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Lucas-Romero J, Rivera-Arconada I, Lopez-Garcia JA. Noise or signal? Spontaneous activity of dorsal horn neurons: patterns and function in health and disease. Pflugers Arch 2024:10.1007/s00424-024-02971-8. [PMID: 38822875 DOI: 10.1007/s00424-024-02971-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2023] [Revised: 04/10/2024] [Accepted: 05/05/2024] [Indexed: 06/03/2024]
Abstract
Spontaneous activity refers to the firing of action potentials by neurons in the absence of external stimulation. Initially considered an artifact or "noise" in the nervous system, it is now recognized as a potential feature of neural function. Spontaneous activity has been observed in various brain areas, in experimental preparations from different animal species, and in live animals and humans using non-invasive imaging techniques. In this review, we specifically focus on the spontaneous activity of dorsal horn neurons of the spinal cord. We use a historical perspective to set the basis for a novel classification of the different patterns of spontaneous activity exhibited by dorsal horn neurons. Then we examine the origins of this activity and propose a model circuit to explain how the activity is generated and transmitted to the dorsal horn. Finally, we discuss possible roles of this activity during development and during signal processing under physiological conditions and pain states. By analyzing recent studies on the spontaneous activity of dorsal horn neurons, we aim to shed light on its significance in sensory processing. Understanding the different patterns of activity, the origins of this activity, and the potential roles it may play, will contribute to our knowledge of sensory mechanisms, including pain, to facilitate the modeling of spinal circuits and hopefully to explore novel strategies for pain treatment.
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Affiliation(s)
- Javier Lucas-Romero
- Department of Systems Biology, University of Alcala, 28805, Madrid, Spain
- Department of Physical Therapy, Washington University School of Medicine, Washington University in St. Louis, St. Louis, MO, 63108, USA
| | | | - Jose Antonio Lopez-Garcia
- Department of Systems Biology, University of Alcala, 28805, Madrid, Spain.
- Departamento de Biologia de Sistemas, Edificio de Medicina, Universidad de Alcala, Ctra. Madrid-Barcelona, Km 33,600, 28805, Alcala de Henares, Madrid, Spain.
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Kuo CC, Chan H, Hung WC, Chen RF, Yang HW, Min MY. Carbachol increases locus coeruleus activation by targeting noradrenergic neurons, inhibitory interneurons and inhibitory synaptic transmission. Eur J Neurosci 2023; 57:32-53. [PMID: 36382388 DOI: 10.1111/ejn.15866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 10/11/2022] [Accepted: 11/10/2022] [Indexed: 11/18/2022]
Abstract
The locus coeruleus (LC) consists of noradrenergic (NA) neurons and plays an important role in controlling behaviours. Although much of the knowledge regarding LC functions comes from studying behavioural outcomes upon administration of muscarinic acetylcholine receptor (mAChR) agonists into the nucleus, the exact mechanisms remain unclear. Here, we report that the application of carbachol (CCh), an mAChR agonist, increased the spontaneous action potentials (sAPs) of both LC-NA neurons and local inhibitory interneurons (LC I-INs) in acute brain slices by activating M1/M3 mAChRs (m1/3 AChRs). Optogenetic activation of LC I-INs evoked inhibitory postsynaptic currents (IPSCs) in LC-NA neurons that were mediated by γ-aminobutyric acid type A (GABAA ) and glycine receptors, and CCh application decreased the IPSC amplitude through a presynaptic mechanism by activating M4 mAChRs (m4 AChRs). LC-NA neurons also exhibited spontaneous phasic-like activity (sPLA); CCh application increased the incidence of this activity. This effect of CCh application was not observed with blockade of GABAA and glycine receptors, suggesting that the sPLA enhancement occurred likely because of the decreased synaptic transmission of LC I-INs onto LC-NA neurons by the m4 AChR activation and/or increased spiking rate of LC I-INs by the m1/3 AChR activation, which could lead to fatigue of the synaptic transmission. In conclusion, we report that CCh application, while inhibiting their synaptic transmission, increases sAP rates of LC-NA neurons and LC I-INs. Collectively, these effects provide insight into the cellular mechanisms underlying the behaviour modulations following the administration of muscarinic receptor agonists into the LC reported by the previous studies.
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Affiliation(s)
- Chao-Cheng Kuo
- Department of Life Science, College of Life Science, National Taiwan University, Taipei, Taiwan
| | - Hao Chan
- Department of Life Science, College of Life Science, National Taiwan University, Taipei, Taiwan
| | - Wei-Chen Hung
- Department of Life Science, College of Life Science, National Taiwan University, Taipei, Taiwan
| | - Ruei-Feng Chen
- Department of Life Science, College of Life Science, National Taiwan University, Taipei, Taiwan.,Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan
| | - Hsiu-Wen Yang
- Department of Biomedical Sciences, Chung-Shan Medical University, Taichung, Taiwan.,Department of Medical Research, Chung-Shan Medical University Hospital, Taichung, Taiwan
| | - Ming-Yuan Min
- Department of Life Science, College of Life Science, National Taiwan University, Taipei, Taiwan.,Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan
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Wu RN, Hung WC, Chen CT, Tsai LP, Lai WS, Min MY, Wong SB. Firing activity of locus coeruleus noradrenergic neurons decreases in necdin-deficient mice, an animal model of Prader-Willi syndrome. J Neurodev Disord 2020; 12:21. [PMID: 32727346 PMCID: PMC7389383 DOI: 10.1186/s11689-020-09323-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Accepted: 07/17/2020] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND Prader-Willi syndrome (PWS) is a neurodevelopmental disorder characterized by multiple respiratory, cognitive, endocrine, and behavioral symptoms, such as central apnea, intellectual disabilities, exaggerated stress responses, and temper tantrums. The locus coeruleus noradrenergic system (LC-NE) modulates a diverse range of behaviors, including arousal, learning, pain modulation, and stress-induced negative affective states, which are possibly correlated with the pathogenesis of PWS phenotypes. Therefore, we evaluated the LC-NE neuronal activity of necdin-deficient mice, an animal model of PWS. METHODS Heterozygous necdin-deficient mice (B6.Cg-Ndntm1ky) were bred from wild-type (WT) females to generate WT (+m/+p) and heterozygotes (+m/-p) animals, which were examined of LC-NE neuronal activity, developmental reflexes, and plethysmography. RESULTS On slice electrophysiology, LC-NE neurons of Ndntm1ky mice with necdin deficiency showed significantly decreased spontaneous activities and impaired excitability, which was mediated by enhanced A-type voltage-dependent potassium currents. Ndntm1ky mice also exhibited the neonatal phenotypes of PWS, such as hypotonia and blunt respiratory responses to hypercapnia. CONCLUSIONS LC-NE neuronal firing activity decreased in necdin-deficient mice, suggesting that LC, the primary source of norepinephrine in the central nervous system, is possibly involved in PWS pathogenesis.
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Affiliation(s)
- Rui-Ni Wu
- Department of Pediatrics, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, No. 289, Jiangguo Rd, Xindian Dist, New Taipei City, 23142, Taiwan
| | - Wei-Chen Hung
- Department of Life Science, College of Life Science, National Taiwan University, No. 1, Sec 4, Roosevelt Rd, Taipei, 10617, Taiwan
| | - Ching-Tsuey Chen
- Department of Life Science, College of Life Science, National Taiwan University, No. 1, Sec 4, Roosevelt Rd, Taipei, 10617, Taiwan
| | - Li-Ping Tsai
- Department of Pediatrics, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, No. 289, Jiangguo Rd, Xindian Dist, New Taipei City, 23142, Taiwan
- School of Medicine, Tzu Chi University, No. 701, Sec 3, Jhongyang Rd, Hualien, 97071, Taiwan
| | - Wen-Sung Lai
- Department of Psychology, National Taiwan University, No. 1, Sec 4, Roosevelt Rd, Taipei, 10617, Taiwan
| | - Ming-Yuan Min
- Department of Life Science, College of Life Science, National Taiwan University, No. 1, Sec 4, Roosevelt Rd, Taipei, 10617, Taiwan
| | - Shi-Bing Wong
- Department of Pediatrics, Taipei Tzu Chi Hospital, Buddhist Tzu Chi Medical Foundation, No. 289, Jiangguo Rd, Xindian Dist, New Taipei City, 23142, Taiwan.
- School of Medicine, Tzu Chi University, No. 701, Sec 3, Jhongyang Rd, Hualien, 97071, Taiwan.
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Extracellular Signal-Regulated Kinases Mediate an Autoregulation of GABA B-Receptor-Activated Whole-Cell Current in Locus Coeruleus Neurons. Sci Rep 2020; 10:7869. [PMID: 32398643 PMCID: PMC7217949 DOI: 10.1038/s41598-020-64292-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Accepted: 04/09/2020] [Indexed: 11/09/2022] Open
Abstract
The norepinephrine-releasing neurons in the locus coeruleus (LC) are well known to regulate wakefulness/arousal. They display active firing during wakefulness and a decreased discharge rate during sleep. We have previously reported that LC neurons express large numbers of GABAB receptors (GABABRs) located at peri-/extrasynaptic sites and are subject to tonic inhibition due to the continuous activation of GABABRs by ambient GABA, which is significantly higher during sleep than during wakefulness. In this study, we further showed using western blot analysis that the activation of GABABRs with baclofen could increase the level of phosphorylated extracellular signal-regulated kinase 1 (ERK1) in LC tissue. Recordings from LC neurons in brain slices showed that the inhibition of ERK1/2 with U0126 and FR180204 accelerated the decay of whole-cell membrane current induced by prolonged baclofen application. In addition, the inhibition of ERK1/2 also increased spontaneous firing and reduced tonic inhibition of LC neurons after prolonged exposure to baclofen. These results suggest a new role of GABABRs in mediating ERK1-dependent autoregulation of the stability of GABABR-activated whole-cell current, in addition to its well-known effect on gated potassium channels, to cause a tonic current in LC neurons.
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Cholinergic and glutamatergic transmission at synapses between pedunculopotine tegmental nucleus axonal terminals and A7 catecholamine cell group noradrenergic neurons in the rat. Neuropharmacology 2016; 110:237-250. [PMID: 27422407 DOI: 10.1016/j.neuropharm.2016.07.011] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2015] [Revised: 06/23/2016] [Accepted: 07/11/2016] [Indexed: 11/20/2022]
Abstract
We characterized transmission from the pedunculopotine tegmental nucleus (PPTg), which contains cholinergic and glutamatergic neurons, at synapses with noradrenergic (NAergic) A7 neurons. Injection of an anterograde neuronal tracer, biotinylated-dextran amine, into the PPTg resulted in labeling of axonal terminals making synaptic connection with NAergic A7 neurons. Consistent with this, extracellular stimulation using a train of 10 pulses at 100 Hz evoked both fast and slow excitatory synaptic currents (EPSCs) that were blocked, respectively, by DNQX, a non-N-methyl-d-aspartate receptor blocker, or atropine, a cholinergic muscarinic receptor (mAChR) blocker. Interestingly, many spontaneous-like, but stimulation-dependent, EPSCs, were seen for up to one second after the end of stimulation and were blocked by DNQX and decreased by EGTA-AM, a membrane permeable form of EGTA, showing they are glutamatergic EPSCs causing by asynchronous release of vesicular quanta. Moreover, application of atropine or carbachol, an mAChR agonist, caused, respectively, an increase in the number of asynchronous EPSCs or a decrease in the frequency of miniature EPSCs, showing that mAChRs mediated presynaptic inhibition of glutamatergic transmission of the PPTg onto NAergic A7 neurons. In conclusion, our data show direct synaptic transmission of PPTg afferents onto pontine NAergic neurons that involves cooperation of cholinergic and glutamatergic transmission. This dual-transmitter transmission drives the firing rate of NAergic neurons, which may correlate with axonal and somatic/dendritic release of NA.
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Noradrenergic Locus Coeruleus pathways in pain modulation. Neuroscience 2016; 338:93-113. [PMID: 27267247 DOI: 10.1016/j.neuroscience.2016.05.057] [Citation(s) in RCA: 128] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2016] [Revised: 05/20/2016] [Accepted: 05/27/2016] [Indexed: 12/30/2022]
Abstract
The noradrenergic system is crucial for several activities in the body, including the modulation of pain. As the major producer of noradrenaline (NA) in the central nervous system (CNS), the Locus Coeruleus (LC) is a nucleus that has been studied in several pain conditions, mostly due to its strategic location. Indeed, apart from a well-known descending LC-spinal pathway that is important for pain control, an ascending pathway passing through this nucleus may be responsible for the noradrenergic inputs to higher centers of the pain processing, such as the limbic system and frontal cortices. Thus, the noradrenergic system appears to modulate different components of the pain experience and accordingly, its manipulation has distinct behavioral outcomes. The main goal of this review is to bring together the data available regarding the noradrenergic system in relation to pain, particularly focusing on the ascending and descending LC projections in different conditions. How such findings influence our understanding of these conditions is also discussed.
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Liu CY, Lee ML, Yang CS, Chen CM, Min MY, Yang HW. Morphological and physiological evidence of a synaptic connection between the lateral parabrachial nucleus and neurons in the A7 catecholamine cell group in rats. J Biomed Sci 2015; 22:79. [PMID: 26385355 PMCID: PMC4575445 DOI: 10.1186/s12929-015-0179-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2015] [Accepted: 08/20/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The descending noradrenergic (NAergic) system is one of the important endogenous analgesia systems. It has been suggested that noxious stimuli could activate descending NAergic system; nevertheless, the underlying neuronal circuit remains unclear. As NAergic neurons in the A7 catecholamine cell group (A7) are a part of the descending NAergic system and the lateral parabrachial nucleus (LPB) is an important brainstem structure that relays ascending nociceptive signal, we aimed to test whether LPB neurons have direct synaptic contact with NAergic A7 neurons. RESULTS Stereotaxic injections of an anterograde tracer, biotinylated dextran-amine (BDA), were administered to LPB in rats. The BDA-labeled axonal terminals that have physical contacts with tyrosine hydroxylase-positive (presumed noadrenergic) neurons were identified in A7. Consistent with these morphological observations, the excitatory synaptic currents (EPSCs) were readily evoked in NAergic A7 neurons by extracellular stimulation of LPB. The EPSCs evoked by LPB stimulation were blocked by CNQX, a non-NMDA receptor blocker, and AP5, a selective NMDA receptor blocker, showing that LPB-A7 synaptic transmission is glutamatergic. Moreover, the amplitude of LPB-A7 EPSCs was significantly attenuated by DAMGO, a selective μ-opioid receptor agonist, which was associated with an increase in paired-pulse ratio. CONCLUSIONS Taken together, the above results showed direct synaptic connections between LPB and A7 catecholamine cell group, the function of which is subject to presynaptic modulation by μ-opioid receptors.
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Affiliation(s)
- Chia-Yi Liu
- Department of Life Sciences, and Agricultural Biotechnology Center, National Chung Hsing University, Taichung, Taiwan. .,Department of Nursing, Jen-Teh Junior College of Medicine, Nursing and Management, Miaoli, Taiwan.
| | - Meng-Lam Lee
- Department of Biomedical Sciences, Chung Shan Medical University, 110, Chien-Kuo N. Rd, Sec. 1, Taichung, 402, Taiwan. .,Department of Medical Research, Chung Shan Medical University, Taichung, Taiwan.
| | - Chi-Sheng Yang
- Department of Nursing, Hungkuang University, Taichung, Taiwan.
| | - Chuan-Mu Chen
- Department of Life Sciences, and Agricultural Biotechnology Center, National Chung Hsing University, Taichung, Taiwan. .,Rong Hsing Research Center for Translational Medicine, and the iEGG Center, National Chung Hsing University, Taichung, Taiwan.
| | - Ming-Yuan Min
- Department of Life Sciences, College of Life Science, National Taiwan University, Taipei, Taiwan.
| | - Hsiu-Wen Yang
- Department of Biomedical Sciences, Chung Shan Medical University, 110, Chien-Kuo N. Rd, Sec. 1, Taichung, 402, Taiwan. .,Department of Medical Research, Chung Shan Medical University, Taichung, Taiwan.
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Wang HY, Kuo ZC, Fu YS, Chen RF, Min MY, Yang HW. GABAB receptor-mediated tonic inhibition regulates the spontaneous firing of locus coeruleus neurons in developing rats and in citalopram-treated rats. J Physiol 2014; 593:161-80. [PMID: 25556794 DOI: 10.1113/jphysiol.2014.281378] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Accepted: 09/30/2014] [Indexed: 12/17/2022] Open
Abstract
KEY POINTS Noradrenaline (NA)-releasing neurons in the locus coeruleus (LC) provide NA to the forebrain and play important roles in regulating many brain functions. LC neurons are subject to tonic inhibition mediated by GABAB receptors (GABAB Rs) and that the extent of the effect varies with ambient GABA levels. GABAB R-mediated tonic inhibition can effectively tune the spontaneous firing rate (SFR) of LC neurons; it is developmentally regulated and is responsible for maintaining a constant SFR of LC neurons during development. In male, but not female rats, chronic perinatal treatment with citalopram, a selective serotonin reuptake inhibitor, results in downregulation of GABAB R-mediated tonic inhibition of LC neurons that partially accounts for increased SFR in male, but not female, rats receiving such treatment. Our results show that GABAB R-mediated tonic inhibition could be an important player in the development of normal and abnormal behaviours/brain functions associated with the LC-NA system. Noradrenaline (NA)-releasing neurons in the locus coeruleus (LC) provide NA to the forebrain. Their activity is believed to be a key factor regulating the wakefulness/arousal level of the brain. In this study, we found that the activity of NA-releasing neurons in the LC (LC neurons) was subject to γ-aminobutyric acid (GABA) tonic inhibition through GABAB receptors (GABAB Rs), but not GABAA receptors. The intensity of GABAB R tonic inhibition was found to depend on ambient GABA levels, as it was dramatically increased by blockade of GABA reuptake. It also varied with the function of GABAB Rs. The GABAB R activity on LC neurons was found to increase with postnatal age up to postnatal days 8-10, resulting in increased tonic inhibition. Interestingly, there was no significant difference in the spontaneous activity of LC neurons at different postnatal ages unless GABAB R tonic inhibition was blocked. These results show that, during postnatal development, there is a continuous increase in GABAB R tonic inhibition that maintains the activity of LC neurons at a proper level. In male, but not female, rats, chronic perinatal treatment with citalopram, a selective serotonin reuptake inhibitor, reduced GABAB R activity and tonic inhibition, which might result in the significantly higher spontaneous activity of LC neurons seen in these animals. In conclusion, our results show that GABAB R-mediated tonic inhibition has a direct impact on the spontaneous activity of LC neurons and that the extent of the effect varies with ambient GABA levels and functionality of GABAB R signalling.
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Affiliation(s)
- Han-Ying Wang
- Institute of Zoology, National Taiwan University, Taipei, 107, Taiwan; Department of Life Science, National Taiwan University, Taipei, 107, Taiwan
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Jeong Y, Moes JR, Wagner M, Holden JE. The posterior hypothalamus exerts opposing effects on nociception via the A7 catecholamine cell group in rats. Neuroscience 2012; 227:144-53. [PMID: 23036619 DOI: 10.1016/j.neuroscience.2012.09.058] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Revised: 09/19/2012] [Accepted: 09/22/2012] [Indexed: 01/16/2023]
Abstract
Stimulation of the posterior hypothalamic area (PH) produces antinociception in rats and humans, but the precise mechanisms are unknown. The PH forms anatomical connections with the parabrachial area, which contains the pontine A7 catecholamine cell group, a group of spinally projecting noradrenergic neurons known to produce antinociception in the dorsal horn. The aim of the present study was to determine whether PH-induced antinociception is mediated in part through connections with the A7 cell group in female Sprague-Dawley rats, as measured by the tail flick and foot withdrawal latency. Stimulation of the PH with the cholinergic agonist carbachol (125 nmol) produced antinociception that was blocked by pretreatment with atropine sulfate. Intrathecal injection of the α(2)-adrenoceptor antagonist yohimbine reversed PH-induced antinociception, but the α(1)-adrenoceptor antagonist WB4101 facilitated antinociception. Intrathecal injection of normal saline had no effect. In a separate experiment, cobalt chloride, which reversibly arrests synaptic activity, was microinjected into the A7 cell group and blocked PH-induced antinociception. These findings provide evidence that the PH modulates nociception in part through connections with the A7 catecholamine cell group through opposing effects. Antinociception occurs from actions at α(2)-adrenoceptors in the dorsal horn, while concurrent hyperalgesia occurs from actions of norepinephrine at α(1)-adrenoceptors. This hyperalgesic response likely attenuates antinociception from PH stimulation.
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Affiliation(s)
- Y Jeong
- College of Nursing Science, Kyung Hee University, 26 Kyunghee-daero, Dongdaemun-gu, Seoul 130-701, Korea.
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Kanyshkova T, Broicher T, Meuth SG, Pape HC, Budde T. A-type K+ currents in intralaminar thalamocortical relay neurons. Pflugers Arch 2011; 461:545-56. [PMID: 21437601 DOI: 10.1007/s00424-011-0953-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2011] [Accepted: 02/22/2011] [Indexed: 10/18/2022]
Abstract
Transient A-type K+ currents (I(A)) are known to influence the firing pattern of a number of thalamic cell types, but have not been investigated in intralaminar thalamocortical (TC) relay neurons yet. We therefore combined whole-cell patch-clamp techniques, PCR analysis, and immunohistochemistry to investigate the voltage-dependent and pharmacological properties of I(A) and to determine its molecular basis in TC neurons from the centrolateral, paracentral, and centromedial thalamic nuclei. I(A) revealed half-maximal (V (h)) activation and inactivation at about -17 and -67 mV, respectively. At a concentration of 5-10 mM 4-aminopyridine (4-AP) completely blocked I(A). Furthermore, I(A) was nearly unaffected by two sea anemone toxins (blood depressing substances 1 and 2, BDS1 and BDS2; 6-8% block at a concentration of 1 μM) but strongly sensitive to the K(V)4 channel blocker Heteropoda venatoria toxin 2 (HpTx2; about 45% block at a concentration of 5 μM). PCR screening revealed the expression of K(V)4.1-4.3, with strongest expression for K(V)4.2 and weak expression for K(V)4.1. Accordingly K(V)4.1 was not detected in immunohistochemical staining. Furthermore, K(V)4.2 and K(V)4.3 revealed mainly dendritic and somatic staining, respectively. Together with current clamp recordings, these findings point to a scenario where the fast transient I(A) in intralaminar TC neurons has a depolarized threshold at potentials negative to -50 mV, is substantially generated by K(V)4.2 and K(V)4.3 channels, allows prominent burst firing at hyperpolarized potentials, prevents the generation of high-threshold potentials, generates a delayed onset of firing at more depolarized potentials, and allows fast tonic firing.
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Affiliation(s)
- Tatyana Kanyshkova
- Institute of Physiology I, Westfälische Wilhelms-Universität, Robert-Koch-Str. 27a, 48149, Münster, Germany
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Wu Y, Wang HY, Lin CC, Lu HC, Cheng SJ, Chen CC, Yang HW, Min MY. GABAB receptor-mediated tonic inhibition of noradrenergic A7 neurons in the rat. J Neurophysiol 2011; 105:2715-28. [PMID: 21430282 DOI: 10.1152/jn.00459.2010] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Noradrenergic (NAergic) A7 neurons that project axonal terminals to the dorsal horn of the spinal cord to modulate nociceptive signaling are suggested to receive tonic inhibition from local GABAergic interneurons, which are under the regulation of descending analgesic pathways. In support of this argument, we presently report GABA(B) receptor (GABA(B)R)-mediated tonic inhibition of NAergic A7 neurons. Bath application of baclofen induced an outward current (I(Bac)) in NAergic A7 neurons that was blocked by CGP 54626, a GABA(B)R blocker. The I(Bac) was reversed at about -99 mV, displayed inward rectification, and was blocked by Ba(2+) or Tertipian-Q, showing it was mediated by G protein-activated inward-rectifying K(+) (GIRK) channels. Single-cell RT-PCR results suggested that GIRK1/3 heterotetramers might dominate functional GIRK channels in NAergic A7 neurons. Under conditions in which GABA(A) and glycine receptors were blocked, bath application of GABA inhibited the spontaneous firing of NAergic A7 neurons in a dose-dependent manner. Interestingly, CGP 54626 application not only blocked the effect of GABA but also increased the firing rate to 126.9% of the control level, showing that GABA(B)Rs were constitutively active at an ambient GABA concentration of 2.8 μM and inhibited NAergic A7 neurons. GABA(B)Rs were also found at presynaptic excitatory and inhibitory axonal terminals in the A7 area. Pharmacological activation of these GABA(B)Rs inhibited the release of neurotransmitters. No physiological role was found for GABA(B)Rs on excitatory terminals, whereas those on the inhibitory terminals were found to exert autoregulatory control of GABA release.
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Affiliation(s)
- Yeechan Wu
- Institute of Zoology, College of Life Science, National Taiwan University, Taipei, Taiwan
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