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Bhattarai, Janardhan P,Roa, Juan,Herbison, Allan E,Han, Seong Kyu The Endocrine Society 2014 Endocrinology Vol.155 No.2
<P>The effect of serotonin (5-HT) on the electrical excitability of GnRH neurons was examined using gramicidin perforated-patch electrophysiology in transgenic GnRH-green fluorescent protein mice. In diestrous female, the predominant effect of 5-HT was inhibition (70%) with 50% of these cells also exhibiting a late-onset excitation. Responses were dose dependent (EC(50) = 1.2μM) and persisted in the presence of amino acid receptor antagonists and tetrodotoxin, indicating a predominant postsynaptic action of 5-HT. Studies in neonatal, juvenile, peripubertal, and adult mice revealed that 5-HT exerted less potent responses from GnRH neurons with advancing postnatal age in both sexes. In adult male mice, 5-HT exerted less potent hyperpolarizing responses with more excitations compared with females. In addition, adult proestrous female GnRH neurons exhibited reduced inhibition and a complete absence of biphasic hyperpolarization-excitation responses. Studies using 5-HT receptor antagonists demonstrated that the activation of 5-HT(1A) receptors mediated the inhibitory responses, whereas the excitation was mediated by the activation of 5-HT(2A) receptors. The 5-HT-mediated hyperpolarization involved both potassium channels and adenylate cyclase activation, whereas the 5-HT excitation was dependent on protein kinase C. The effects of exogenous 5-HT were replicated using fluoxetine, which enhances endogenous 5-HT levels. These studies demonstrate that 5-HT exerts a biphasic action on most GnRH neurons whereby a fast 5HT(1A)-mediated inhibition occurs alongside a slow 5-HT(2A) excitation. The balance of 5-HT-evoked inhibition vs excitation is developmentally regulated, sexually differentiated, and variable across the estrous cycle and may play a role in regulation of hypothalamic-pituitary-gonadal axis throughout postnatal development.</P>
Effects of human growth hormone on gonadotropin-releasing hormone neurons in mice
Bhattarai, Janardhan P.,Kim, Shin-Hye,Han, Seong-Kyu,Park, Mi-Jung The Korean Pediatric Society 2010 Clinical and Experimental Pediatrics (CEP) Vol.53 No.9
Purpose: Recombinant human growth hormone (rhGH) has been widely used to treat short stature. However, there are some concerns that growth hormone treatment may induce skeletal maturation and early onset of puberty. In this study, we investigated whether rhGH can directly affect the neuronal activities of of gonadotropin-releasing hormone (GnRH). Methods: We performed brain slice gramicidin-perforated current clamp recording to examine the direct membrane effects of rhGH on GnRH neurons, and a whole-cell voltage-clamp recording to examine the effects of rhGH on spontaneous postsynaptic events and holding currents in immature (postnatal days 13-21) and adult (postnatal days 42-73) mice. Results: In immature mice, all 5 GnRH neurons recorded in gramicidin-perforated current clamp mode showed no membrane potential changes on application of rhGH (0.4, $1{\mu}g/mL$). In adult GnRH neurons, 7 (78%) of 9 neurons tested showed no response to rhGH ($0.2-1{\mu}g/mL$) and 2 neurons showed slight depolarization. In 9 (90%) of 10 immature neurons tested, rhGH did not induce any membrane holding current changes or spontaneous postsynaptic currents (sPSCs). There was no change in sPSCs and holding current in 4 of 5 adult GnRH neurons. Conclusion: These findings demonstrate that rhGH does not directly affect the GnRH neuronal activities in our experimental model.
Potentiation of NMDA receptors by Withania somnifera on hippocampal CA1 pyramidal neurons.
Bhattarai, Janardhan Prasad,Park, Soo Joung,Han, Seong Kyu Institute for Advanced Research in Asian Science a 2013 The American journal of Chinese medicine Vol.41 No.3
<P>In Ayurveda,Withania somnifera (WS) is used as a medicine to maintain mental and physical health as well as to enhance memory. In this study, the methanolic extract of WS(mWS) was tested for its electrical influence on hippocampal CA1 pyramidal neurons using a patch clamp technique. In current clamp mode under a high chloride pipette solution, mWS (400 ng/μl) induced remarkable membrane depolarization (9.75 2.54 mV, n = 6) of CA1 neurons. The mWS-induced depolarization was dose-dependent, reproducible, and persistent in the presence of 0.5 μM tetrodotoxin (TTX, 10.17 0.04 mV, n = 6). In voltage clamp mode (holding potential = -60 mV), mWS induced a dose-dependent non-desensitizing inward current that persisted in the presence of TTX (0.5 μM), suggesting that the response induced by mWS was purely a postsynaptic event. Interestingly, these inward currents were partially blocked by strychnine, a glycine receptor blocker. Further, mWS potentiated the NMDA response in hippocampal CA1 neurons at low concentrations. Overall, these results suggest that there are compounds in WS with possible glycine mimetic activities, which may be potential targets for inducing memory consolidation in hippocampal CA1 neurons.</P>
Medknow Publications 2016 The Chinese journal of physiology Vol.59 No.1
<P>Shilajit, a mineral pitch, has been used in Ayurveda and Siddha system of medicine to treat many human ailments, and is reported to contain at least 85 minerals in ionic form. This study examined the possible mechanism of Shilajit action on preoptic hypothalamic neurons using juvenile mice. The hypothalamic neurons are the key regulator of many hormonal systems. In voltage clamp mode at a holding potential of -60 mV, and under a high chloride pipette solution, Shilajit induced dose-dependent inward current. Shilajit-induced inward currents were reproducible and persisted in the presence of 0.5 mu M tetrodotoxin (TTX) suggesting a postsynaptic action of Shilajit on hypothalamic neurons. The currents induced by Shilajit were almost completely blocked by 2 mu M strychnine (Stry), a glycine receptor antagonist. In addition, Shilajit-induced inward currents were partially blocked by bicuculline. Under a gramicidin-perforated patch clamp mode, Shilajit induced membrane depolarization on juvenile neurons. These results show that Shilajit affects hypothalamic neuronal activities by activating the Stry-sensitive glycine receptor with alpha(2)/alpha(2)beta subunit. Taken together, these results suggest that Shilajit contains some ingredients with possible glycine mimetic activities and might influence hypothalamic neurophysiology through activation of Stry-sensitive glycine receptor-mediated responses on hypothalamic neurons postsynaptically.</P>
Nitric oxide suppresses L-type calcium currents in basilar artery smooth muscle cells in rabbits
Sharma, Naveen,Bhattarai, Janardhan Prasad,Hwang, Pyoung Han,Han, Seong Kyu Informa UK (TaylorFrancis) 2013 Neurological research Vol.35 No.4
<P>Nitric oxide (NO) is well known to be a vasodilator, and NO donor compounds are currently used for treating vasospasm following subarachnoid hemorrhage. However, the action mechanism of cerebral vascular relaxation is not yet clear. L-type calcium channels have been determined to play an essential role in smooth muscle contraction. To investigate the role of L-type calcium channels in NO-induced relaxation of basilar smooth muscle cells, we examined the effect of the NO donor, sodium nitroprusside (SNP) on calcium (Ca2+) currents using smooth muscle cells isolated from a rabbit basilar artery.</P>
Yiming Shen,Janardhan P. Bhattarai,Soo Joung Park,Gyu Seung Lee,Pan Dong Ryu,Seong Kyu Han 대한수의학회 2018 Journal of Veterinary Science Vol.19 No.2
It has been reported that Korean red ginseng (KRG), a valuable and important traditional medicine, has varied effects on the central nervoussystem, suggesting its activities are complicated. The paraventricular nucleus (PVN) neurons of the hypothalamus has a critical role in stressresponses and hormone secretions. Although the action mechanisms of KRG on various cells and systems have been reported, the directmembrane effects of KRG on PVN neurons have not been fully described. In this study, the direct membrane effects of KRG on PVN neuronalactivity were investigated by using a perforated patch-clamp in ICR mice. In gramicidin perforated patch-clamp mode, KRG extract (KRGE)induced repeatable depolarization followed by hyperpolarization of PVN neurons. The KRGE-induced responses were concentrationdependentand persisted in the presence of tetrodotoxin, a voltage sensitive Na+ channel blocker. The KRGE-induced responses weresuppressed by 6-cyano-7-nitroquinoxaline-2,3-dione (10 μM), a non–N-methyl-D-aspartate (NMDA) glutamate receptor antagonist, but notby picrotoxin, a type A gamma-aminobutyric acid receptor antagonist. The results indicate that KRG activates non-NMDA glutamate receptorsof PVN neurons in mice, suggesting that KRG may be a candidate for use in regulation of stress responses by controlling autonomic nervoussystem and hormone secretion.
Dong Hyu Cho,Janardhan Prasad Bhattarai,Seong Kyu Han 고려인삼학회 2012 Journal of Ginseng Research Vol.36 No.1
Korean red ginseng (KRG) has been used worldwide as a traditional medicine for the treatment of various reproductive diseases. Gonadotropin releasing hormone (GnRH) neurons are the fundamental regulators of pulsatile release of gonadotropin required for fertility. In this study, an extract of KRG (KRGE) was applied to GnRH neurons to identify the receptors activated by KRGE. The brain slice patch clamp technique in whole cell and perforated patch was used to clarify the effect of KRGE on the membrane currents and membrane potentials of GnRH neurons. Application of KRGE (3 ㎍/μL) under whole cell patch induced remarkable inward currents (56.17±7.45 pA, n=25) and depolarization (12.91±3.80 ㎷, n=4) in GnRH neurons under high Cl? pipette solution condition. These inward currents were not only reproducible, but also concentration dependent. In addition, inward currents and depolarization induced by KRGE persisted in the presence of the voltage gated Na? channel blocker tetrodotoxin (TTX), suggesting that the responses by KRGE were postsynaptic events. Application of KRGE under the gramicidin perforated patch induced depolarization in the presence of TTX suggesting its physiological signifi cance on GnRH response. Further, the KRGEinduced inward currents were partially blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; non-NMDA glutamate receptor antagonist, 10 μM) or picrotoxin (PIC; GABAA receptor antagonist, 50 μM), and almost blocked by PIC and CNQX mixture. Taken together, these results suggest that KRGE contains ingredients with possible GABA and non-NMDA glutamate receptor mimetic activity, and may play an important role in the endocrine function of reproductive physiology, via activation of GABAA and non-NMDA glutamate receptors in GnRH neurons.