is connected to a wide variety of neurodevelopmental disorders. Additionally, the effects of postnatal GABA blockade on neuronal synaptic plasticity are not known and therefore, we set out to determine whether postnatal exposure to bicuculline, a competitive antagonist of GABA_A receptors, affects electrophysiologic changes in hippocampal CA1 neurons later on. To this end, male and female Wistar rats received vehicle or bicuculline (300 μg/kg) on postnatal days (PNDs) 7, 9 and 11, and then underwent different behavioral and electrophysiological examinations in adulthood. Postnatal exposure to bicuculline did not affect basic synaptic transmission but led to a pronounced decrease in paired-pulse facilitation (PPF) in CA1 pyramidal neurons. Bicuculline treatment also attenuated the long-term potentiation (LTP) and long-term depression (LTD) of CA1 neurons accompanied by decreased theta-burst responses in male and female adult rats. These electrophysiology findings together with the reduced brain-derived neurotrophic factor (BDNF) levels in the hippocampus and prefrontal cortex reliably explain the disturbance in spatial reference and working memories of bicuculline-treated animals. This study suggests that postnatal GABA_A blockade deteriorates short- and long-term synaptic plasticity of hippocampal CA1 neurons and related encoding of spatial memory in adulthood.

Okadaic acid attenuates short-term and long-term synaptic plasticity of hippocampal dentate gyrus neurons in rats

Protein phosphorylation states have a pivotal role in regulation of synaptic plasticity and long-term modulation of synaptic transmission. Serine/threonine protein phosphatase 1 (PP1) and 2A (PP2A) have a critical effect on various regulatory mechanisms involved in synaptic plasticity, learning and memory. Okadaic acid (OKA), a potent inhibitor of PP1 and PP2A, reportedly leads to cognitive decline and Alzheimer's disease (AD)-like pathology. The aim of this study was to examine the effect of OKA on electrophysiological characteristics of hippocampal dentate gyrus (DG) neurons in vivo. Male Wistar rats were divided into two control and OKA groups. OKA was injected intracerebroventricularly (i.c.v.) into lateral ventricles and after two weeks the long-term potentiation (LTP) and paired-pulse responses recorded from hippocampal perforant path-DG synapses in order to assess short-term and long-term synaptic plasticity. Results of this study revealed that OKA-induced inhibition of PP1 and PP2A activity drastically attenuates the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude following paired pulse and high frequency stimulation (HFS) of hippocampal DG neurons indicating pre- and post-synaptic involvement in electrical activity of these neurons. Administration of OKA impaired the short-term and long-term spatial memories conducted by Y-maze and passive avoidance tests, respectively. OKA-induced attenuation in electrophysiological activity and consequent memory deficits also provide a beneficial tool for studying neurodegenerative disorders such as AD.

All trans retinoic acid modulates peripheral nerve fibroblasts viability and apoptosis

OBJECTIVE

Following peripheral nerve injury, residing fibroblasts start to proliferate and accumulate at the injury site and may participate in neuroma tissue evolution. Retinoic acid has been shown to regulate many cellular processes and to display anti-proliferative and anti-fibrotic properties. The aim of this study was to investigate the impact of all trans retinoic acid (ATRA) on rat peripheral nerve fibroblasts.

MATERIALS AND METHODS

Peripheral nerve fibroblasts and C166 cells were treated with increasing doses of ATRA (0.05 nM to 1 μM). The viability of cells was determined with 3-(4,5-dimethlthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. In addition, the number of peripheral nerve fibroblasts was counted after two days of ATRA treatment and alternatively up to the end of next week. Acridine orange/ethidium bromide double staining was implemented to morphologically visualize the possible mechanism of cell death. For apoptosis, caspase 3/7 activity was measured using Caspase-Glo 3/7 assay kit.

RESULTS

MTT assay revealed that 0.05-1 nM of ATRA reduces fibroblasts viabilities. Then, almost a plateau state was observed from 1 nM to 1 μM of ATRA exposure. Additionally, a deceleration in peripheral nerve fibroblasts growth was confirmed via cell counting. Quantification of acridine orange/ethidium bromide staining displayed highly increased number of early apoptotic cells following ATRA administration. Amplified activation of caspase 3/7 was in favor of apoptosis in ATRA treated peripheral nerve fibroblasts.

CONCLUSION

The data from the present study demonstrate that ATRA could interfere in peripheral nerve fibroblasts viabilities and induce apoptosis. Although more investigations are needed to be implemented, our in vitro results indicate that retinoic acid can probably help the regeneration of injured axon via reducing of fibroblasts growth.