The effect of experimentally induced focal epilepsy on operant responding in the rat

Quick Flicks: Association of Paroxysmal Kinesigenic Dyskinesia and Tics

Background

Paroxysmal kinesigenic dyskinesia (PKD) is a rare disorder characterised by brief attacks of chorea, dystonia, or mixed forms precipitated by sudden movement.

Methods

Observational study with a cohort of 14 PKD patients and genetic testing for PRRT2 mutations.

Results

In a series of 14 PKD patients seen in our clinic at the National Hospital of Neurology, Queen Square, from 2012–2017, we noted tics in 11 patients (79%), which stand in stark contrast to the estimated lifetime prevalence of tics estimated to reach 1%.

Conclusions

The two reasons to point out this possible association are the clinical implications and the potential opportunity of a better understanding of shared pathophysiological mechanisms of neuronal hyperexcitability.

Patterns of spontaneous activity and morphology of interneuron types in organotypic cortex and thalamus-cortex cultures

The physiological and morphological properties of interneurons in infragranular layers of rat visual cortex have been studied in organotypic cortex monocultures and thalamus-cortex co-cultures using intracellular recordings and biocytin injections. Cultures were prepared at the day of birth and maintained for up to 20 weeks. Twenty-nine interneurons of different types were characterized, in addition to 170 pyramidal neurons. The cultures developed a considerable degree of synaptically driven "spontaneous" bioelectric activity without epileptiform activity. Interneurons in cortex monocultures and thalamus-cortex co-cultures had the same physiological and morphological properties, and also pyramidal cell properties were not different in the two culture conditions. All interneurons and the majority of pyramidal cells displayed synaptically driven action potentials. The physiological group of fast-spiking interneurons included large basket cells, columnar basket cells (two cells with an arcade axon) and horizontally bitufted cells. The physiological group of slow-spiking interneurons included Martinotti cells and a "long-axon" cell. Analyses of the temporal patterns of activity revealed that fast-spiking interneurons have higher rates of spontaneous activity than slow-spiking interneurons and pyramidal cells. Furthermore, fast-spiking interneurons fired spontaneous bursts of action potentials in the gamma frequency range. We conclude from these findings that physiological and morphological properties of interneurons in organotypic mono- and co-cultures match those of interneurons characterized in vivo or in acute slice preparations, and they maintain in long-term cultures a well-balanced state of excitation and inhibition. This suggests that cortex-intrinsic or cell-autonomous mechanisms are sufficient for the expression of cell type-specific electrophysiological properties in the absence of afferents or sensory input.

Alcohol withdrawal seizures: implications of kindling

The periodic administration of convulsive agents, even at doses or intensities that initially have no convulsive effect, can lead to a progressive and enduring increase in the susceptibility to subsequent convulsive stimulation. This kindling effect has contributed to the understanding of the convulsive effects of alcohol withdrawal in three ways. First, rats kindled by the periodic application of electroconvulsive shock, local brain stimulation, or pentylenetetrazol were found to be hypersusceptible to the convulsive effects of subsequent alcohol withdrawal, thus raising the possibility that some forms of electrical or pharmacological therapy can potentiate the alcohol withdrawal syndrome in humans. Second, the duration of seizures elicited in kindled rats has been used as a sensitive index of convulsive withdrawal effects; increases in the duration of kindled motor seizures and afterdischarges can be detected following the metabolism of a single intoxicating injection of ethanol. Third, it was suggested that the potentiation of the convulsive effects of alcohol exposure and withdrawal by prior episodes of alcohol withdrawal may reflect a kindling-like process rather than an increase in physical dependence.