Modulatory Effects of Dopamine D2 Receptors on Spreading Depression in Rat Somatosensory Neocortex

INTRODUCTION

Spreading depression (SD) is a propagating wave of depolarization followed by depression of the neuroglial activities and can modulate extracellular dopamine concentrations in the neocortex. It has been shown that the dopaminergic system plays a role in migraine. SD has been suggested as a critical phenomenon in the pathophysiology of migraine. The aim of this study was to investigate the effect of dopamine D2 receptors on the characteristic features of SD in rat neocortical tissues.

METHODS

The effect of dopamine D2 receptor agonist quinpirole and D2 receptor antagonist sulpiride was tested on different characteristic features (amplitude, duration and velocity) of KCl-induced SD in somatosensory neocortical slices of adult rats. The effect of above-mentioned substances on production of long-term potentiation (LTP) in the neocortex was also evaluated.

RESULTS

The present data revealed a dose-dependent suppression of the amplitude and duration of SD in the presence of the dopamine D2 receptor antagonist sulpiride in the neocortex. D2 dopamine receptor agonist quinpirole dose-dependently enhanced the amplitude and duration of the neocortical SD. Furthermore, application of D2 receptor antagonist significantly suppressed induction of LTP.

DISCUSSION

These results indicate that D2 receptors modulate the initiation of SD in the neocortex. This finding refers to the potential role of D2 receptor antagonist in treatment of migraine pain.

Spreading depolarization in the ischemic brain: does aging have an impact?

Recurrent waves of spreading depolarization (SD) spontaneously occur minutes after the onset of focal ischemia in the brain and keep generating for a number of days to follow. It has become widely accepted that ischemia-related SDs are part of the pathophysiology of cerebrovascular diseases and predict worse outcome. SDs may exacerbate ischemic injury via related atypical hemodynamic responses. The incidence of ischemic stroke is known to increase markedly with age; yet, very few studies investigated whether age alters SD evolution and whether a potential age-specific pattern of SD would contribute to the age-related intensification of infarct development. Experimental data demonstrate that aging has a marked impact on SD evolution and corresponding changes in cerebral blood flow. We hypothesize that an age-specific pattern of the SD-associated hemodynamic response must be involved in augmenting the expansion of ischemic brain damage in the elderly patients and that structural and functional (mal)adaptation of the cerebrovascular system with aging serves as a potential basis for compromised vascular reactivity and subsequent tissue damage. The concept put forward is expected to stimulate further investigation to achieve a comprehensive overview of the implication of SD in injury progression in the aged brain.

Familial hemiplegic migraine and spreading depression

Familial hemiplegic migraine (FHM) is an autosomal dominantly inherited subtype of migraine with aura, characterized by transient neurological signs and symptoms. Typical hemiplegic migraine attacks start in the first or second decade of life. Some patients with FHM suffer from daily recurrent attacks since childhood. Results from extensive studies of cellular and animal models have indicated that gene mutations in FHM increase neuronal excitability and reduce the threshold for spreading depression (SD). SD is a transient wave of profound neuronal and glial depolarization that slowly propagates throughout the brain tissue and is characterized by a high amplitude negative DC shift. After induction of SD, S218L mutant mice exhibited neurological signs highly reminiscent of clinical attacks in FHM type 1 patients carrying this mutation. FHM1 with ataxia is attributable to specific mutations that differ from mutations that cause pure FHM1 and have peculiar consequences on cerebellar Cav2.1 currents that lead to profound Purkinje cell dysfunction and neuronal loss with atrophy. SD in juvenile rats produced neuronal injury and death. Hormonal factors involved in FHM affect SD initiation and propagation. The data identify SD as a possible target of treatment of FHM. In addition, FHM is a useful model to explore the mechanisms of more common types of migraine.