Central nervous tissue: an excitable medium. A study using the retinal spreading depression as a tool

Abstract

According to its physicochemical properties, neuronal tissue, including the central nervous system (CNS) and thus the human brain, is an excitable medium, which consequently exhibits, among other things, self-organization, pattern formation and propagating waves. Furthermore, such systems can be controlled by weak external forces. The spreading depression (SD), a propagating wave of excitation-depression, is such an event, which is additionally linked to a variety of medically important situations, classical migraine being just one example. Especially in retinal tissue, a true part of the CNS, the SD can be observed very easily with the naked eye and by video imaging techniques due to its big intrinsic optical signal.We have investigated the retinal SD and its control by external physical parameters such as gravity and temperature. Beyond this, especially due to its medical relevance, the control of CNS excitability by pharmacological tools is of specific interest, and we have studied this question in detail using the retinal SD as an experimental tool to collect information about the control of CNS tissue excitability.

Neuroprotective Properties of Nicotine

“…Being an excitatory drug, nicotine indeed raises the excitability of the tissue for a short introduction period, which can be seen by the spontaneous wave being elicited when nicotine is perfused. The finding, that no continuous activity is induced, as has been found with other excitatory substances like the glutamate agonist quinoline-acid [14], is most probably due to the well known fast desensitisation of AChR´s [21,22] to which nicotine by definition binds. This also results in the prolongation of the latency after longer exposition to nicotine.…”

“…As a consequence, especially in retinal tissue, a pronounced change in optical properties can be observed, the IOS concomitant with the retinal SD. Changes in parameters of this IOS induced by drugs can be used to describe the action of such substances [14].…”

Migraine With Binocular Blindness: A Clinic-Based Study

“…The investigators surmised that the repetitive blindness episodes may have reflected waves of retinal spreading depression. Work by Hanke and Fernandes de Lima 8 has shown that retinal spreading depression spreads at a rate of 4 mm per minute and its duration in vitro is about 15 minutes. It has 2 peaks or phases known as the intrinsic optical signal.…”

Primary headache disorders and neuro-ophthalmologic manifestations

“…48 Work by Hanke and de Lima has shown that retinal spreading depression spreads at a rate of 4 mm/minute and its duration in vitro is about 15 minutes. 49 Prophylactic aspirin, antiepileptic drugs, and tricyclic antidepressants have been reported to reduce the frequency of episodes of migraine with and without monocular visual defects. 47 Careful follow-up in retinal migraine patients is paramount because patients may manifest irreversible visual loss with their attacks, akin to migrainous infarction of the retina.…”