CALCIUM-DEPENDENT GLUTAMATE RELEASE DURING NEURONAL DEVELOPMENT AND SYNAPTOGENESIS - DIFFERENT INVOLVEMENT OF OMEGA-AGATOXIN IVA-SENSITIVE AND OMEGA-CONOTOXIN GVIA-SENSITIVE CHANNELS

Hippocampal neurons maintained in primary culture recycle synaptic ves icles and express functional glutamate receptors since early stages of neuronal development. By analyzing glutamate-induced cytosolic calciu m changes to sense presynaptically released neurotransmitter, we demon strate that the ability of neurons to release glutamate in the extrace llular space is temporally coincident with the property of synaptic ve sicles to undergo exocytotic-endocytotic recycling. Neuronal different iation and maturation of synaptic contacts coincide with a change in t he subtype of calcium channels primarily involved in controlling neuro secretion. Whereas omega-agatoxin IVA-sensitive channels play a role i n controlling neurotransmitter secretion at all stages of neuronal dif ferentiation, omega-conotoxin GVIA-sensitive channels are primarily in volved in mediating glutamate release at early developmental stages on ly.