Spinal cord injuries in humans and in other mammals are never followed by regrowth. In recent yea... more Spinal cord injuries in humans and in other mammals are never followed by regrowth. In recent years, considerable progress has been made in analyzing mechanisms that promote and inhibit regeneration. The focus of this review is changes that occur in the transition period in development when the central nervous system (CNS) changes from being able to regenerate to the adult state of failure. In our experiments we have used the neonatal opossum ( Monodelphis domestica ), which corresponds to a 14-day embryonic rat or mouse. The CNS isolated from an opossum pup and maintained in culture shows dramatic regeneration. Fibers grow through and beyond lesions and reform synaptic connections with their targets. Similarly, anesthetized neonatal pups attached to the mother recover the ability to walk after complete spinal cord transection. Although the CNS isolated from a 9-day-old animal will regenerate in vitro , CNS from a 12-day-old will not. This is the stage at which glial cells in the CNS develop. Present research is devoted toward molecular screening to determine which growth-promoting molecules decrease during development, which inhibitory molecules increase, and which receptors on growing axons become altered. Despite progress in many laboratories, major hurdles must be overcome before patients can hope to be treated. Nevertheless, the picture today is not as discouraging as it was: one can think of strategies for research on spinal cord injury so as to promote regeneration and restore function. ( Surv Ophthalmol 43 [Suppl 1] : S136-S141, 1999.
Philosophical Transactions of The Royal Society B: Biological Sciences, 2009
Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating thei... more Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating their spatial and functional relationships optically by measuring changes in intracellular calcium using the fluorescent, calcium-sensitive dye Oregon Green 488 BAPTA-1 AM while simultaneously recording the regular firing of motoneurons in the phrenic nerve in isolated brainstem/spinal cord preparations of E17 to E19 mice. Responses of identified cells are associated breath by breath with inspiratory and expiratory phases of respiration and depend on CO 2 and pH levels. Optical methods including two-photon microscopy are being developed together with computational analyses. Analysis of the spatial pattern of neuronal activity associated with respiratory rhythm, including cross-correlation analysis, reveals a network distributed in the ventral medulla with intermingling of neurons that are active during separate phases of the rhythm. Our experiments, aimed at testing whether initiation of the respiratory rhythm depends on pacemaker neurons, on networks or a combination of both, suggest an important role for networks.
ABSTRACT Optical recording of the activity of hundreds of individual neurons simultaneously withi... more ABSTRACT Optical recording of the activity of hundreds of individual neurons simultaneously within the functioning brain is now possible with calcium sensitive dyes. This offers a major advance over the limitations of single-unit recording with arrays of microelectrodes, or with functional MRI. However, the analysis of optical activity to understand neuronal interactions and circuitry underlying physiological functions requires new computational approaches. Recently it has been possible to record optically from the distributed population of neurons in the brain stem generating the respiratory rhythm, breath by breath, using the compact brain stem and spinal cord preparation of the fetal mouse stained in vitro with calcium-sensitive dye. The simultaneous electrical activity of phrenic motoneurons that innervate the diaphragm measures the timing of inspiratory breaths. In the present work, fluorescence micrographs taken at 4-100 Hz over 20-40 sec have been analyzed with the simultaneously recorded electrical signal from the phrenic nerve, in a Conditional Random Field framework. This computational analysis will be a useful tool for understanding the cellular circuitry in the living brain controlling fundamental physiological processes.
1. Martin-Caraballo M, Greer JJ: Electrophysiological properties of rat phrenic motoneurons durin... more 1. Martin-Caraballo M, Greer JJ: Electrophysiological properties of rat phrenic motoneurons during the perinatal development. J Neurophysiol 1999, 81:1365-1378 2. Greer JJ, Allan DW, Martin-Caraballo M, Lemke RP: Invited Review: An overview of phrenic nerve and diaphragm muscle development in the perinatal rat. J Appl Physiol 1999, 86:779-786 3. Martin-Caraballo M, Campagnaro PA, Gao Y, Greer JJ: Contractile properties of the rat diaphragm during the perinatal period. J Appl Physiol 2000, 88:573-580 4. Martin-Caraballo M, Greer JJ: Development of potassium conductances in perinatal rat phrenic motoneurons. J Neurophysiol 2000, 83:3497-3508 5. Martin-Caraballo M, Greer JJ: Voltage-sensitive calcium currents and their role in regulating phrenic motoneuron electrical excitability during the perinatal period. J Neurobiol 2001, 46:231-248 Acknowledgements: Funded by CIHR, AHFMR and Alberta Lung Association.
Since its introduction two decades ago, the isolated brain stem-spinal cord preparation of neonat... more Since its introduction two decades ago, the isolated brain stem-spinal cord preparation of neonatal rodents has been the preferred method used to reveal the mystery underlying the genesis of the respiratory rhythm. Little research using this in vitro approach has focused on the study of the central respiratory chemosensitivity. Some unexpected findings obtained with the brain stem-spinal cord preparation have added new questions that challenge our previous theoretic framework. Some of these findings are addressed here.
Philosophical Transactions of The Royal Society B: Biological Sciences, 2009
Nicotine may link cigarette smoking during pregnancy with sudden infant death syndrome (SIDS). Pr... more Nicotine may link cigarette smoking during pregnancy with sudden infant death syndrome (SIDS). Pre-natal nicotine leads to diminished ventilatory responses to hypercarbia and reduced central chemoreception in mice at post-natal days 0-3. We studied how pre-natal nicotine exposure changes the cholinergic contribution to central respiratory chemoreception in neonatal isolated brainstem -spinal cord and slice preparations.
Nicotine is a neuroteratogen and is the likely link between maternal cigarette smoking during pre... more Nicotine is a neuroteratogen and is the likely link between maternal cigarette smoking during pregnancy and sudden infant death syndrome (SIDS). Osmotic minipumps were implanted in 5-7 d CF1 pregnant mice to deliver nicotine bitartrate (60 mg Kg Ϫ1 day Ϫ1 ) or saline (control) solutions for up to 28 d. Prenatal to early postnatal nicotine exposure did not modify the number of newborns per litter or their postnatal growth; however, nicotine-exposed neonates hypoventilated and had reduced responses to hypercarbia (inhalation of air enriched with 10% CO 2 for 20 min) and hypoxia (inhalation of 100% N 2 for 20 s) at postnatal days 0 -3 (P0 -P3). In contrast, at postnatal day 8, nicotine-exposed neonates were indistinguishable from controls. Isolated brainstem-spinal cord preparations obtained from P0 to P3 nicotine-exposed neonates showed fictive respiration with respiratory cycles longer and more irregular than those of controls, as indicated by high short-and long-term variability in Poincaré plots. In addition, their responses to acidification were reduced, indicating compromise of central chemoreception. Furthermore, the cholinergic contribution to central chemosensory responses switched from muscarinic receptor to nicotinic receptor-based mechanisms. No significant astrogliosis was detectable in the ventral respiratory group of neurons with glial fibrillary acidic protein immunohistochemistry. These results indicate that nicotine exposure affects the respiratory rhythm pattern generator and causes a decline in central chemoreception during early postnatal life. Consequently, breathing would become highly vulnerable, failing to respond to chemosensory demands. Such impairment could be related to the ventilatory abnormalities observed in SIDS.
Spinal cord injuries in humans and in other mammals are never followed by regrowth. In recent yea... more Spinal cord injuries in humans and in other mammals are never followed by regrowth. In recent years, considerable progress has been made in analyzing mechanisms that promote and inhibit regeneration. The focus of this review is changes that occur in the transition period in development when the central nervous system (CNS) changes from being able to regenerate to the adult state of failure. In our experiments we have used the neonatal opossum ( Monodelphis domestica ), which corresponds to a 14-day embryonic rat or mouse. The CNS isolated from an opossum pup and maintained in culture shows dramatic regeneration. Fibers grow through and beyond lesions and reform synaptic connections with their targets. Similarly, anesthetized neonatal pups attached to the mother recover the ability to walk after complete spinal cord transection. Although the CNS isolated from a 9-day-old animal will regenerate in vitro , CNS from a 12-day-old will not. This is the stage at which glial cells in the CNS develop. Present research is devoted toward molecular screening to determine which growth-promoting molecules decrease during development, which inhibitory molecules increase, and which receptors on growing axons become altered. Despite progress in many laboratories, major hurdles must be overcome before patients can hope to be treated. Nevertheless, the picture today is not as discouraging as it was: one can think of strategies for research on spinal cord injury so as to promote regeneration and restore function. ( Surv Ophthalmol 43 [Suppl 1] : S136-S141, 1999.
Philosophical Transactions of The Royal Society B: Biological Sciences, 2009
Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating thei... more Respiratory rhythms arise from neurons situated in the ventral medulla. We are investigating their spatial and functional relationships optically by measuring changes in intracellular calcium using the fluorescent, calcium-sensitive dye Oregon Green 488 BAPTA-1 AM while simultaneously recording the regular firing of motoneurons in the phrenic nerve in isolated brainstem/spinal cord preparations of E17 to E19 mice. Responses of identified cells are associated breath by breath with inspiratory and expiratory phases of respiration and depend on CO 2 and pH levels. Optical methods including two-photon microscopy are being developed together with computational analyses. Analysis of the spatial pattern of neuronal activity associated with respiratory rhythm, including cross-correlation analysis, reveals a network distributed in the ventral medulla with intermingling of neurons that are active during separate phases of the rhythm. Our experiments, aimed at testing whether initiation of the respiratory rhythm depends on pacemaker neurons, on networks or a combination of both, suggest an important role for networks.
ABSTRACT Optical recording of the activity of hundreds of individual neurons simultaneously withi... more ABSTRACT Optical recording of the activity of hundreds of individual neurons simultaneously within the functioning brain is now possible with calcium sensitive dyes. This offers a major advance over the limitations of single-unit recording with arrays of microelectrodes, or with functional MRI. However, the analysis of optical activity to understand neuronal interactions and circuitry underlying physiological functions requires new computational approaches. Recently it has been possible to record optically from the distributed population of neurons in the brain stem generating the respiratory rhythm, breath by breath, using the compact brain stem and spinal cord preparation of the fetal mouse stained in vitro with calcium-sensitive dye. The simultaneous electrical activity of phrenic motoneurons that innervate the diaphragm measures the timing of inspiratory breaths. In the present work, fluorescence micrographs taken at 4-100 Hz over 20-40 sec have been analyzed with the simultaneously recorded electrical signal from the phrenic nerve, in a Conditional Random Field framework. This computational analysis will be a useful tool for understanding the cellular circuitry in the living brain controlling fundamental physiological processes.
1. Martin-Caraballo M, Greer JJ: Electrophysiological properties of rat phrenic motoneurons durin... more 1. Martin-Caraballo M, Greer JJ: Electrophysiological properties of rat phrenic motoneurons during the perinatal development. J Neurophysiol 1999, 81:1365-1378 2. Greer JJ, Allan DW, Martin-Caraballo M, Lemke RP: Invited Review: An overview of phrenic nerve and diaphragm muscle development in the perinatal rat. J Appl Physiol 1999, 86:779-786 3. Martin-Caraballo M, Campagnaro PA, Gao Y, Greer JJ: Contractile properties of the rat diaphragm during the perinatal period. J Appl Physiol 2000, 88:573-580 4. Martin-Caraballo M, Greer JJ: Development of potassium conductances in perinatal rat phrenic motoneurons. J Neurophysiol 2000, 83:3497-3508 5. Martin-Caraballo M, Greer JJ: Voltage-sensitive calcium currents and their role in regulating phrenic motoneuron electrical excitability during the perinatal period. J Neurobiol 2001, 46:231-248 Acknowledgements: Funded by CIHR, AHFMR and Alberta Lung Association.
Since its introduction two decades ago, the isolated brain stem-spinal cord preparation of neonat... more Since its introduction two decades ago, the isolated brain stem-spinal cord preparation of neonatal rodents has been the preferred method used to reveal the mystery underlying the genesis of the respiratory rhythm. Little research using this in vitro approach has focused on the study of the central respiratory chemosensitivity. Some unexpected findings obtained with the brain stem-spinal cord preparation have added new questions that challenge our previous theoretic framework. Some of these findings are addressed here.
Philosophical Transactions of The Royal Society B: Biological Sciences, 2009
Nicotine may link cigarette smoking during pregnancy with sudden infant death syndrome (SIDS). Pr... more Nicotine may link cigarette smoking during pregnancy with sudden infant death syndrome (SIDS). Pre-natal nicotine leads to diminished ventilatory responses to hypercarbia and reduced central chemoreception in mice at post-natal days 0-3. We studied how pre-natal nicotine exposure changes the cholinergic contribution to central respiratory chemoreception in neonatal isolated brainstem -spinal cord and slice preparations.
Nicotine is a neuroteratogen and is the likely link between maternal cigarette smoking during pre... more Nicotine is a neuroteratogen and is the likely link between maternal cigarette smoking during pregnancy and sudden infant death syndrome (SIDS). Osmotic minipumps were implanted in 5-7 d CF1 pregnant mice to deliver nicotine bitartrate (60 mg Kg Ϫ1 day Ϫ1 ) or saline (control) solutions for up to 28 d. Prenatal to early postnatal nicotine exposure did not modify the number of newborns per litter or their postnatal growth; however, nicotine-exposed neonates hypoventilated and had reduced responses to hypercarbia (inhalation of air enriched with 10% CO 2 for 20 min) and hypoxia (inhalation of 100% N 2 for 20 s) at postnatal days 0 -3 (P0 -P3). In contrast, at postnatal day 8, nicotine-exposed neonates were indistinguishable from controls. Isolated brainstem-spinal cord preparations obtained from P0 to P3 nicotine-exposed neonates showed fictive respiration with respiratory cycles longer and more irregular than those of controls, as indicated by high short-and long-term variability in Poincaré plots. In addition, their responses to acidification were reduced, indicating compromise of central chemoreception. Furthermore, the cholinergic contribution to central chemosensory responses switched from muscarinic receptor to nicotinic receptor-based mechanisms. No significant astrogliosis was detectable in the ventral respiratory group of neurons with glial fibrillary acidic protein immunohistochemistry. These results indicate that nicotine exposure affects the respiratory rhythm pattern generator and causes a decline in central chemoreception during early postnatal life. Consequently, breathing would become highly vulnerable, failing to respond to chemosensory demands. Such impairment could be related to the ventilatory abnormalities observed in SIDS.
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Papers by Jaime Eugenin