Reciprocal functional interactions between the respiration/circulation center, the upper spinal cord, and the trigeminal system

Immature functional development of lumbar locomotor networks in adult Irf8-/- mice

To date, research on the role of the brainstem and spinal cord in motor behavior has relied on in vitro preparations of the neonatal rodent spinal cord, with or without the brainstem; their spatial and temporal scope are subject to technical limitations imposed by low oxygen tension in deep tissues. Therefore, we created an arterially perfused in situ preparation that allowed us to investigate functional interactions in the CNS from the neonatal to adult period. Decerebrated rodents were kept alive via total artificial cardiopulmonary bypass for extracorporeal circulation; the plasma oxygen and ion components needed for survival were supplied through the blood vessels. Interferon regulatory factor 8 (IRF8) is a transcription factor that promotes myeloid cell development and stimulates innate immune responses. In the brain, IRF8 is expressed only in microglia and directs the expression of many genes that serve microglial functions. Recent evidence indicates that IRF8 affects behavior and modulates Alzheimer's disease progression in a mouse model. However, whether this immune deficiency arising from the absence of IRF8 influences the development of the neuronal network in the spinal cord is unknown. We applied the above methodology to mice of all ages and electrophysiologically explored whether the absence of IRF8 influences the development of lumbar central pattern generator (CPG) networks. In mice of all ages, bilateral neuronal discharges by the normal CPG networks activated by the modulated sympathetic tone via descending pathways at high flow rates became organized into discharge episodes punctuated by periods of quiescence. Similar discharge episodes were generated by the adult CPG networks (≥P14 days) activated by drug application. However, discharge episodes elicited by activating the neonatal-juvenile CPG networks ( Collapse

Key Words

• adult interferon regulatory factor 8 (IRF8)-deficient mice
• decerebrate and arterially perfused in situ preparations
• discharge episodes
• immature adult lumbar CPG
• rhythmic discharge

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Affiliation(s)

Itaru Yazawa Department of Food and Nutrition, Kyushu Nutrition Welfare University, Kitakyushu, Japan Laboratory of Neural Control, National Institute of Neurological Disorders and Stroke (NINDS), National Institutes of Health (NIH), Bethesda, MD, United States
Yuko Yoshida Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States
Ryusuke Yoshimi Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States Department of Stem Cell and Immune Regulation, Graduate School of Medicine, Yokohama City University, Yokohama, Japan
Keiko Ozato Division of Developmental Biology, National Institute of Child Health and Human Development (NICHD), NIH, Bethesda, MD, United States

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Comorbidity of cardiorespiratory and locomotor dysfunction following cervical spinal cord injury in the rat

Cervical spinal cord injury interrupts supraspinal pathways innervating thoracic sympathetic preganglionic neurons and results in cardiovascular dysfunction. Both respiratory and locomotor functions were also impaired due to damages of motoneuron pools controlling respiratory and forelimb muscles, respectively. However, no study has investigated autonomic and somatic motor functions in the same animal model. The present study aimed to establish a cervical spinal cord injury model to evaluate cardiorespiratory response and locomotor activity in unanesthetized rats. Cardiovascular response and respiratory behavior following laminectomy or cervical spinal contusion were measured using noninvasive blood pressure analyzer and plethysmography systems, respectively. Locomotor activity was evaluated by an open-field test and a locomotor rating scale. The results demonstrated that mean arterial blood pressure and heart rate were significantly reduced in contused rats compared with uninjured rats at the acute injured stage. Tidal volume was also significantly reduced during the acute and subchronic stages. Moreover, locomotor function was severely impaired, evidenced by decreasing moving ability and locomotor rating scores from the acute to chronic injured stages. Retrograde neurotracer results revealed that cervical spinal cord injury caused a reduction in number of phrenic and triceps motoneurons. Immunofluorescence staining revealed a significant attenuation of serotonergic, noradrenergic, glutamatergic, and GABAergic fibers innervating the thoracic sympathetic preganglionic neurons in chronically contused rats. These results revealed the pathological mechanism underlying the comorbidity of cardiorespiratory and locomotor dysfunction following cervical spinal cord injury. We proposed that this animal model can be used to evaluate the therapeutic efficacy of potential strategies to improve different physiological functions.NEW & NOTEWORTHY The present study establishes a preclinical rodent model to comprehensively investigate physiological functions under unanesthetized condition following cervical spinal cord contusion. The results demonstrated that cervical spinal cord contusion is associated with impairments in cardiovascular, respiratory, and locomotor function. Respiratory and forelimb motoneurons and neurochemical innervations of sympathetic preganglionic neurons were damaged following injury. This animal model can be used to evaluate the therapeutic efficacy of potential strategies to improve different physiological functions.

An aromatic substance, eugenol induces distinct depressant effects on respiratory activity in different postnatal developmental stages of the rat

Eugenol modulates neuronal activity through actions on voltage-gated ionic channels and/or transient receptor potential channels. We previously suggested that eugenol inhibited cellular (and/or network) mechanisms essential for the maintenance of the respiratory burst activity in a brainstem-spinal cord preparation from newborn rat (postnatal day 0-3). Study of the distinct effects of eugenol in neonatal and later developmental stage rats may offer new information about postnatal developmental changes of respiratory neuron networks. In the present study, therefore, we compared effects of eugenol in an in vitro newborn rat preparation with those in an arterially perfused in situ preparation from juvenile rat (postnatal day 12-15). In the former preparation, application of 1 mM eugenol decreased respiratory rate and inspiratory burst duration. In contrast, in the latter preparation, 1 mM eugenol induced a gradual decrease in the amplitude of integrated phrenic nerve activity. Phrenic nerve activity gradually recovered at 25-30 min after washout with a burst duration similar to control values. We hypothesized that the depressant effects of eugenol were caused by inhibition of cell excitability in the neonatal rat in vitro preparation but by a reduction of synaptic interactions in the juvenile rat in situ preparation.

Long-lasting facilitation of respiratory rhythm by treatment with TRPA1 agonist, cinnamaldehyde

The transient receptor potential (TRP) channels are widely distributed in the central nervous system (CNS) and peripheral nervous system. We examined the effects of TRP ankyrin 1 (TRPA1) agonists (cinnamaldehyde and allyl isothiocyanate) on respiratory rhythm generation in brainstem-spinal cord preparations from newborn rats [postnatal days 0-3 (P0-P3)] and in in situ-perfused preparations from juvenile rats (P11-P13). Preparations were superfused with modified Krebs solution at 25-26°C, and activity of inspiratory C4 ventral root (or phrenic nerve) was monitored. In the newborn rat, an in vitro preparation of cinnamaldehyde (0.5 mM) induced typically biphasic responses in C4 rate: an initial short increase and subsequent decrease, then a gradual recovery of rhythm during 15 min of bath application. After washout, the respiratory rhythm rate further increased, remaining 200% of control for >120 min, indicating long-lasting facilitation. Allyl isothiocyanate induced effects similar to those of cinnamaldehyde. The long-lasting facilitation of respiratory rhythm was partially antagonized by the TRPA1 antagonist HC-030031 (10 μM). We obtained similar long-lasting facilitation in an in situ-perfused reparation from P11-P13 rats. On the basis of results from transection experiments of the rostral medulla and whole-cell recordings from preinspiratory neurons in the parafacial respiratory group (pFRG), we suggest that the rostral medulla, including the pFRG, is important to the induction of long-lasting facilitation. A histochemical analysis demonstrated a wide distribution of TRPA1 channel-positive cells in the reticular formation of the medulla, including the pFRG. Our findings suggest that TRPA1 channel activation could induce long-lasting facilitation of respiratory rhythm and provide grounds for future study on the roles of TRPA1 channels in the CNS.