Synaptic and non-synaptic AMPA receptors permeable to calcium

For a long time, alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMP A) receptors permeable to calcium have bt en considered to be either non-ex istent or as "atypical". There is now ample evidence that these receptors e xist in numerous regions of the nervous system and in many neuronal as well as non-neuronal cell populations. This evidence has been accumulated by se veral methods, including electrophysiological recording, calcium imaging an d cobalt-loading. Functional AMPA receptors permeable to calcium are alread y expressed at very early stages of embryonic development, well before the onset of synaptogenesis. They are probably involved in the paracrine signal ing necessary for construction of the nervous system before becoming involv ed in synaptic transmission. In immature cells, cyclothiazide strongly incr eases the steady-state level of responses not only to AMPA, but also to kai nate. Ingestion, during pregnancy, of food or drug substances that can cros s the placental barrier and act upon the embryonic receptors may constitute a risk for normal development. In the adult nervous system, synaptic as we ll as non-synaptic (paracrine) AMPA receptors permeable to calcium are prob ably widely expressed in both glial and neuronal cells. They may also parti cipate in controlling some aspects related to adult neurogenesis, in partic ular the migration of newly formed neurons.