Dependence on extracellular Ca²⁺/K⁺ antagonism of inspiratory centre rhythms in slices and en bloc preparations of newborn rat brainstem

Abstract

The pre-Bötzinger Complex (preBötC) inspiratory centre remains active in isolated brainstem-spinal cords and brainstem slices. The extent to which findings in these models depend on their dimensions or superfusate [K + ] and [Ca 2+ ] (both of which determine neuronal excitability) is not clear. We report here that inspiratory-related rhythms in newborn rat slices and brainstem-spinal cords with defined boundaries were basically similar in physiological Ca 2+ (1.2 mM) and K + (3 mM). Hypoglossal nerve rhythm was 1 : 1-coupled to preBötC activity in slices and to cervical nerve bursts in en bloc preparations lacking the facial motonucleus (VII). Hypoglossal rhythm was depressed in brainstems containing (portions of) VII, while pre/postinspiratory lumbar nerve bursting was present only in preparations with > 79% VII. preBötC-related slice rhythms were inhibited in 1.5 mM Ca 2+ solution, whereas their longevity and burst rate were substantially augmented in 1 mM Ca 2+ . Ca 2+ depression of slice rhythms was antagonized by raising superfusate K + to 8-10 mM. This strong extracellular Ca 2+ /K + antagonism of inspiratory (motor) rhythms was also revealed in brainstem-spinal cords without VII, while the inhibition was progressively attenuated with increasing amount of rostral tissue. We hypothesize that depression of hypoglossal rhythm and decreased Ca 2+ sensitivity of preBötC rhythm are probably not related to an increased content of rostral respiratory structures, but rather to larger brainstem dimensions resulting in interstitial gradients for neuromodulator(s) and K + , respectively. We discuss whether block of pre/postinspiratory activity in preparations with < 79% VII is due to impairment of the pathway from preinspiratory interneurons to abdominal muscles

Connexin hemichannels contribute to spontaneous electrical activity in the human fetal cortex

“…In agreement with the current literature (36,37,54), lowering the extracellular Ca 2+ concentration from 2 mM (experimental) to 1.2 mM (physiological) significantly increased the amount of time SP neurons spent in a depolarized state (Fig. 1).…”

“…We sought an experimental approach that would increase the incidence of SP "UP states" and thus reduce the impact of silent periods. It has been previously shown that lowering Ca 2+ in the artificial cerebrospinal fluid (ACSF) improves spontaneous neuronal activity in vitro (36,37).…”

“…1 E, Left Lower), and total surface area (525.3 ± 106.3 mV·s vs. 890.1 ± 172.5 mV·s; P < 0.05; Fig. 1 Spontaneous network activity in developing circuits (37)(38)(39)(40)(41)(42)(43) generally comprises AP-mediated release of neurotransmitters and neuromodulators (44). To determine whether spontaneous electrical activity in human SP neurons at midgestation (17-23 gw) was also driven by AP-mediated release of neurotransmitters, we blocked AP initiation with bath application of tetrodotoxin (TTX; 1 μM).…”

Opioids prolong and anoxia shortens delay between onset of preinspiratory (pFRG) and inspiratory (preBötC) network bursting in newborn rat brainstems

“…However, this solution was chosen for comparison of our findings with those in a previous study on the en bloc preparation of opioid-induced changes in membrane properties of respiratory neurons [60] and imaging of optical respiratory activity in both newborn rat en bloc medullas [35] and perfused juvenile rat brainstems [43]. Besides, respiratory-related nerve and cellular activities in en bloc preparations containing the active dual respiratory center seem to be similar in both types of solutions [36,47].…”

“…The brainstem plus spinal cord was then isolated and cut rostrally between the VIth cranial nerve roots and the caudal cerebellar artery ( Fig. 1) [37,47]. After transfer to an acrylic recording chamber (volume 2 ml for whole-cell patch clamp, 1 ml for imaging), brainstem-spinal cord preparations were superfused at a flow rate of 2.5-3 ml/min (temperature 25-26°C) with solution containing (mM) 124 NaCl, 5 KCl, 1.2 KH 2 PO 4 , 2.4 CaCl 2 , 1.3 MgCl 2 , 26 NaHCO 3 , 30 D-glucose; equilibrated with 95% O 2 and 5% CO 2 , pH7.4.…”