title: The neurosteroid dehydroepiandrosterone (DHEA) protects the retina from AMPA-induced excitotoxicity: NGF TrkA receptor involvement.
abstract: The aim of the present study was to investigate the neuroprotective properties of the endogenous neurosteroid dehydroepiandrosterone (DHEA) in an in vivo model of retinal excitotoxicity, and the involvement of Nerve Growth Factor (NGF) in its actions. Adult Sprague-Dawley rats (250-300 g) received intravitreally (RS)-alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid hydrobromide (AMPA; 42 nmol/eye) alone or in combination with DHEA (10(-8), 10(-7), 10(-6) M), or PBS (50 mM, control group). To examine the involvement of NGF and its TrkA receptor in the pharmacological effects of DHEA, animals received AMPA and NGF (60 pg/eye) in the absence or presence of a TrkA receptor inhibitor (Calbiochem 648450, 10(-6) M) or AMPA, DHEA (10(-6) M) and TrkA receptor inhibitor (10(-6), 10(-5) M). Immunohistochemistry studies [choline acetyltransferase (ChAT), brain nitric oxide synthetase (bNOS), calbindin, and TUNEL] and fluorescence-activated cell sorting (FACS) were used to examine retinal cell loss and protection. TrkA receptor immunoreactivity (-IR) and colocalization studies with relevant markers were also performed. AMPA (42 nmol) treatment resulted in a loss of bNOS, ChAT and calbindin immunoreactivities 24 h after its administration. DHEA, administered intravitreally, protected the retina from excitotoxicity in a dose-dependent manner. This effect was mimicked by NGF, and reversed by the NGF TrkA receptor inhibitor. The TrkA receptor is expressed in ganglion cells of rat retina. TUNEL staining and FACS analysis substantiated the neuroprotective actions of DHEA. These results demonstrate for the first time that the neurosteroid DHEA, administered intravitreally, protects the retina from AMPA excitotoxicity. An NGF TrkA receptor mechanism appears to be involved in this neuroprotection.
authors.affiliation: Laboratory of Pharmacology, Department of Basic Sciences, Faculty of Medicine, University of Crete, Heraklion, Crete 71 003, Greece.
authors.forename: Despina
authors.initials: D
authors.lastname: Kokona
authors.forename: Ioannis
authors.initials: I
authors.lastname: Charalampopoulos
authors.forename: Iosif
authors.initials: I
authors.lastname: Pediaditakis
authors.forename: Achille
authors.initials: A
authors.lastname: Gravanis
authors.forename: Kyriaki
authors.initials: K
authors.lastname: Thermos
mesh_terms: D000818:Animals; D064026:Calbindins; D003687:Dehydroepiandrosterone / Q000494:pharmacology*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology*; D005260:Female; D008297:Male; D018696:Neuroprotective Agents / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D020917:Receptor, trkA / Q000378:metabolism*; D012160:Retina / Q000187:drug effects* / Q000378:metabolism; D064030:S100 Calcium Binding Protein G / Q000378:metabolism; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology*
chemical_list: D064026:Calbindins; D018690:Excitatory Amino Acid Agonists; D018696:Neuroprotective Agents; D064030:S100 Calcium Binding Protein G; D003687:Dehydroepiandrosterone; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D020917:Receptor, trkA