Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

Coles, Jonathan A.; Poulain, Daniel

doi:10.1113/jphysiol.1991.sp018672

Cited by 48 publications

(26 citation statements)

References 55 publications

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“…The highest frequency and amplitude of bursting were observed in the mid-lactation group, at a time when the numbers of double synapses, dendritic bundling and membrane apposition would all be maximal (Theodosis et al 1981;Perlmutter, Tweedle & Hatton, 1984;Theodosis & Poulain, 1987). The increased membrane apposition occurring during lactation would be expected to enhance cell coupling, either by direct electrotonic interaction (Hatton et al 1992) or indirectly through transient spike-related increases in local potassium concentration (Coles & Poulain, 1991). Increased coupling of OT neurones during synchronous excitatory synaptic input would increase the probability of burst initiation and augment burst amplitude.…”

Section: Discussionmentioning

confidence: 99%

“…Most previous studies of OT cell bursting activity (e.g. Belin & Moos, 1986;Dyball & Leng, 1986;Coles & Poulain, 1991) have solely involved suckling as the means of evoking bursting responses. However, in the present study, in which we wished to analyse the behaviour of OT cells in different reproductive states, it seemed important to use an experimental protocol which would maximize the number of bursts we were likely to record from each OT neurone.…”

Section: Q B Jiang and J B Wakerleymentioning

confidence: 99%

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Analysis of bursting responses of oxytocin neurones in the rat in late pregnancy, lactation and after weaning.

Jiang

Wakerley

1995

The Journal of Physiology

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1. Electrophysiological recordings were undertaken to compare bursting characteristics of oxytocin (OT) neurones at four reproductive stages: day 20 pregnancy, day 22 of pregnancy (expected day of parturition), day 7‐11 of lactation, and day 5‐6 after weaning. 2. Each OT neurone was recorded for 1 h of suckling, combined with cervico‐vaginal probing at 5 min intervals as an additional stimulus for bursting. Intracerebroventricular (I.C.V.) oxytocin (2.2 ng) was given after 30 min to facilitate bursting responses. Bursts observed during suckling were classified as ‘spontaneous’ or ‘probe‐evoked’. 3. The percentage of cells displaying spontaneous and/or probe‐evoked bursts during the recording was low in day 20 pregnant animals, high in lactators and intermediate in day 20 pregnant and weaner groups. These differences may relate to variation in the proportion of animals with a responsive milk‐ejection reflex, as well as the relative size of the population of bursting OT neurones. 4. In the period before I.C.V. OT, overall burst frequency (including both spontaneous and probe‐evoked bursts) was similar across groups. After I.C.V. OT, overall burst frequency was much higher in lactators compared with other groups. Similar results were obtained when spontaneous bursts were analysed separately. 5. Burst amplitude (action potentials per burst, including both spontaneous and probe‐evoked bursts) prior to I.C.V. OT was similar between the day 20 pregnant, day 22 pregnant and lactating groups, but was lower in weaners. All groups showed an increase in burst amplitude after I.C.V. OT, but values in weaners remained lower than in other groups. In a separate analysis of spontaneous bursts, burst amplitude after I.C.V. OT was higher in lactators, and lower in weaners, than in pregnant animals. 6. Background firing rates of OT cells were higher in the day 20 and day 22 pregnant groups compared with lactators, and lower in weaners. Only OT cells in lactators showed a significant increase in background firing rates following I.C.V. OT. 7. It is concluded that the bursting characteristics of OT cells change markedly between late pregnancy, mid‐lactation and weaning. The factors underlying these changes, which are only loosely correlated with the sequence of morphological adaptations in OT cells surrounding lactation, remain to be established.

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Section: Discussionmentioning

confidence: 99%

Section: Q B Jiang and J B Wakerleymentioning

confidence: 99%

Analysis of bursting responses of oxytocin neurones in the rat in late pregnancy, lactation and after weaning.

Jiang

Wakerley

1995

The Journal of Physiology

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“…The central reference barrel was filled with Locke solution. One outer barrel was back-filled with a highly selective K + sensor based on valinomycin (Coles and Poulain, 1991), and the other with the 'ammonium' sensor. The electrode tips were beveled to an outer diameter of 3.0 to 3.5 mm on a miniature diamond grindstone (De Marco Engineering, Meyrin, CH, Switzerland).…”

Section: Measurement Of the Time Courses Of Changes In Brain Extracelmentioning

confidence: 99%

The Ammonium-Induced Increase in Rat Brain Lactate Concentration is Rapid and Reversible and is Compatible with Trafficking and Signaling Roles for Ammonium

Provent

Kickler

Barbier

et al. 2007

J Cereb Blood Flow Metab

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The glutamate-glutamine shuttle requires a flux of fixed N from neurons to astrocytes. The suggestion that some or all of this N is ammonium has received support from reports that ammonium (as NH 4 + ) rapidly enters astrocytes. Ammonium might also help control astrocyte energy metabolism by increasing lactate production. If ammonium has these functions, then its effect on brain metabolism must be rapid and reversible. To make a minimal test of this requirement, we have followed the time courses of the changes induced by a 4 min venous infusion of 1 mol/L NH 4 Cl, 2.5 mmol/kg body weight, in rat. Extracellular [NH 4 + ] in cortex, monitored with ion-selective microelectrodes, reached a peak of approximately 0.7 mmol/L 1.65 mins after the end of the infusion, then recovered. Brain metabolites were monitored non-invasively every 4 mins by 1 H magnetic resonance spectroscopy. Lactate peak area during the 3.2 min acquisition starting at the end of the infusion was 1.8460.24 times baseline (6s.e.m., P = 0.009, n = 9). Lactate increased until 13.262.1 mins after the end of the infusion and recovered halfway to baseline by 31.2 mins. Glutamate decreased by at least 7.1% (P = 0.0026). Infusion of NaCl caused no change in lactate signal. Cerebral blood flow, measured by arterial magnetization labeling, more than doubled, suggesting that the lactate increase was not caused by hypoxia. At least three consecutive ammonium-induced increases in lactate signal could be evoked. The results are compatible with an intercellular trafficking/signaling function for ammonium.

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“…These analyses have provided unequivocal evidence that glial cells contribute to the shuttling of excess K ϩ away from areas of high neuronal activity. The removal of K ϩ by glial cells is mediated by several different mechanisms (for review, see Walz, 1989;Newman, 1995), including K ϩ spatial current (Orkand et al, 1966;Dietzel et al, 1980Dietzel et al, , 1982Dietzel et al, , 1989Gardner-Medwin 1983a,b;Gardner-Medwin and Nicholson, 1983;Coles and Poulain, 1991), passive uptake of KCl (via cotransport or separate channels; Particles are found in astrocytic processes (As) in contact with the nodes of Ranvier (asterisk s) but are scarce in those membrane domains that are directly apposed to the axonal surface (arrowheads). Note the subaxolemmal electron-dense undercoating (arrows) that is characteristic of nodes.…”

Section: Activity-dependent Ion Fluxes and Osmotic Gradients In The Rmentioning

confidence: 99%

Aquaporin-4 Water Channel Protein in the Rat Retina and Optic Nerve: Polarized Expression in Müller Cells and Fibrous Astrocytes

Nagelhus¹,

Veruki

Torp³

et al. 1998

J. Neurosci.

407

358

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The water permeability of cell membranes differs by orders of magnitude, and most of this variability reflects the differential expression of aquaporin water channels. We have recently found that the CNS contains a member of the aquaporin family, aquaporin-4 (AQP4). As a prerequisite for understanding the cellular handling of water during neuronal activity, we have investigated the cellular and subcellular expression of AQP4 in the retina and optic nerve where activity-dependent ion fluxes have been studied in detail. In situ hybridization with digoxigenin-labeled riboprobes and immunogold labeling by a sensitive postembedding procedure demonstrated that AQP4 and AQP4 mRNA were restricted to glial cells, including Mü ller cells in the retina and fibrous astrocytes in the optic nerve. A quantitative immunogold analysis of the Mü ller cells showed that these cells exhibited three distinct membrane compartments with regard to AQP4 expression. End feet membranes (facing the vitreous body or blood vessels) were 10-15 times more intensely labeled than non-end feet membranes, whereas microvilli were devoid of AQP4. These data suggest that Mü ller cells play a prominent role in the water handling in the retina and that they direct osmotically driven water flux to the vitreous body and vessels rather than to the subretinal space. Fibrous astrocytes in the optic nerve similarly displayed a differential compartmentation of AQP4. The highest expression of AQP4 occurred in end feet membranes, whereas the membrane domain facing the nodal axolemma was associated with a lower level of immunoreactivity than the rest of the membrane. This arrangement may allow transcellular water redistribution to occur without inducing inappropriate volume changes in the perinodal extracellular space.

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Extracellular K+ in the supraoptic nucleus of the rat during reflex bursting activity by oxytocin neurones.

Cited by 48 publications

References 55 publications

Analysis of bursting responses of oxytocin neurones in the rat in late pregnancy, lactation and after weaning.

Analysis of bursting responses of oxytocin neurones in the rat in late pregnancy, lactation and after weaning.

The Ammonium-Induced Increase in Rat Brain Lactate Concentration is Rapid and Reversible and is Compatible with Trafficking and Signaling Roles for Ammonium

Aquaporin-4 Water Channel Protein in the Rat Retina and Optic Nerve: Polarized Expression in Müller Cells and Fibrous Astrocytes

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