As it is well known, glutamate is one of the most widely distributed neurotransmmiters in vertebrates and invertebrates nervous systems. Glutamate neurotransmission system is involved in a wide variety of functions, including long-term potentiation and neuronal plasticity underlying memory formation. It is ascertained that different subclasses of ionotropic glutamate receptors are represented in the vertebrate brain, while in the insect CNS, up to the present, only NMDA receptors (they were cloned and sequenced, presence of protein was shown as well as pharmacology was studied), having homology to mammalian NMDA receptors and performing the similar functions, were discovered. Much less is known about kainate receptors (KR), presence of which in insect nervous system has been suggested in a few studies (Sherby, 1987; Wafford et al., 1992; Chiang et al., 2001, Lopatina et al., 2003).
The aim of the present work is to identify and to study the distribution of KR GluR 5/6/7 subunits in the brain of honeybee Apis mellifera.
The results of a western-blot analysis demonstrated that protein, which is bound specifically by antibody to GluR/5/6/7 subunits, has a molecular weight of approximately 110 kDa. Other bands have not been discovered.
Immunohistochemical staining of brain sections with the same antibody demonstrated that GluR 5/6/7 subunits are located diffusely throughout the brain. However, the most intensive signals were registered in the optic lobes, the antennal lobes and the mushroom bodies. In the optic lobes, the heterogeneous distribution of antibody staining to kainate receptors was observed. The highest levels of expression were detected in neurons of the lobula, the medulla and the lamina, while the staining of structured neuropil was much weaker. In the antennal lobes, projection and local neurons showed the most intensive signal, while in glomeruli, the GluR 5/6/7 expression was less pronounced. Mushroom bodies – high order integrative centers of the insect brain - were also characterized by irregular staining; the highest level of expression was detected in Kenyon cells.
Hence, the results of present study corroborate the hypotheses about presence in the honeybee brain of protein(s) with resemblance to mammalian kainate receptors.