Neuroscience Letters, 112 (1990) 179 183 179 Elsevier Scientific Publishers Ireland Ltd. NSL 06829 Calpain and calpastatin activity in the optic pathway Klas Blomgren and Jan-Olof Karlsson Institute of Neurobiology, University of Gothenburg, Gothenburg (Sweden) (Received 10 October 1989; Revised version received 8 December 1989; Accepted 10 January 1990) Key words: Calpain; Calpastatin; Retina; Optic nerve; Optic tract The levels of the neutral proteolytic enzymes calpains and their endogenous inhibitor calpastatin were determined in the retina and in the retrobulbar optic pathway in the albino rabbit. The highest level of calpains was observed in the optic nerve with decreasing levels in the optic tract and superior colliculus. The level of calpastatin in the retina was very low compared to that in the optic nerve and tract and other parts of the nervous system. There is indirect evidence that most neutral extra-lysosomal proteolytic activity in the mammalian brain (and other organs) is Ca-dependent [2, 5] and may, to a large extent, be due to the activity of Ca-activated proteases, calpains (EC 3.4.22.17) [4, 5]. A recent review of calpains has been published by Melloni and Pontremoli [13]. The regional distribution as well as the subcellular localization of calpains in the ner- vous system is not at all clear. It has been reported that there is, in the rat, a high calpain activity in the pons/medulla compared to the level in telencephalon [22]. The demonstration of calpains in the optic system, which can be considered a part of the CNS, has not to our knowledge been previously reported. The presence of Ca-acti- vated proteolytic systems in the optic pathway [7, 16, 19] as well as in peripheral nerves [12, 17, 20] is, however, all documented. To our knowledge there are no reports concerning the presence of the endogenous specific inhibitor to calpain, calpastatin, in central or peripheral nerves. The presence of calpastatin in CNS has been clearly shown [5, 6, 14, 15]. It has been claimed [22] that there is no variation in the regional distribution of calpastatin in the rat brain. The aim of the present investigation was to quantitate the levels of calpain and calpastatin in a few well-defined areas of the nervous system; the retina (with no or very little myelin), the optic nerve and tract (with large amounts of myelin and no neuronal cell bodies or dendrites) and the superior colliculus (closely resembling telencephalic cortex). These levels were compared to those of white matter and the temporal lobe. Correspondence: J.O. Karlsson, Institute of Neurobiology, University of Gothenburg, P.O. Box 33031, S-400 33 Gothenburg, Sweden. 0304-3940/90/$ 03.50 © 1990 Elsevier Scientific Publishers Ireland Ltd.