Calcium Imaging and Amperometric Recording in Cultured Chromaffin Cells and Adrenal Slices from Normotensive, Wistar Kyoto Rats and Spontaneously Hypertensive Rats.

The spontaneously hypertensive rat (SHR) is a model widely used to investigate the causal mechanisms of essential hypertension. The enhanced catecholamine (CA) release reported in adrenal glands from adult SHRs raised considerable interest for its possible implication in the genesis of hypertension. The use of powerful techniques such as calcium imaging, electrophysiology, and single-cell amperometry to monitor in real time the key steps in CA secretion has allowed a better understanding of the role of chromaffin cells (CC) in the pathophysiology of hypertension, although several questions remain.

Intrinsic excitability mechanisms of neuronal ensemble formation.

Neuronal ensembles are coactive groups of cortical neurons, found in spontaneous and evoked activity, that can mediate perception and behavior. To understand the mechanisms that lead to the formation of ensembles, we co-activated layer 2/3 pyramidal neurons in brain slices from mouse visual cortex, in animals of both sexes, replicating in vitro an optogenetic protocol to generate ensembles in vivo. Using whole-cell and perforated patch-clamp pair recordings we found that, after optogenetic or electrical stimulation, coactivated neurons increased their correlated activity, a hallmark of ensemble formation.

Long-term stability of cortical ensembles.

Neuronal ensembles, coactive groups of neurons found in spontaneous and evoked cortical activity, are causally related to memories and perception, but it is still unknown how stable or flexible they are over time. We used two-photon multiplane calcium imaging to track over weeks the activity of the same pyramidal neurons in layer 2/3 of the visual cortex from awake mice and recorded their spontaneous and visually evoked responses. Less than half of the neurons remained active across any two imaging sessions.

GABA receptor: a unique modulator of excitability, Ca signaling, and catecholamine release of rat chromaffin cells.

The role of gamma-aminobutyric acid (GABA) in adrenal medulla chromaffin cell (CC) function is just beginning to unfold. GABA is stored in catecholamine (CA)-containing dense core granules and is presumably released together with CA, ATP, and opioids in response to physiological stimuli, playing an autocrine-paracrine role on CCs. The reported paradoxical "dual action" of GABA-R activation (enhancement of CA secretion and inhibition of synaptically evoked CA release) is only one aspect of GABA's multifaceted actions.

Modulation of spontaneous intracellular Ca²⁺ fluctuations and spontaneous cholinergic transmission in rat chromaffin cells in situ by endogenous GABA acting on GABAA receptors.

Using fluorescence [Ca(2+)]i imaging in rat adrenal slices, we characterized the effects of agonists and antagonists of the GABAA receptor (GABAA-R) on resting intracellular Ca(2+) ([Ca(2+)]i) and spontaneous [Ca(2+)]i fluctuations (SCFs) in hundreds of individual chromaffin cells (CCs) recorded simultaneously in situ. Muscimol, a GABAA-R agonist (20 μM; 25 s), induced an increase of resting [Ca(2+)]i in 43 ± 3 % of CCs, a decrease in 26 ± 2 %, and no response in 30 ± 5 %. In Ca(2+)-free external medium, SCFs ceased completely and muscimol failed to elicit [Ca(2+)]i rises.

Comparison of Ca2+ currents of chromaffin cells from normotensive Wistar Kyoto and spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) are widely used as model to investigate the pathophysiological mechanisms of essential hypertension. Catecholamine plasma levels are elevated in SHR, suggesting alterations of the sympathoadrenal axis. The residual hypertension in sympathectomized SHR is reduced after demedullation, suggesting a dysfunction of the adrenal medulla.