Maintaining network activity in submerged hippocampal slices: importance of oxygen supply

Abstract

Studies in brain slices have provided a wealth of data on the basic features of neurons and synapses. In the intact brain, these properties may be strongly influenced by ongoing network activity. Although physiologically realistic patterns of network activity have been successfully induced in brain slices maintained in interface-type recording chambers, they have been harder to obtain in submerged-type chambers, which offer significant experimental advantages, including fast exchange of pharmacological agents, visually guided patch-clamp recordings, and imaging techniques. Here, we investigated conditions for the emergence of network oscillations in submerged slices prepared from the hippocampus of rats and mice. We found that the local oxygen level is critical for generation and propagation of both spontaneously occurring sharp wave-ripple oscillations and cholinergically induced fast oscillations. We suggest three ways to improve the oxygen supply to slices under submerged conditions: (i) optimizing chamber design for laminar flow of superfusion fluid; (ii) increasing the flow rate of superfusion fluid; and (iii) superfusing both surfaces of the slice. These improvements to the recording conditions enable detailed studies of neurons under more realistic conditions of network activity, which are essential for a better understanding of neuronal network operation.

Highly Energized Inhibitory Interneurons are a Central Element for Information Processing in Cortical Networks

“…74,121 Similar observations have been made in interneuron subpopulations of the visual cortex. 124,125 We note that these findings High energy utilization 41,57,63,64,67 Exquisite sensitivity to metabolic stress 41,44,47,163,164 AP, action potential. Some unique features of (A) fast-spiking, parvalbuminpositive interneurons and (B) gamma oscillations (30 to 100 Hz) are summarized, including a selection of key references.…”

“…166 Similar findings were obtained for fast-spiking interneurons during gamma oscillations when oxygen supply was lowered. 47 This first experimental evidence suggests that even moderate hypoxia or poisoning of mitochondrial oxidative phosphorylation selectively results in rapid decrease in ATP levels and GABA release in fast-spiking interneurons. 41,167 This might be of particular importance for those fast-spiking interneurons that are located in the periphery of cortical vascular supply regions, with limited oxygen availability.…”

“…The most widespread models use acetylcholine or carbachol for activation of metabotropic cholinergic receptors, or kainate (kainic acid) for activation of ionotropic glutamatergic receptors. 40,41,46,47 Pharmacologically induced hippocampal gamma oscillations in vitro are most prominent in the neuronal network of subfield CA3, weaker in subfield CA1, and less prominent or absent in the dentate gyrus. 16,41 They can occur in the presence or in the absence of theta oscillations, 40,41 similar to the pattern of gamma oscillations in vivo.…”

Roller Coaster Scanning reveals spontaneous triggering of dendritic spikes in CA1 interneurons

“…Under these conditions, modest synaptic inputs may not be sufficient to produce dSpikes (2,3,13,14,22,23). Here we took advantage of a recently developed recording chamber with dual superfusion, in which the tissue slices could be supplied with enough oxygen to maintain physiologically relevant network activities (24) in a combination with optical detection of dSpikes (Fig. 1D).…”

Synaptic co-transmission of acetylcholine and GABA regulates hippocampal states

“…After incubation for at least 1.5 h, slices were transferred individually into a submerged-style recording chamber equipped with a single superfusion system. In case of LFP recording of hippocampal network activities, a double superfusion system was used for improved slices maintenance conditions (57,58). In the latter design, the slices were placed on a metal mesh and two separate fluid inlets allowed ACSF to flow both above and below the slices with a rate of 3-5 ml/min for each flow channel at 30-32°C (Supertech Instruments; www.super-tech.eu).…”