The location of penetration barriers in the ganglia of the American cockroach, Periplaneta americana (L.).

نویسندگان

  • M E Eldefrawi
  • A Toppozada
  • M M Salpeter
  • R D O'Brien
چکیده

In the period between 1950 and i960 there were a number of reports of the relative insensitivity of insect nerves and ganglia to various electrolytes, drugs and toxicants which affected vertebrate nervous systems. Examples include: potassium acting on the crural nerve of the locust, Locusta migratoria (Hoyle, 1952, 1953); potassium and acetylcholine acting on ganglia of the American cockroach Periplaneta americana (Twarog & Roeder, 1956, 1957); ionic organophosphate penetration into the nerve cord of the American cockroach (O'Brien, 1959). These findings, coupled with the finding that ionized drugs and toxicants had unexpectedly little effect on insects (O'Brien & Fisher, 1958; Kolbezen, Metcalf & Fukuto, 1954), led to the widely accepted view that insect nerves, and especially insect ganglia, were protected from cations, perhaps by the sheath or sheaths which invest most insect ganglia and nerves. Since insect ganglia are comparable to the brain and spinal cord of vertebrates, such protection would be like that offered by the so-called 'blood-brain barrier' of vertebrates. The existence of an ion-barrier was challenged when it was shown with radioactive materials that K+, Na, Ca*+ and acetylcholine enter readily the nerve cord of the American cockroach and the stick insect, Carausius morosus (Treherne, 1961 a-d, 1962, 1965; Treherne & Smith, 1965). Subsequent studies from this laboratory have explored the penetration of fatty acids, quaternary ammoniums and alcohols into ganglia of the American cockroach (Eldefrawi & O'Brien, 1966, 1967 a, b) and willow aphid (Toppozada & O'Brien, 1967) and have shown that the penetration rate of these molecules is reduced by large size and by polarity. Charged molecules do indeed penetrate more slowly than uncharged molecules of comparable size, but the difference is relatively small, in the order of 5to 15-fold. The 'barrier' is therefore relative rather than absolute. Furthermore, it is the polarity of charged molecules, rather than charge per se, which slows their penetration. In all of the above studies the location of the barrier (or 'barrier system' as Lajtha (1962) calls it in the analogous vertebrate situation) is uncertain. In principle, the external sheath might be involved, as suggested by Twarog & Roeder (1957); or there might be some more central barrier layer; or the 'barrier system' might be a non-

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عنوان ژورنال:
  • The Journal of experimental biology

دوره 48 2  شماره 

صفحات  -

تاریخ انتشار 1968