Sympathetic-correlated c-Fos expression in the neonatal rat spinal cord in vitro

Modulation of synchronous sympathetic firing behaviors by endogenous GABA(A) and glycine receptor-mediated activities in the neonatal rat spinal cord in vitro

Delivering effective commands in the nervous systems require a temporal integration of neural activities such as synchronous firing. Although sympathetic nerve discharges are characterized by synchronous firing, its temporal structures and how it is modulated are largely unknown. This study used a collagenase-dissociated splanchnic sympathetic nerve-thoracic spinal cord preparation of neonatal rats in vitro as an experimental model. Several single-fiber activities were recorded simultaneously and verified by rigorous computational algorithms. Among 3763 fiber pairs that had spontaneous fiber activities, 382 fiber pairs had firing positively correlated. Their temporal relationship was quantitatively evaluated by cross-correlogram. On average, correlated firing in a fiber pair occurred in scales of ∼40ms lasting for ∼11ms. The relative frequency distribution curves of correlogram parametrical values pertinent to the temporal features were best described by trimodal Gaussians, suggesting a correlated firing originated from three or less sources. Applications of bicuculline or gabazine (noncompetitive or competitive GABA(A) receptor antagonist) and/or strychnine (noncompetitive glycine receptor antagonist) increased, decreased, or did not change individual fiber activities. Antagonist-induced enhancement and attenuation of correlated firing were demonstrated by a respective increase and decrease of the peak probability of the cross-correlograms. Heterogeneity in antagonistic responses suggests that the inhibitory neurotransmission mediated by GABA(A) and glycine receptors is not essential for but can serve as a neural substrate to modulate synchronous firing behaviors. Plausible neural mechanisms were proposed to explain the temporal structures of correlated firing between sympathetic fibers.

Downregulation of PI3Kcb utilizing adenovirus-mediated transfer of siRNA attenuates bone cancer pain

Phosphatidylinositol 3-kinase (PI3K) signaling plays a pivotal role in intracellular signal transduction pathways involved in chronic pain states. PI3K is implicated in pathomechanisms of enhanced synaptic strength, such as wind-up and central sensitization in the spinal dorsal horn. The PI3Kcb gene encoding the class 1A PI3K catalytic subunit p110beta is one of the most important molecular of the P13K signaling pathway. Here, we used small interfering RNA (siRNA) targeted to PI3Kcb by adenovirus-mediated transfer, to determine whether inhibition of PI3Kcb was a potential therapeutic target for bone cancer pain (BCP). In this study, treatment of BCP model in rats with PI3Kcb-specific siRNA resulted in inhibited pain-related behavior. Depletion of PI3Kcb decreased the protein levels of spinal PI3Kcb and phospho-Akt (P-Akt)-downstream targets of PI3K. Knockdown of PI3Kcb by siRNA also induced decreased expression of GFAP and OX42, suggesting that the upregulation of spinal PI3Kcb may increase glia excitability, at least in part by regulating glia message. Our findings suggest that siRNA-mediated gene silencing of PI3Kcb may be a useful therapeutic strategy for BCP.

Regulation of breathing and autonomic outflows by chemoreceptors

Lung ventilation fluctuates widely with behavior but arterial PCO2 remains stable. Under normal conditions, the chemoreflexes contribute to PaCO2 stability by producing small corrective cardiorespiratory adjustments mediated by lower brainstem circuits. Carotid body (CB) information reaches the respiratory pattern generator (RPG) via nucleus solitarius (NTS) glutamatergic neurons which also target rostral ventrolateral medulla (RVLM) presympathetic neurons thereby raising sympathetic nerve activity (SNA). Chemoreceptors also regulate presympathetic neurons and cardiovagal preganglionic neurons indirectly via inputs from the RPG. Secondary effects of chemoreceptors on the autonomic outflows result from changes in lung stretch afferent and baroreceptor activity. Central respiratory chemosensitivity is caused by direct effects of acid on neurons and indirect effects of CO2 via astrocytes. Central respiratory chemoreceptors are not definitively identified but the retrotrapezoid nucleus (RTN) is a particularly strong candidate. The absence of RTN likely causes severe central apneas in congenital central hypoventilation syndrome. Like other stressors, intense chemosensory stimuli produce arousal and activate circuits that are wake- or attention-promoting. Such pathways (e.g., locus coeruleus, raphe, and orexin system) modulate the chemoreflexes in a state-dependent manner and their activation by strong chemosensory stimuli intensifies these reflexes. In essential hypertension, obstructive sleep apnea and congestive heart failure, chronically elevated CB afferent activity contributes to raising SNA but breathing is unchanged or becomes periodic (severe CHF). Extreme CNS hypoxia produces a stereotyped cardiorespiratory response (gasping, increased SNA). The effects of these various pathologies on brainstem cardiorespiratory networks are discussed, special consideration being given to the interactions between central and peripheral chemoreflexes.

Chondroitinase enhances cortical map plasticity and increases functionally active sprouting axons after brain injury

The beneficial effect of interventions with chondroitinase ABC enzyme to reduce axon growth-inhibitory chondroitin sulphate side chains after central nervous system injuries has been mainly attributed to enhanced axonal sprouting. After traumatic brain injury (TBI), it is unknown whether newly sprouting axons that occur as a result of interventional strategies are able to functionally contribute to existing circuitry, and it is uncertain whether maladaptive sprouting occurs to increase the well-known risk for seizure activity after TBI. Here, we show that after a controlled cortical impact injury in rats, chondroitinase infusion into injured cortex at 30 min and 3 days reduced c-Fos⁺ cell staining resulting from the injury alone at 1 week postinjury, indicating that at baseline, abnormal spontaneous activity is likely to be reduced, not increased, with this type of intervention. c-Fos⁺ cell staining elicited by neural activity from stimulation of the affected forelimb 1 week after injury was significantly enhanced by chondroitinase, indicating a widespread effect on cortical map plasticity. Underlying this map plasticity was a larger contribution of neuronal, rather than glial cells and an absence of c-Fos⁺ cells surrounded by perineuronal nets that were normally present in stimulated naïve rats. After injury, chondroitin sulfate proteoglycan digestion produced the expected increase in growth-associated protein 43-positive axons and perikarya, of which a significantly greater number were double labeled for c-Fos after intervention with chondroitinase, compared to vehicle. These data indicate that chondroitinase produces significant gains in cortical map plasticity after TBI, and that either axonal sprouting and/or changes in perineuronal nets may underlie this effect. Chondroitinase dampens, rather than increases nonspecific c-Fos activity after brain injury, and induction of axonal sprouting is not maladaptive because greater numbers are functionally active and provide a significant contribution to forelimb circuitry after brain injury.

Glutamatergic activities in neonatal rat spinal cord heterogeneously regulate single-fiber splanchnic nerve discharge

Kynurenic acid (KYN) is a metabolite of tryptophan and is involved in various neurological disorders. Using whole-bundle nerve recording techniques, we previously observed that applications of KYN to block endogenous ionotropic glutamate receptor activities in neonatal rat spinal cords in vitro cause a reversible fluctuation of splanchnic sympathetic nerve discharge (SND). We hypothesized that the SND fluctuation was due to a heterogeneous single-fiber response. To detail individual fiber activities, we used the so-called 'oligofiber recordings'. Spontaneous single-fiber activities were recorded from the collagenase-dissociated splanchnic nerve fascicles. Applications of KYN increased, decreased or did not change firing rates. The heterogeneous responses in spontaneous spiking activities were confirmed by applications of APV or CNQX, suggesting an effect mediated by endogenous NMDA- or non-NMDA receptor activities. In addition to changes in firing rates, apparent drug-induced changes in firing patterns were also observed in some fiber activities. Using the oligofiber recording techniques, we confirmed a differential role of endogenous ionotropic glutamate receptor activities in regulating sympathetic outflows from the spinal cord of neonatal rats. Fine-tuning of ionotropic glutamate receptor activities in the spinal cord may serve as a simple way for heterogeneous regulation of various sympathetic-targeting tissues.