Chronic maternal hyperglycemia induced during mid-pregnancy in rats increases RAGE expression, augments hippocampal excitability, and alters behavior of the offspring.

Maternal diabetes during pregnancy may increase the risk of neurodevelopmental disorders in the offspring by increasing inflammation. A major source of inflammatory signaling observed in diabetes is activation of the receptor for advanced glycation end-products (RAGE), and increased RAGE expression has been reported in psychiatric disorders. Thus, we sought to examine whether maternal diabetes creates a proinflammatory state, triggered largely by RAGE signaling, that alters normal brain development and behavior of the offspring. We tested this hypothesis in rats using the streptozotocin (STZ; 50mg/kg; i.p.) model of diabetes induced during mid-pregnancy. Following STZ treatment, we observed a significant increase in RAGE protein expression in the forebrain of the offspring (postnatal day 1). Data obtained from whole-cell patch clamping of hippocampal neurons in cultures from the offspring of STZ-treated dams revealed a striking increase in excitability. When tested in a battery of behavioral tasks in early adulthood, the offspring of STZ-treated dams had significantly lower prepulse inhibition, reduced anxiety-like behavior, and altered object-place preference when compared to control offspring. In an operant-based strategy set-shifting task, STZ offspring did not differ from controls on an initial visual discrimination or reversal learning but took significantly longer to shift to a new strategy (i.e., set-shift). Insulin replacement with an implantable pellet in the dams reversed the effects of maternal diabetes on RAGE expression, hippocampal excitability, prepulse inhibition and object-place memory, but not anxiety-like behavior or set-shifting. Taken together, these results suggest that chronic maternal hyperglycemia alters normal hippocampal development and behavior of the offspring, effects that may be mediated by increased RAGE signaling in the fetal brain.

O2 sensing by recombinant TWIK-related halothane-inhibitable K+ channel-1 background K+ channels heterologously expressed in human embryonic kidney cells.

Hypoxic inhibition of K+ channels provides a link between low O2 and cell function, and in glossopharyngeal neurons hypoxic inhibition of a TWIK-related halothane-inhibitable K+ channel-1 (THIK-1)-like background K+ channel regulates neuronal function. In the present study, we examined directly the O2 sensitivity of recombinant THIK-1 channels, expressed in human embryonic kidney (HE293) cells. THIK-1 expression conferred a moderately outwardly rectifying halothane-inhibited and arachidonic acid-potentiated K+ current and invoked a strongly hyperpolarized resting membrane potential. Endogenous K+ currents in untransfected cells were unaffected by either agent. Hypoxia (P(O2), 20 mmHg) reversibly inhibited THIK-1 currents and caused membrane depolarization, effects that were occluded by halothane. Neither the mitochondrial complex I inhibitors rotenone, myxothiazol and sodium cyanide, nor the NADPH oxidase inhibitors diphenylene iodonium and phenylarsine oxide, were effective in inhibiting the O2-sensitivity of THIK-1. Thus, hypoxic inhibition of THIK-1 occurs by a mechanism dissimilar to that which regulates the activity of other members of the background K+ channel family. Given the O2 sensitivity of THIK-1 channels and their abundant expression in the CNS, we raise for the first time the possibility of a physiological and/or pathological role for these channels during brain ischemia.

Biophysical characterization of whole-cell currents in O2-sensitive neurons from the rat glossopharyngeal nerve.

In this study we use nystatin perforated-patch and conventional whole-cell recording to characterize the biophysical properties of neuronal nitric oxide synthase (nNOS)-expressing paraganglion neurons from the rat glossopharyngeal nerve (GPN), that are thought to provide NO-mediated efferent inhibition of carotid body chemoreceptors. These GPN neurons occur in two populations, a proximal one near the bifurcation of the GPN and the carotid sinus nerve, and a more distal one located further along the GPN. Both populations were visualized in whole mounts by vital staining with the styryl pyridinium dye, 4-Di-2-ASP (D289). Following isolation in vitro, proximal and distal neurons had similar input resistances (mean: 1.5 and 1.6 GOmega, respectively), input capacitances (mean: 25.0 and 27.4 pF, respectively), and resting potentials (mean: -53.9 and -53.3 mV, respectively). All neurons had similar voltage-dependent currents composed of: tetrodotoxin (TTX)-sensitive Na+ currents (IC50 approximately 0.2 microM), prolonged and transient Ca2+ currents, and delayed rectifier-type K+ currents. Threshold activation for the Na+ currents was approximately -30 mV and they were inactivated within 10 ms. Inward Ca2+ currents consisted of nifedipine-sensitive L-type, omega-agatoxin IVA-sensitive P/Q-type, omega-conotoxin GVIA-sensitive N-type, SNX-482-sensitive R-type, and Ni2+-sensitive, but SNX-482-insensitive, T-type channels. The voltage-dependent outward K+ currents were sensitive to tetraethylammonium (TEA; 10 mM) and 4-aminopyridine (4-AP; 2 mM). Exposure to a chemosensory stimulus, hypoxia (PO2 range: 80-5 Torr), caused a dose-dependent decrease in K+ current which persisted in the presence of TEA and 4-AP, consistent with the involvement of background K+ channels. Under current clamp, GPN neurons generated TTX-sensitive action potentials, and in spontaneously active neurons, hypoxia caused membrane depolarization and an increase in firing frequency. These properties endow GPN neurons with an exquisite ability to regulate carotid body chemoreceptor function during hypoxia, via voltage-gated Ca2+-entry, activation of nNOS, and release of NO.