LOCALIZATION OF ALPHA-TYPE-II CALCIUM CALMODULIN-DEPENDENT PROTEIN-KINASE AT GLUTAMATERGIC BUT NOT GAMMA-AMINOBUTYRIC-ACID (GABAERGIC) SYNAPSES IN THALAMUS AND CEREBRAL-CORTEX

The alpha subunit of type II calcium/calmodulin-dependent protein kina se (CAM II kinase-alpha) plays an important role in longterm synaptic plasticity, We applied preembedding Immunocytochemistry (for CAM II ki nase-alpha) and postembedding immunogold labeling [for glutamate or ga mma-aminobutyric acid (GABA)] to explore the subcellular relationships between transmitter-defined axon terminals and the kinase at excitato ry and inhibitory synapses in thalamus and cerebral cortex. Many (but not all) axon terminals ending in asymmetric synapses contained presyn aptic CAM II kinase-alpha immunoreactivity; GABAergic terminals ending in symmetric synapses did not. Postsynaptically, CAM II kinase-alpha immunoreactivity was associated with postsynaptic densities of many (b ut not all) glutamatergic axon terminals ending on excitatory neurons. CAM LI kinase-alpha immunoreactivity was absent at postsynaptic densi ties of all GABAergic synapses. The findings shelf that CAM II kinase- alpha is selectively expressed in subpopulations of excitatory neurons and, to our knowledge, demonstrate for the first time that it is only associated with glutamatergic terminals pre- and postsynaptically. CA M II kinase-alpha is unlikely to play a role in plasticity at GABAergi c synapses.