pH regulating transporters in neurons from various chemosensitive brainstem regions in neonatal rats.

We studied the membrane transporters that mediate intracellular pH (pH(i)) recovery from acidification in brainstem neurons from chemosensitive regions of neonatal rats. Individual neurons within brainstem slices from the retrotrapezoid nucleus (RTN), the nucleus tractus solitarii (NTS), and the locus coeruleus (LC) were studied using a pH-sensitive fluorescent dye and fluorescence imaging microscopy. The rate of pH(i) recovery from an NH(4)Cl-induced acidification was measured, and the effects of inhibitors of various pH-regulating transporters determined.

Chemosensory responses to CO2 in multiple brain stem nuclei determined using a voltage-sensitive dye in brain slices from rats.

We used epifluorescence microscopy and a voltage-sensitive dye, di-8-ANEPPS, to study changes in membrane potential during hypercapnia with or without synaptic blockade in chemosensory brain stem nuclei: the locus coeruleus (LC), the nucleus of the solitary tract, lateral paragigantocellularis nucleus, raphé pallidus, and raphé obscurus and, in putative nonchemosensitive nuclei, the gigantocellularis reticular nucleus and the spinotrigeminal nucleus. We studied the response to hypercapnia in LC cells to evaluate the performance characteristics of the voltage-sensitive dye. Hypercapnia depolarized many LC cells and the voltage responses to hypercapnia were diminished, but not eradicated, by synaptic blockade (there were intrinsically CO2-sensitive cells in the LC).

Development of chemosensitivity in neurons from the nucleus tractus solitarii (NTS) of neonatal rats.

We studied the development of chemosensitivity during the neonatal period in rat nucleus tractus solitarii (NTS) neurons. We determined the percentage of neurons activated by hypercapnia (15% CO(2)) and assessed the magnitude of the response by calculating the chemosensitivity index (CI). There were no differences in the percentage of neurons that were inhibited (9%) or activated (44.

Somatic vs. dendritic responses to hypercapnia in chemosensitive locus coeruleus neurons from neonatal rats.

Cardiorespiratory control is mediated in part by central chemosensitive neurons that respond to increased CO(2) (hypercapnia). Activation of these neurons is thought to involve hypercapnia-induced decreases in intracellular pH (pH(i)). All previous measurements of hypercapnia-induced pH(i) changes in chemosensitive neurons have been obtained from the soma, but chemosensitive signaling could be initiated in the dendrites of these neurons.

Response of membrane potential and intracellular pH to hypercapnia in neurons and astrocytes from rat retrotrapezoid nucleus.

We compared the response to hypercapnia (10%) in neurons and astrocytes among a distinct area of the retrotrapezoid nucleus (RTN), the mediocaudal RTN (mcRTN), and more intermediate and rostral RTN areas (irRTN) in medullary brain slices from neonatal rats. Hypercapnic acidosis (HA) caused pH(o) to decline from 7.45 to 7.

Oxidative stress decreases pHi and Na(+)/H(+) exchange and increases excitability of solitary complex neurons from rat brain slices.

Putative chemoreceptors in the solitary complex (SC) are sensitive to hypercapnia and oxidative stress. We tested the hypothesis that oxidative stress stimulates SC neurons by a mechanism independent of intracellular pH (pH(i)). pH(i) was measured by using ratiometric fluorescence imaging microscopy, utilizing either the pH-sensitive fluorescent dye BCECF or, during whole cell recordings, pyranine in SC neurons in brain stem slices from rat pups.