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Mohammadalinejad G, Afsharipour B, Yacyshyn A, Duchcherer J, Bashuk J, Bennett E, Pearcey GEP, Negro F, Quinlan KA, Bennett DJ, Gorassini MA. Intrinsic motoneuron properties in typical human development. J Physiol 2024; 602:2061-2087. [PMID: 38554126 DOI: 10.1113/jp285756] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Accepted: 03/06/2024] [Indexed: 04/01/2024] Open
Abstract
Motoneuron properties and their firing patterns undergo significant changes throughout development and in response to neuromodulators such as serotonin. Here, we examined the age-related development of self-sustained firing and general excitability of tibialis anterior motoneurons in a young development (7-17 years), young adult (18-28 years) and adult (32-53 years) group, as well as in a separate group of participants taking selective serotonin reuptake inhibitors (SSRIs, aged 11-28 years). Self-sustained firing, as measured by ΔF, was larger in the young development (∼5.8 Hz, n = 20) compared to the young adult (∼4.9 Hz, n = 13) and adult (∼4.8 Hz, n = 8) groups, consistent with a developmental decrease in self-sustained firing mediated by persistent inward currents (PIC). ΔF was also larger in participants taking SSRIs (∼6.5 Hz, n = 9) compared to their age-matched controls (∼5.3 Hz, n = 26), consistent with increased levels of spinal serotonin facilitating the motoneuron PIC. Participants in the young development and SSRI groups also had higher firing rates and a steeper acceleration in initial firing rates (secondary ranges), consistent with the PIC producing a steeper acceleration in membrane depolarization at the onset of motoneuron firing. In summary, both the young development and SSRI groups exhibited increased intrinsic motoneuron excitability compared to the adults, which, in the young development group, was also associated with a larger unsteadiness in the dorsiflexion torque profiles. We propose several intrinsic and extrinsic factors that affect both motoneuron PICs and cell discharge which vary during development, with a time course similar to the changes in motoneuron firing behaviour observed in the present study. KEY POINTS: Neurons in the spinal cord that activate muscles in the limbs (motoneurons) undergo increases in excitability shortly after birth to help animals stand and walk. We examined whether the excitability of human ankle flexor motoneurons also continues to change from child to adulthood by recording the activity of the muscle fibres they innervate. Motoneurons in children and adolescents aged 7-17 years (young development group) had higher signatures of excitability that included faster firing rates and more self-sustained activity compared to adults aged ≥18 years. Participants aged 11-28 years of age taking serotonin reuptake inhibitors had the highest measures of motoneuron excitability compared to their age-matched controls. The young development group also had more unstable contractions, which might partly be related to the high excitability of the motoneurons.
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Affiliation(s)
- Ghazaleh Mohammadalinejad
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Babak Afsharipour
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
| | - Alex Yacyshyn
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jennifer Duchcherer
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Jack Bashuk
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Erin Bennett
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
| | - Gregory E P Pearcey
- School of Human Kinetics and Recreation, Memorial University of Newfoundland, St John's Canada and Physical Therapy & Human Movement Sciences, Northwestern University, Chicago, IL, USA
| | - Francesco Negro
- Clinical and Experimental Sciences, Universita degli Studi di Brescia, Brescia, Italia
| | - Katharina A Quinlan
- George and Anne Ryan Institute for Neuroscience, Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - David J Bennett
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Faculty of Rehabilitation Medicine, University of Alberta, Edmonton, AB, Canada
| | - Monica A Gorassini
- Department of Medicine, Faculty of Medicine and Dentistry, University of Alberta, Edmonton, AB, Canada
- Neuroscience and Mental Health Institute, University of Alberta, Edmonton, AB, Canada
- Women and Children's Health Research Institute, University of Alberta, Edmonton, AB, Canada
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REEDICH EJ, GENRY L, STEELE P, AVILA EMENA, DOWALIBY L, DROBYSHEVSKY A, MANUEL M, QUINLAN KA. Spinal motoneurons respond aberrantly to serotonin in a rabbit model of cerebral palsy. J Physiol 2023; 601:4271-4289. [PMID: 37584461 PMCID: PMC10543617 DOI: 10.1113/jp284803] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 07/24/2023] [Indexed: 08/17/2023] Open
Abstract
Cerebral palsy (CP) is caused by a variety of factors that damage the developing central nervous system. Impaired motor control, including muscle stiffness and spasticity, is the hallmark of spastic CP. Rabbits that experience hypoxic-ischaemic (HI) injury in utero (at 70%-83% gestation) are born with muscle stiffness, hyperreflexia and, as recently discovered, increased 5-HT in the spinal cord. To determine whether serotonergic modulation of spinal motoneurons (MNs) contributes to motor deficits, we performed ex vivo whole cell patch clamp in neonatal rabbit spinal cord slices at postnatal day (P) 0-5. HI MNs responded to the application of α-methyl 5-HT (a 5-HT1 /5-HT2 receptor agonist) and citalopram (a selective 5-HT reuptake inhibitor) with increased amplitude and hyperpolarization of persistent inward currents and hyperpolarized threshold voltage for action potentials, whereas control MNs did not exhibit any of these responses. Although 5-HT similarly modulated MN properties of HI motor-unaffected and motor-affected kits, it affected sag/hyperpolarization-activated cation current (Ih ) and spike frequency adaptation only in HI motor-affected MNs. To further explore the differential sensitivity of MNs to 5-HT, we performed immunostaining for inhibitory 5-HT1A receptors in lumbar spinal MNs at P5. Fewer HI MNs expressed the 5-HT1A receptor compared to age-matched control MNs. This suggests that HI MNs may lack a normal mechanism of central fatigue, mediated by 5-HT1A receptors. Altered expression of other 5-HT receptors (including 5-HT2 ) likely also contributes to the robust increase in HI MN excitability. In summary, by directly exciting MNs, the increased concentration of spinal 5-HT in HI-affected rabbits can cause MN hyperexcitability, muscle stiffness and spasticity characteristic of CP. Therapeutic strategies that target serotonergic neuromodulation may be beneficial to individuals with CP. KEY POINTS: We used whole cell patch clamp electrophysiology to test the responsivity of spinal motoneurons (MNs) from neonatal control and hypoxia-ischaemia (HI) rabbits to 5-HT, which is elevated in the spinal cord after prenatal HI injury. HI rabbit MNs showed a more robust excitatory response to 5-HT than control rabbit MNs, including hyperpolarization of the persistent inward current and threshold voltage for action potentials. Although most MN properties of HI motor-unaffected and motor-affected kits responded similarly to 5-HT, 5-HT caused larger sag/hyperpolarization-activated cation current (Ih ) and altered repetitive firing patterns only in HI motor-affected MNs. Immunostaining revealed that fewer lumbar MNs expressed inhibitory 5-HT1A receptors in HI rabbits compared to controls, which could account for the more robust excitatory response of HI MNs to 5-HT. These results suggest that elevated 5-HT after prenatal HI injury could trigger a cascade of events that lead to muscle stiffness and altered motor unit development.
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Affiliation(s)
- E. J. REEDICH
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - L.T. GENRY
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - P.R. STEELE
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - E. MENA AVILA
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - L. DOWALIBY
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | | | - M. MANUEL
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - K. A. QUINLAN
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
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REEDICH EJ, GENRY L, STEELE P, AVILA EMENA, DOWALIBY L, DROBYSHEVSKY A, MANUEL M, QUINLAN KA. Spinal motoneurons respond aberrantly to serotonin in a rabbit model of cerebral palsy. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.05.535691. [PMID: 37066318 PMCID: PMC10104065 DOI: 10.1101/2023.04.05.535691] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
Abstract
Cerebral palsy (CP) is caused by a variety of factors that damage the developing central nervous system. Impaired motor control, including muscle stiffness and spasticity, is the hallmark of spastic CP. Rabbits that experience hypoxic-ischemic (HI) injury in utero (at 70-80% gestation) are born with muscle stiffness, hyperreflexia, and, as recently discovered, increased serotonin (5-HT) in the spinal cord. To determine whether serotonergic modulation of spinal motoneurons (MNs) contributes to motor deficits, we performed ex vivo whole cell patch clamp in neonatal rabbit spinal cord slices at postnatal day (P) 0-5. HI MNs responded to application of α-methyl 5-HT (a 5-HT 1 /5-HT 2 receptor agonist) and citalopram (a selective 5-HT reuptake inhibitor) with hyperpolarization of persistent inward currents and threshold voltage for action potentials, reduced maximum firing rate, and an altered pattern of spike frequency adaptation while control MNs did not exhibit any of these responses. To further explore the differential sensitivity of MNs to 5-HT, we performed immunohistochemistry for inhibitory 5-HT 1A receptors in lumbar spinal MNs at P5. Fewer HI MNs expressed the 5-HT 1A receptor compared to age-matched controls. This suggests many HI MNs lack a normal mechanism of central fatigue mediated by 5-HT 1A receptors. Other 5-HT receptors (including 5-HT 2 ) are likely responsible for the robust increase in HI MN excitability. In summary, by directly exciting MNs, the increased concentration of spinal 5-HT in HI rabbits can cause MN hyperexcitability, muscle stiffness, and spasticity characteristic of CP. Therapeutic strategies that target serotonergic neuromodulation may be beneficial to individuals with CP. Key points After prenatal hypoxia-ischemia (HI), neonatal rabbits that show hypertonia are known to have higher levels of spinal serotoninWe tested responsivity of spinal motoneurons (MNs) in neonatal control and HI rabbits to serotonin using whole cell patch clampMNs from HI rabbits showed a more robust excitatory response to serotonin than control MNs, including hyperpolarization of the persistent inward current and threshold for action potentials, larger post-inhibitory rebound, and less spike frequency adaptation Based on immunohistochemistry of lumbar MNs, fewer HI MNs express inhibitory 5HT 1A receptors than control MNs, which could account for the more robust excitatory response of HI MNs. These results suggest that after HI injury, the increased serotonin could trigger a cascade of events leading to muscle stiffness and altered motor unit development.
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Affiliation(s)
- E. J. REEDICH
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - L.T. GENRY
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - P.R. STEELE
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - E. MENA AVILA
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | - L. DOWALIBY
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
| | | | - M. MANUEL
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
| | - K. A. QUINLAN
- George and Anne Ryan Institute for Neuroscience, University of Rhode Island, Kingston, RI, USA
- Department of Biomedical and Pharmaceutical Sciences, College of Pharmacy, University of Rhode Island, Kingston, RI, USA
- Interdisciplinary Neuroscience Program, University of Rhode Island, Kingston, RI, USA
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Cholinergic modulation of persistent inward currents is mediated by activating muscarinic receptors of serotonergic neurons in the brainstem of ePet-EYFP mice. Exp Brain Res 2022; 240:1177-1189. [PMID: 35166863 DOI: 10.1007/s00221-022-06322-w] [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: 07/21/2021] [Accepted: 02/02/2022] [Indexed: 11/04/2022]
Abstract
Persistent inward currents (PICs) play important roles in regulating neural excitability. Results from our previous studies showed that serotonergic (5-HT) neurons of the brainstem expressed PICs. However, little is known about cholinergic (ACh) modulation of PICs in the 5-HT neurons. The whole-cell patch-clamp recordings were performed in the brainstem slices of ePet-EYFP mice to investigate the electrophysiological properties of PICs with cholinergic modulation. PICs in 5-HT neurons were activated at - 51.4 ± 3.7 mV with the amplitude of - 171.6 ± 48.9 pA (n = 71). Bath application of 20-25 μM ACh increased the amplitude by 79.1 ± 42.5 pA (n = 23, p < 0.001) and hyperpolarized the onset voltage by 2.2 ± 2.7 mV (n = 23, p < 0.01) and half-maximal activation by 3.6 ± 2.7 mV (n = 6, p < 0.01). Muscarine mimicked the effects of ACh on PICs, while bath application of nicotine (15-20 μM) did not induce substantial change in the PICs (n = 9). Muscarine enhanced the amplitude of PICs by 100.0 ± 27.4 pA (n = 28, p < 0.001) and lowered the onset voltage by 2.8 ± 1.2 mV (n = 28, p < 0.001) and the half-maximal activation by 2.9 ± 1.4 mV. ACh-induced increase of amplitude and hyperpolarization of onset voltage were blocked by 3-5 μM atropine. Furthermore, the muscarine-induced enhancement of the PICs was antagonized by 5 μM 4-DAMP, the antagonist of M3 receptor, while the antagonists of M1 (Telenzepine, 5 μM) and M5 (VU6008667, 5 μM) receptors did not significantly affect the PIC enhancement. This study suggested that ACh potentiated PICs in 5-HT neurons of the brainstem by activating muscarinic M3 receptor.
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Sharples SA, Miles GB. Maturation of persistent and hyperpolarization-activated inward currents shapes the differential activation of motoneuron subtypes during postnatal development. eLife 2021; 10:e71385. [PMID: 34783651 PMCID: PMC8641952 DOI: 10.7554/elife.71385] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2021] [Accepted: 11/15/2021] [Indexed: 12/15/2022] Open
Abstract
The size principle underlies the orderly recruitment of motor units; however, motoneuron size is a poor predictor of recruitment amongst functionally defined motoneuron subtypes. Whilst intrinsic properties are key regulators of motoneuron recruitment, the underlying currents involved are not well defined. Whole-cell patch-clamp electrophysiology was deployed to study intrinsic properties, and the underlying currents, that contribute to the differential activation of delayed and immediate firing motoneuron subtypes. Motoneurons were studied during the first three postnatal weeks in mice to identify key properties that contribute to rheobase and may be important to establish orderly recruitment. We find that delayed and immediate firing motoneurons are functionally homogeneous during the first postnatal week and are activated based on size, irrespective of subtype. The rheobase of motoneuron subtypes becomes staggered during the second postnatal week, which coincides with the differential maturation of passive and active properties, particularly persistent inward currents. Rheobase of delayed firing motoneurons increases further in the third postnatal week due to the development of a prominent resting hyperpolarization-activated inward current. Our results suggest that motoneuron recruitment is multifactorial, with recruitment order established during postnatal development through the differential maturation of passive properties and sequential integration of persistent and hyperpolarization-activated inward currents.
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Affiliation(s)
- Simon A Sharples
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
| | - Gareth B Miles
- School of Psychology and Neuroscience, University of St AndrewsSt AndrewsUnited Kingdom
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Dey S, Surendran D, Engberg O, Gupta A, Fanibunda SE, Das A, Maity BK, Dey A, Visvakarma V, Kallianpur M, Scheidt HA, Walker G, Vaidya VA, Huster D, Maiti S. Altered Membrane Mechanics Provides a Receptor-Independent Pathway for Serotonin Action. Chemistry 2021; 27:7533-7541. [PMID: 33502812 PMCID: PMC8252079 DOI: 10.1002/chem.202100328] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2021] [Indexed: 12/20/2022]
Abstract
Serotonin, an important signaling molecule in humans, has an unexpectedly high lipid membrane affinity. The significance of this finding has evoked considerable speculation. Here we show that membrane binding by serotonin can directly modulate membrane properties and cellular function, providing an activity pathway completely independent of serotonin receptors. Atomic force microscopy shows that serotonin makes artificial lipid bilayers softer, and induces nucleation of liquid disordered domains inside the raft‐like liquid‐ordered domains. Solid‐state NMR spectroscopy corroborates this data at the atomic level, revealing a homogeneous decrease in the order parameter of the lipid chains in the presence of serotonin. In the RN46A immortalized serotonergic neuronal cell line, extracellular serotonin enhances transferrin receptor endocytosis, even in the presence of broad‐spectrum serotonin receptor and transporter inhibitors. Similarly, it increases the membrane binding and internalization of oligomeric peptides. Our results uncover a mode of serotonin–membrane interaction that can potentiate key cellular processes in a receptor‐independent fashion.
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Affiliation(s)
- Simli Dey
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Dayana Surendran
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Oskar Engberg
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, 04107, Leipzig, Germany
| | - Ankur Gupta
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Sashaina E Fanibunda
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India.,Kasturba Health Society, Medical Research Center, Mumbai, India
| | - Anirban Das
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Barun Kumar Maity
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Arpan Dey
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Vicky Visvakarma
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Mamata Kallianpur
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Holger A Scheidt
- Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, 04107, Leipzig, Germany
| | - Gilbert Walker
- Department of Chemistry, University of Toronto, Toronto, Ontario, M5S3H6, Canada
| | - Vidita A Vaidya
- Department of Biological Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
| | - Daniel Huster
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India.,Institute of Medical Physics and Biophysics, University of Leipzig, Härtelstr. 16-18, 04107, Leipzig, Germany
| | - Sudipta Maiti
- Department of Chemical Sciences, Tata Institute of Fundamental Research, Homi Bhabha Road, Colaba, Mumbai, 400005, India
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Cheng Y, Song N, Ge R, Dai Y. Serotonergic Modulation of Persistent Inward Currents in Serotonergic Neurons of Medulla in ePet-EYFP Mice. Front Neural Circuits 2021; 15:657445. [PMID: 33889077 PMCID: PMC8055846 DOI: 10.3389/fncir.2021.657445] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 03/15/2021] [Indexed: 11/23/2022] Open
Abstract
Serotonergic (5-HT) neurons in the medulla play multiple functional roles associated with many symptoms and motor activities. The descending serotonergic pathway from medulla is essential for initiating locomotion. However, the ionic properties of 5-HT neurons in the medulla remain unclear. Using whole-cell patch-clamp technique, we studied the biophysical and modulatory properties of persistent inward currents (PICs) in 5-HT neurons of medulla in ePet-EYFP transgenic mice (P3–P6). PICs were recorded by a family of voltage bi-ramps (10-s duration, 40-mV peak step), and the ascending and descending PICs were mirrored to analyze the PIC hysteresis. PICs were found in 77% of 5-HT neurons (198/258) with no significant difference between parapyramidal region (n = 107) and midline raphe nuclei (MRN) (n = 91) in either PIC onset (−47.4 ± 10 mV and −48.7 ± 7 mV; P = 0.44) or PIC amplitude (226.9 ± 138 pA and 259.2 ± 141 pA; P = 0.29). Ninety-six percentage (191/198) of the 5-HT neurons displayed counterclockwise hysteresis and four percentage (7/198) exhibited the clockwise hysteresis. The composite PICs could be differentiated as calcium component (Ca_PIC) by bath application of nimodipine (25 μM), sodium component (Na_PIC) by tetrodotoxin (TTX, 2 μM), and TTX- and dihydropyridine-resistance component (TDR_PIC) by TTX and nimodipine. Ca_PIC, Na_PIC and TDR_PIC all contributed to upregulation of excitability of 5-HT neurons. 5-HT (15 μM) enhanced the PICs, including a 26% increase in amplitude of the compound currents of Ca_PIC and TDR_PIC (P < 0.001, n = 9), 3.6 ± 5 mV hyperpolarization of Na_PIC and TDR_PIC onset (P < 0.05, n = 12), 30% increase in amplitude of TDR_PIC (P < 0.01), and 2.0 ± 3 mV hyperpolarization of TDR_PIC onset (P < 0.05, n = 18). 5-HT also facilitated repetitive firing of 5-HT neurons through modulation of composite PIC, Na_PIC and TDR_PIC, and Ca_PIC and TDR_PIC, respectively. In particular, the high voltage-activated TDR_PIC facilitated the repetitive firing in higher membrane potential, and this facilitation could be amplified by 5-HT. Morphological data analysis indicated that the dendrites of 5-HT neurons possessed dense spherical varicosities intensively crossing 5-HT neurons in medulla. We characterized the PICs in 5-HT neurons and unveiled the mechanism underlying upregulation of excitability of 5-HT neurons through serotonergic modulation of PICs. This study provided insight into channel mechanisms responsible for the serotonergic modulation of serotonergic neurons in brainstem.
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Affiliation(s)
- Yi Cheng
- School of Physical Education, Yunnan University, Kunming, China
| | - Nan Song
- Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, School of Physical Education and Health Care, East China Normal University, Shanghai, China
| | - Renkai Ge
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, China.,School of Physical Education and Health Care, East China Jiaotong University, Nanchang, China
| | - Yue Dai
- Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, School of Physical Education and Health Care, East China Normal University, Shanghai, China.,Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, China
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da Silva MP, Magalhães KS, de Souza DP, Moraes DJA. Chronic intermittent hypoxia increases excitability and synaptic excitation of protrudor and retractor hypoglossal motoneurones. J Physiol 2021; 599:1917-1932. [PMID: 33507557 DOI: 10.1113/jp280788] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2020] [Accepted: 01/11/2021] [Indexed: 12/13/2022] Open
Abstract
KEY POINTS Dysfunctions in the hypoglossal control of tongue extrinsic muscles are implicated in obstructive sleep apnoea (OSA) syndrome. Chronic intermittent hypoxia (CIH), an important feature of OSA syndrome, produces deleterious effects on the motor control of oropharyngeal resistance, but whether the hypoglossal motoneurones innervating the tongue extrinsic muscles are affected by CIH is unknown. We show that CIH enhanced the respiratory-related activity of rat hypoglossal nerve innervating the protrudor and retractor tongue extrinsic muscles. Intracellular recordings revealed increases in respiratory-related firing frequency and synaptic excitation of inspiratory protrudor and retractor hypoglossal motoneurones after CIH. CIH also increased their intrinsic excitability, depolarised resting membrane potential and reduced K+ -dominated leak conductance. CIH affected the breathing-related synaptic control and intrinsic electrophysiological properties of protrudor and retractor hypoglossal motoneurones to optimise the neural control of oropharyngeal function. ABSTRACT Inspiratory-related tongue movements and oropharyngeal motor actions are controlled mainly by the protrudor and retractor extrinsic tongue muscles, which are innervated by the hypoglossal motoneurones. Chronic intermittent hypoxia (CIH), an important feature of obstructive sleep apnoea syndrome, produces detrimental effects on the contractile function of the tongue extrinsic muscles and the medullary inspiratory network of rodents. However, the impact of the CIH on the electrophysiological properties of protrudor and retractor hypoglossal motoneurones has not been described before. Using nerves and intracellular recordings in in situ preparation of rats (5 weeks old), we tested the hypothesis that CIH (FiO2 of 0.06, SaO2 74%, during 30-40 s, every 9 min, 8 h/day for 10 days) increases the intrinsic excitability of protrudor and retractor motoneurones from the hypoglossal motor nucleus of rats. Recordings of hypoglossal nerve, before its bifurcation to innervate the tongue protrudor and retractor muscles, revealed that CIH enhances its pre-inspiratory, simultaneously with the presence of active expiration, and inspiratory activities. These changes were mediated by increases in the respiratory-related firing frequency and synaptic excitation of inspiratory protrudor and retractor hypoglossal motoneurones. Besides, CIH increases their intrinsic excitability and depolarises resting membrane potential by reducing a K+ -dominated leak conductance. In conclusion, CIH enhances the respiratory-related neural control of oropharyngeal function of rats by increasing the synaptic excitation, intrinsic excitability, and reducing leak conductance in both protrudor and retractor hypoglossal motoneurones. We propose that these network and cellular changes are important to optimise the oropharyngeal resistance in conditions related to intermittent hypoxia.
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Affiliation(s)
- Melina P da Silva
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Karolyne S Magalhães
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Daniel P de Souza
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
| | - Davi J A Moraes
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Ribeirão Preto, SP, Brazil
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Ge R, Dai Y. Three-Week Treadmill Exercise Enhances Persistent Inward Currents, Facilitates Dendritic Plasticity, and Upregulates the Excitability of Dorsal Raphe Serotonin Neurons in ePet-EYFP Mice. Front Cell Neurosci 2020; 14:575626. [PMID: 33177992 PMCID: PMC7595958 DOI: 10.3389/fncel.2020.575626] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2020] [Accepted: 09/04/2020] [Indexed: 12/14/2022] Open
Abstract
Exercise plays a key role in preventing or treating mental or motor disorders caused by dysfunction of the serotonergic system. However, the electrophysiological and ionic channel mechanisms underlying these effects remain unclear. In this study, we investigated the effects of 3-week treadmill exercise on the electrophysiological and channel properties of dorsal raphe nucleus (DRN). Serotonin (5-HT) neurons in ePet-EYFP mice, using whole-cell patch clamp recording. Treadmill exercise was induced in ePet-EYFP mice of P21–24 for 3 weeks, and whole-cell patch clamp recording was performed on EYFP-positive 5-HT neurons from DRN slices of P42–45 mice. Experiment data showed that 5-HT neurons in the DRN were a heterogeneous population with multiple firing patterns (single firing, phasic firing, and tonic firing). Persistent inward currents (PICs) with multiple patterns were expressed in 5-HT neurons and composed of Cav1.3 (Ca-PIC) and sodium (Na-PIC) components. Exercise hyperpolarized the voltage threshold for action potential (AP) by 3.1 ± 1.0 mV (control: n = 14, exercise: n = 18, p = 0.005) and increased the AP amplitude by 6.7 ± 3.0 mV (p = 0.031) and firing frequency by more than 22% especially within a range of current stimulation stronger than 70 pA. A 3-week treadmill exercise was sufficient to hyperpolarize PIC onset by 2.6 ± 1.3 mV (control: −53.4 ± 4.7 mV, n = 28; exercise: −56.0 ± 4.7 mV, n = 25, p = 0.050) and increase the PIC amplitude by 28% (control: 193.6 ± 81.8 pA; exercise: 248.5 ± 105.4 pA, p = 0.038). Furthermore, exercise hyperpolarized Na-PIC onset by 3.8 ± 1.8 mV (control: n = 8, exercise: n = 9, p = 0.049) and increased the Ca-PIC amplitude by 23% (p = 0.013). The exercise-induced enhancement of the PIC amplitude was mainly mediated by Ca-PIC and hyperpolarization of PIC onset by Na-PIC. Moreover, exercise facilitated dendritic plasticity, which was shown as the increased number of branch points by 1.5 ± 0.5 (p = 0.009) and dendritic branches by 2.1 ± 0.6 (n = 20, p = 0.001) and length by 732.0 ± 100.1 μm (p < 0.001) especially within the range of 50–200 μm from the soma. Functional analysis suggested that treadmill exercise enhanced Na-PIC for facilitation of spike initiation and Ca-PIC for regulation of repetitive firing. We concluded that PICs broadly existed in DRN 5-HT neurons and could influence serotonergic neurotransmission in juvenile mice and that 3-week treadmill exercise induced synaptic adaptations, enhanced PICs, and thus upregulated the excitability of the 5-HT neurons.
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Affiliation(s)
- Renkai Ge
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, China.,School of Physical Education and Health Care, East China Jiaotong University, Nanchang, China
| | - Yue Dai
- Shanghai Key Laboratory of Multidimensional Information Processing, School of Communication and Electronic Engineering, East China Normal University, Shanghai, China.,Key Laboratory of Adolescent Health Assessment and Exercise Intervention of Ministry of Education, School of Physical Education and Health Care, East China Normal University, Shanghai, China
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Effects of inflammation on the developing respiratory system: Focus on hypoglossal (XII) neuron morphology, brainstem neurochemistry, and control of breathing. Respir Physiol Neurobiol 2020; 275:103389. [PMID: 31958568 DOI: 10.1016/j.resp.2020.103389] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Revised: 01/03/2020] [Accepted: 01/16/2020] [Indexed: 12/20/2022]
Abstract
Breathing is fundamental to life and any adverse change in respiratory function can endanger the health of an organism or even be fatal. Perinatal inflammation is known to adversely affect breathing in preterm babies, but lung infection/inflammation impacts all stages of life from birth to death. Little is known about the role of inflammation in respiratory control, neuronal morphology, or neural function during development. Animal models of inflammation can provide understanding and insight into respiratory development and how inflammatory processes alter developmental phenotype in addition to providing insight into new treatment modalities. In this review, we focus on recent work concerning the development of neurons, models of perinatal inflammation with an emphasis on two common LPS-based models, inflammation and its impact on development, and current and potential treatments for inflammation within the respiratory control circuitry of the mammalian brainstem. We have also discussed models of inflammation in adults and have specifically focused on hypoglossal motoneurons (XII) and neurons of the nucleus tractus solitarii (nTS) as these nuclei have been studied more extensively than other brainstem nuclei participating in breathing and airway control. Understanding the impact of inflammation on the developmental aspects of respiratory control and breathing pattern is critical to addressing problems of cardiorespiratory dysregulation in disease and this overview points out many gaps in our current knowledge.
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