Methylxanthine-evoked perturbation of spontaneous and evoked activities in isolated newborn rat hippocampal networks.

Treatment of apnea of prematurity with methylxanthines like caffeine, aminophylline or theophylline can evoke hippocampal seizures. However, it is unknown at which interstitial brain concentrations methylxanthines promote such neonatal seizures or interfere with physiological 'early network oscillations' (ENOs) that are considered as pivotal for maturation of hippocampal neural networks. We studied theophylline and caffeine effects on ENOs in CA3 neurons (CA3-ENOs) and CA3 electrical stimulation-evoked monosynaptic CA1 field potentials (CA1-FPs) in sliced and intact hippocampi, respectively, from 8 to 10-days-old rats. Submillimolar doses of theophylline and caffeine, blocking adenosine receptors and phosphodiesterase-4 (PDE4), did not affect CA3-ENOs, ENO-associated cytosolic Ca(2+) transients or CA1-FPs nor did they provoke seizure-like discharges. Low millimolar doses of theophylline (⩾1mM) or caffeine (⩾5mM), blocking GABAA and glycine receptors plus sarcoplasmic-endoplasmic reticulum Ca(2+) ATPase (SERCA)-type Ca(2+) ATPases, evoked seizure-like discharges with no indication of cytosolic Ca(2+) dysregulation. Inhibiting PDE4 with rolipram or glycine receptors with strychnine had no effect on CA3-ENOs and did not occlude seizure-like events as tested with theophylline. GABAA receptor blockade induced seizure-like discharges and occluded theophylline-evoked seizure-like discharges in the slices, but not in the intact hippocampi. In summary, submillimolar methylxanthine concentrations do not acutely affect spontaneous CA3-ENOs or electrically evoked synaptic activities and low millimolar doses are needed to evoke seizure-like discharges in isolated developing hippocampal neural networks. We conclude that mechanisms of methylxanthine-related seizure-like discharges do not involve SERCA inhibition-related neuronal Ca(2+) dysregulation, PDE4 blockade or adenosine and glycine receptor inhibition, whereas GABA(A) receptor blockade may contribute partially.

Methylxanthines do not affect rhythmogenic preBötC inspiratory network activity but impair bursting of preBötC-driven motoneurons.

Clinical stimulation of preterm infant breathing with methylxanthines like caffeine and theophylline can evoke seizures. It is unknown whether underlying neuronal hyperexcitability involves the rhythmogenic inspiratory active pre-Bötzinger complex (preBötC) in the brainstem or preBötC-driven motor networks. Inspiratory-related preBötC interneuronal plus spinal (cervical/phrenic) or cranial hypoglossal (XII) motoneuronal bursting was studied in newborn rat en bloc brainstem-spinal cords and brainstem slices, respectively. Non-respiratory bursting perturbed inspiratory cervical nerve activity in en bloc models at >0.25mM theophylline or caffeine. Rhythm in the exposed preBötC of transected en bloc preparations was less perturbed by 10mM theophylline than cervical root bursting which was more affected than phrenic nerve activity. In the preBötC of slices, even 10mM methylxanthine did not evoke seizure-like bursting whereas >1mM masked XII rhythm via large amplitude 1-10Hz oscillations. Blocking A-type γ-aminobutyric (GABAA) receptors evoked seizure-like cervical activity whereas in slices neither XII nor preBötC rhythm was disrupted. Methylxanthines (2.5-10mM), but not blockade of adenosine receptors, phosphodiesterase-4 or the sarcoplasmatic/endoplasmatic reticulum ATPase countered inspiratory depression by muscimol-evoked GABAA receptor activation that was associated with a hyperpolarization and input resistance decrease silencing preBötC neurons in slices. The latter blockers did neither affect preBötC or cranial/spinal motor network bursting nor evoke seizure-like activity or mask corresponding methylxanthine-evoked discharges. Our findings show that methylxanthine-evoked hyperexcitability originates from motor networks, leaving preBötC activity largely unaffected, and suggest that GABAA receptors contribute to methylxanthine-evoked seizure-like perturbation of spinal motoneurons whereas non-respiratory XII motoneuron oscillations are of different origin.

Nerve growth factor acts through the TrkA receptor to protect sensory neurons from the damaging effects of the HIV-1 viral protein, Vpr.

Distal sensory polyneuropathy (DSP) with associated neuropathic pain is the most common neurological disorder affecting patients with human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS). Viral protein R (Vpr) is a neurotoxic protein encoded by HIV-1 and secreted by infected macrophages. Vpr reduces neuronal viability, increases cytosolic calcium and membrane excitability of cultured dorsal root ganglion (DRG) sensory neurons, and is associated with mechanical allodynia in vivo. A clinical trial with HIV/AIDS patients demonstrated that nerve growth factor (NGF) reduced the severity of DSP-associated neuropathic pain, a problem linked to damage to small diameter, potentially NGF-responsive fibers. Herein, the actions of NGF were investigated in our Vpr model of DSP and we demonstrated that NGF significantly protected sensory neurons from the effects of Vpr. Footpads of immunodeficient Vpr transgenic (vpr/RAG1(-/-)) mice displayed allodynia (p<0.05), diminished epidermalinnervation (p<0.01) and reduced NGF mRNA expression (p<0.001) compared to immunodeficient (wildtype/RAG1(-/-)) littermate control mice. Compartmented cultures confirmed recombinant Vpr exposure to the DRG neuronal perikarya decreased distal neurite extension (p<0.01), whereas NGF exposure at these distal axons protected the DRG neurons from the Vpr-induced effect on their cell bodies. NGF prevented Vpr-induced attenuation of the phosphorylated glycogen synthase-3 axon extension pathway and tropomyosin-related kinase A (TrkA) receptor expression in DRG neurons (p<0.05) and it directly counteracted the cytosolic calcium burst caused by Vpr exposure to DRG neurons (p<0.01). TrkA receptor agonist indicated that NGFacted through the TrkA receptor to block the Vpr-mediated decrease in axon outgrowth in neonatal and adult rat and fetal human DRG neurons (p<0.05). Similarly, inhibiting the lower affinity NGF receptor, p75, blocked Vpr's effect on DRG neurons. Overall, NGF/TrkA signaling or p75 receptor inhibition protects somatic sensory neurons exposed to Vpr, thus laying the groundwork for potential therapeutic options for HIV/AIDS patients suffering from DSP.

Activity and metabolism-related Ca2+ and mitochondrial dynamics in co-cultured human fetal cortical neurons and astrocytes.

Neurons and neighboring astrocytic glia are mostly studied in nervous tissues from rodents whereas less is known on their properties and interactions in the human brain. Here, confocal/multiphoton fluorescence imaging for several hours revealed that co-cultured fetal human cortical neurons and astrocytes show pronounced spontaneous rises of cytosolic Ca(2+) which last for up to several minutes without concomitant changes in either movements or membrane potential of mitochondria. Similar Ca(2+) rises were evoked mainly in neurons by bath-applied glutamate or γ-aminobutyric acid (GABA) acting via N-methyl-d-aspartate (NMDA)+AMPA/Kainate and GABAA receptors, respectively. Predominantly in astrocytes, Ca(2+) baseline was elevated by adenosine diphosphate (ADP) and adenosine triphosphate (ATP) acting via P2Y1 and P2X7 receptors, likely causing the release of glutamate and glutamine. Mainly astrocytes responded to histamine, whereas the activation of muscarinic acetylcholine (ACh) receptors raised Ca(2+) in both cell types. Evoked neuronal and astrocytic Ca(2+) rises could last for several minutes without affecting mitochondrial movements or membrane potential. In contrast, reversible depolarization of mitochondrial membrane potential accompanied neuronal Ca(2+) rises induced by cyanide-evoked chemical anoxia or the uncoupling of mitochondrial respiration with carbonyl-cyanide-4-(trifluoromethoxy)-phenylhydrazone (FCCP). During such metabolic perturbation, mitochondrial depolarization also occurred in astrocytes, whereas Ca(2+) was largely unaffected. In summary, fetal human cortical neurons and astrocytes show distinct patterns of neuro/glio-transmitter- and metabolically-evoked Ca(2+) rises and possess active mitochondria. One aspect of our discussion deals with the question of whether the functional mitochondria contribute to cellular Ca(2+) homeostasis that seems to be already well-developed in fetal human cortical brain cells.

Opioids prolong and anoxia shortens delay between onset of preinspiratory (pFRG) and inspiratory (preBötC) network bursting in newborn rat brainstems.

Differential responses to opioids established the hypothesis that pre/postinspiratory (Pre-I) neurons of the parafacial respiratory group (pFRG) and inspiratory (Insp) neurons of the pre-Bötzinger complex (preBötC) constitute a dual brainstem respiratory center. For further analysis of pFRG/preBötC interactions, we studied in newborn rat brainstem-spinal cord preparations opioid and anoxia effects on histologically identified pFRG-driven "type-I" Insp preBötC neurons and Pre-I neurons from three distinct respiratory brainstem regions. The micro-opioid [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO) slowed inspiratory-related cervical nerve bursts quantally, whereas anoxia induced nonquantal slowing and repetitive cervical bursts. DAMGO had no effect on membrane potential or input resistance of Pre-I neurons, while anoxia hyperpolarized them (approximately 5 mV) and decreased their resistance (approximately 30%). DAMGO prolonged the preinspiratory phase of Pre-I neuron bursting, whereas anoxia caused a shift to postinspiratory (48%) or inspiratory (22%) activity and silenced further 30% of cells. Pre-I neuron responses were not correlated with their rostrocaudal location or morphology. Neither DAMGO nor anoxia changed membrane potential of type-I neurons, but decreased their input resistance by 33% and 21%, respectively. The opposite DAMGO- and anoxia-evoked phase shifts of Pre-I neuron activity were reflected by corresponding shifts of pre/postinspiratory drive potentials in type-I neurons and, partly, by voltage-sensitive dye-imaged medullary neuronal population activities. The findings suggest that opioids presynaptically delay activation of type-I neurons as the target of drive from the pFRG to the preBötC. Contrary, anoxia seems to partly synchronize the pFRG and preBötC rhythm generators. This may enhance inspiratory and postinspiratory medullary activities for triggering multiple inspiratory motor bursts.