Chaotic activity during iron-induced "epileptiform" discharge in rat hippocampal slices

Low-dimensional chaotic dynamics have been suggested in the rat hippocampal slice during iron-induced epileptiform activity. The dimensionality of this chaotic activity has been found to be similar in slices bathed in the same ionic extracellular medium. Some slices also displayed a drop in dimensionality prior to the onset of seizure-like activity. We suggest that techniques of nonlinear dynamical analysis are a useful reverse-engineering tool for studying the in vitro brain slice. We further conclude that neuronal circuits capable of displaying chaotic activity could exist at the level of the in vitro brain slice.

3-D computer animation of electrophysiological responses

Traditional methods for displaying electrophysiological data, that use time as the axis on a plot, are inadequate for displaying data from simultaneous multi-channel recordings. New methods proposed here plot the instantaneous value of the data on a third axis over a 2-dimensional spatial map of the tissue. The resulting 3-D computer-generated surfaces are animated over time to reveal simultaneous coherent waves of activity over the entire slice. This method was implemented for displaying multi-channel evoked potential data from rat hippocampal and human cortical slices. In rat hippocampal slice, stimulation of the Schaffer collateral-commissural pathway in stratum radiatum (SR) near CA2 elicited evoked extracellular responses along the length of CA1 from the alveus to stratum lacunosum moleculare (SLM). 3-D plotting and subsequent animation of these responses translated differential latencies of activation elicited across the slice into coherent moving patterns. These evoked waves of extracellular activity appeared to propagate along hippocampal laminae and were not readily visible in the individual plots. Human temporal cortical slices were stimulated in the white matter and evoked responses recorded in an array format. Upon plotting and animation, activity was seen to propagate vertically to the pial surface and thereafter move radially away from the stimulation site. Animation of 3-D plots of electrophysiological activity can provide instantaneous visual information on correlated changes in amplitude and latency over an entire brain slice. This means of displaying data can reduce a large number of complex wave forms to simple events and allow the simultaneous visualization of general patterns of activity in a large group of neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Spontaneous epileptiform discharges in isolated human cortical slices from epileptic patients

Human epileptic in vitro brain slices were obtained at ablative neurosurgical procedures and examined for spontaneous extracellular field potentials. Electrical events resembling interictal spikes and seizure discharges were observed in tissue from the electrocorticographic epileptic foci, but not in control tissue. It appears that important differences between the epileptic focus and normal tissue are maintained in vitro.

Dose-response testing of peptides by hippocampal brain slice recording

The brain slice chamber described offers a method of studying, with intracellular electrodes, the relationship of response to dose of peptides. By raising the level of the slices 1 mm above the level of flowing perfusion medium, we can test substances in known concentrations, free from artifacts, during long duration, stable intracellular recordings. Manipulation of Ca2+/Mg2+ ratios in the medium can help to define synaptic and second messenger mediation of the responses. The addition of substances to the perfusion medium in this system could be combined with iontophoresis and/or micropressure techniques. Pathways in the slices may also be stimulated electrically and analyzed for the involvement of various synaptic transmitters. The results with the method so far show distinct differences among the peptides studied. Thus, there are several advantages to this method in establishing the physiological role of peptides in the brain.

A constant perfusion slice chamber for stable recording during the addition of drugs

A new design for a brain slice chamber is described. This chamber has the following features: slices are maintained in a stable condition for long-term (3-4 h) intracellular recording; drugs may be injected into the flowing perfusion medium in known concentrations without disturbing intracellular penetration; a wide range of concentrations may be used to test a single cell, highly repeatable results may be obtained; only minute amounts are required of substances to be tested, and the apparatus is easy to use and clean since all parts are removable. The chamber may also be easily modified to allow for the requirements of different experiments. The chamber has been used successfully to test the effects of Ang II, carbachol, insulin and gonadotropin releasing hormone.

A biphasic excitatory response of hippocampal neurons to gonadotropin-releasing hormone

Central gonadotropin-releasing hormone (GnRH) injected intraventricularly (IVT) has been shown to facilitate rat sexual behavior. To elucidate the brain mechanisms of GnRH action, we have applied GnRH to hippocampal brain slices in vitro. Using intracellular recording from 40 hippocampal CA1 pyramidal neurons, we have found GnRH to elicit predominantly excitation. There are two types of excitatory responses. One is a short-latency, short-duration response and the second a long-latency, long-duration response. These responses were characteristic of GnRH and not peptides generally because angiotensin II, which also had an excitatory effect, had only long-latency, short-duration effects. The neural response to GnRH may be involved in the initiation of the behavioral response since the termination of the long-duration response coincides with the onset of the behavior.

Saralasin increases activity of hippocampal neurons inhibited by angiotensin II

Angiotensin II (AII) has previously been shown to specifically excite neurons in several areas of the rat brain including the hippocampus. Using a brain slice preparation for extra- and intracellular recording, we have found a small proportion of hippocampal neurons which were inhibited by AII. By applying saralasin to those pyramidal cells which are inhibited by AII, we have tested for excitatory effects of saralasin. The results showed that saralasin antagonizes AII whether its effects are inhibitory or excitatory. Saralasin alone generally decreases spontaneous activity and the results indicate that this effect may be due to an inhibition of endogenous brain angiotensin II.

Insulin inhibits pyramidal neurons in hippocampal slices

Recent studies have confirmed the presence of insulin receptors in the rat brain although their function has still not been well defined. The present study explores the possibility that insulin receptors in the brain can alter or contribute to central neurotransmission. Insulin caused a dose-dependent inhibition of hippocampal pyramidal neurons. The pattern of inhibition mirrored the binding kinetics of insulin in the hippocampus. Two related peptides, proinsulin and desoctapeptide insulin, had neuronal effects consistent with their binding to insulin receptors in the brain. Proinsulin was effective in doses 30-fold greater than insulin, whereas desoctapeptide insulin had little or no effect. These observations indicate that the inhibitory effect of insulin in this tissue may be insulin receptor-mediated and support a previously suggested functional role of insulin in the central nervous system.