Neurophysiology

The primary goal of our neurophysiological studies is to understand the mechanisms by which inhibitory and excitatory neurons generate pathological activity, such as in vitro seizures. We perform simultaneous dual/triple whole-cell and extracellular recordings from the identified neuronal subtypes in the CA1 area of the rodent hippocampal and neocortical slices. We visualize living cells using infrared contrast microscopy.

Neuronal subtype identification based on electrophysiology and immunohistochemistry.

Neuronal cell subtypes can be distinguished based on their soma location and appearance, active membrane properties, cell-specific markers, and axonal arborizations. Below are examples of the active membrane properties in neocortical interneuron (left) and pyramidal cell (right) following an incrementally increasing 400msec positive current pulses (recorded in the rodent visual cortex layers II-III).

Post-hoc cell subtype identification

During the recordings, cells are filled with an intracellular stain - neurobiotin (NB). Post-hoc, the recorded cells are cross stained for cell subtype specific markers (like somatostatin, SOM or parvalbumin, PV; below on the left) and streptavidin antibody is used to recover the detailed dendro-axonic morphology (photomicrograph and reconstruction on the right).

In vitro interictal bursts and seizures.

The most common seizure model that we use employs blockade of potassium channels by the 4-Aminopyridine (4-AP) in the lowered extracellular magnesium (0.6mM) artificial cerebrospinal fluid (ACSF). In the presence of 4-AP, hippocampal neurons generate complex spontaneous events like shorter duration (1-500msec) interictal bursts (A-C) and long duration (30-60sec) massive seizures.

Interneuron-Pyramidal cell interplay during in vitro seizures.

After numerous recordings from distinct cellular subtype pairs in the CA1 area of the hippocampus, we show that seizures cannot be explained as a straight forward increae in synchrony in all cells at once and that they are indeed orchestrated by a complex cell-specific activation patterns (Ziburkus et al., 2006). Below are three examples of spiking interactions between pyramidal-pyramidal, OLM interneuron-pyramidal, and OLM-OLM cell pairs before during and after the ictal-like events.

Cartoon and pictures illustrating simultaneous multielectrode recording technique in the hippocampal and neocortical slices.