fg-9041 and Hypoxia

We investigated the effects of hypoxia on sharp wave-ripple complex (SPW-R) activity and recurrent epileptiform discharges in rat hippocampal slices, and the mechanisms underlying block of this activity. Oxygen levels were measured using Clark-style oxygen sensor microelectrodes. In contrast to recurrent epileptiform discharges, oxygen consumption was negligible during SPW-R activity. These network activities were reversibly blocked when oxygen levels were reduced to 20% or less for 3 min. The prolongation of hypoxic periods to 6 min caused reversible block of SPW-Rs during 20% oxygen and irreversible block when 0% oxygen (anoxia) was applied. In contrast, recurrent epileptiform discharges were more resistant to prolonged anoxia and almost fully recovered after 6 min of anoxia. SPW-Rs were unaffected by the application of 1-butyl-3-(4-methylphenylsulfonyl) urea, a blocker of KATP channels, but they were blocked by activation of adenosine A1 receptors. In support of a modulatory function of adenosine, the amplitude and incidence of SPW-Rs were increased during application of the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Interestingly, hypoxia decreased the frequency of miniature excitatory post-synaptic currents in CA3 pyramidal cells, an effect that was converted into increased frequency by the adenosine A1 agonist DPCPX. In addition, DPCPX also delayed the onset of hypoxia-mediated block of SPW-Rs. Our data suggest that early adenosine release during hypoxia induces a decrease in pre-synaptic glutamate release and that both might contribute to transient block of SPW-Rs during hypoxia/anoxia in area CA3.

Topics: Adenosine; Adenosine A1 Receptor Antagonists; Animals; Bicuculline; CA3 Region, Hippocampal; Excitatory Amino Acid Antagonists; Excitatory Postsynaptic Potentials; Female; GABA-A Receptor Antagonists; Hypoxia; In Vitro Techniques; Nerve Net; Oxygen; Patch-Clamp Techniques; Pyramidal Cells; Quinoxalines; Rats; Rats, Wistar; Valine; Xanthines

The presympathetic neurons in the rostral ventrolateral medulla (RVLM) are considered to be the source of the sympathetic activity, and there is experimental evidence that these cells present intrinsic autodepolarization. There is also evidence that an important respiratory neuronal population located in the RVLM/Bötzinger complex (BötC) corresponds to augmenting expiratory neurons (aug-E), which send projections to the phrenic nucleus in the spinal cord. However, the pacemaker activity of presympathetic neurons and the intrinsic properties of aug-E neurons had not been evaluated in brainstem slices of juvenile rats (postnatal day 35). Chronic intermittent hypoxia (CIH) is a sympathetic-mediated hypertension model, which seems to produce an associated increase in the activity of aug-E neurons. In this study, we evaluated the effects of CIH on the intrinsic properties of RVLM/BötC presympathetic and phrenic nucleus-projecting neurons (aug-E) in brainstem slices of juvenile rats (postnatal day 35). We observed that all presympathetic neurons presented spontaneous action potential firing (n = 18), which was not abolished by ionotropic receptor antagonism. In addition, exposure to 10 days of CIH produced no changes in their intrinsic passive properties, firing pattern or excitability. Most aug-E neurons presented spontaneous firing in control conditions (13 of 15 neurons), and this characteristic was preserved after blocking fast synaptic transmission (12 of 15 neurons), clearly demonstrating their intrinsic pacemaker activity. Chronic intermittent hypoxia also produced no changes in intrinsic passive properties, frequency and pattern of discharge or excitability of the aug-E neurons. The present study shows that: (i) it is possible to record the electrophysiological properties of RVLM/BötC presympathetic and aug-E neurons in brainstem slices from juvenile rats; (ii) these neurons present characteristics of intrinsic pacemakers; and (iii) their intrinsic properties were not altered by chronic intermittent hypoxia.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Animals; Bicuculline; Cervical Cord; Hypoxia; Male; Medulla Oblongata; Membrane Potentials; Neurons; Patch-Clamp Techniques; Quinoxalines; Rats, Wistar; Spinal Cord; Strychnine; Sympathetic Nervous System

Hypoxia-induced glutamate accumulation in neural tissues results in damage to neurons through excitotoxic mechanisms via activation of glutamate receptors (GluRs). Here we examine whether hypoxia in the developing retina would cause activation of the ionotropic α-amino-3-hydroxy-5-methylisoxazole-4-propioate (AMPA) GluRs and increase in Ca(2+) influx into retinal ganglion cells (RGCs) that might ultimately lead to their death. Neonatal Wistar rats were subjected to hypoxia for 2h and then sacrificed at various time points after the exposure together with normal age matched control rats. Primary cultures of RGCs were also prepared and subjected to hypoxia. Expression of AMPA glutamate receptor (GluR) 1-4 was examined in the retina. Additionally, expression of GluRs, intracellular Ca(2+) influx, reactive oxygen species (ROS) generation and cell death were investigated in cultured RGCs. GluR1-4 mRNA and protein expression showed a significant increase (P < 0.01) over control values after the hypoxic exposure both in vivo and in vitro. Cells expressing GluR1-4 in the retina were identified as RGCs by double immunofluorescence labeling with Thy1.1. Increased intracellular Ca(2+) in cultured RGCs following hypoxic exposure was reduced (P < 0.01) by 10 μM AMPA antagonist 6, 7-dinitroquinoxaline-2,3-dione (DNQX). Our results suggest that following a hypoxic insult, an increased amount of glutamate accumulates in the neonatal retina. This would then activate AMPA receptors which may damage RGCs through increased Ca(2+) accumulation and ROS generation. The involvement of AMPA receptors in damaging the RGCs is evidenced by suppression of intracellular Ca(2+) influx by DNQX which also decreased ROS generation and cell death by 50%.

Topics: Animals; Animals, Newborn; Calcium; Excitatory Amino Acid Antagonists; Hypoxia; Neuroprotective Agents; Primary Cell Culture; Quinoxalines; Rats; Rats, Wistar; Reactive Oxygen Species; Receptors, AMPA; Retinal Ganglion Cells

Magnocellular neuroendocrine cells of the supraoptic nucleus of the hypothalamus produce and release the hormones vasopressin and oxytocin in response to a variety of stimuli to regulate body water and salt as well as and parturition and lactation. The aim of the present study was to estimate oxytocin release into the blood dialysate outflowing from the vicinity of the cavernous sinus and from the femoral vein after NMDA (N-methyl-D-aspartic acid) infusion or acute hypoxia.. The samples of dialysates of venous blood outflowing from the vicinity of the cavernous sinus and, for comparison, from the femoral vein were collected in anesthetized rats. Oxytocin was determined in the sample of dialysates by radioimmunoassay.. NMDA acid infusion or acute hypoxia caused an increase of oxytocin concentration in the blood dialysate outflowing from the vicinity of the cavernous sinus of the sella turcica and from the femoral vein. A blockade of the NMDA receptors by specific and non-specific antagonists significantly inhibited the increase in the blood dialysate oxytocin concentration.. The results indicate the involvement of excitatory amino acid or acute hypoxia in the control of oxytocin release into the blood.

Topics: Animals; Cavernous Sinus; Femoral Vein; Hypoxia; Male; N-Methylaspartate; Oxytocin; Quinoxalines; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate

Electrophysiological responses to transient hypoxia were studied in neocortical brain slices from adult gerbils. Evoked responses and direct current (DC) potentials were recorded in layer III of the parietal cortex under normoxic and hypoxic conditions. The excitatory synaptic component of the evoked waveform was identified by its sensitivity to calcium and 6,7-dinitroquinoxaline-2,3-dione (DNQX). Under normoxic conditions, hypothermia reduced excitatory synaptic responses in a temperature-dependent manner. Under hypoxic conditions, hypothermia prolonged the delays to synaptic loss and hypoxic depolarization in a temperature-dependent manner. Synaptic recovery following a fixed period under hypoxic depolarization was greatly enhanced when hypoxia was administered at reduced temperature. The findings demonstrate that evoked responses are reduced under hypothermic conditions, but that these responses are sustained for a longer period of time during hypoxia. The data suggest that hypothermia protects against hypoxic damage to excitatory synaptic mechanisms in the neocortex both by prolonging the delay to hypoxic depolarization, and by extending the period of hypoxic depolarization that can be tolerated.

Topics: Animals; Calcium; Cell Hypoxia; Evoked Potentials; Gerbillinae; Hypothermia, Induced; Hypoxia; In Vitro Techniques; Parietal Lobe; Quinoxalines