Synaptic mechanisms during re-innervation of rat arterial chemoreceptors in co-culture

The carotid body plays a key role in the control of ventilation during hypo xia, a stimulus that releases catecholamines and other neurotransmitters fr om chemoreceptor (type 1) cells. Using co-cultures of rat type 1 clusters a nd 'juxtaposed' petrosal neurons (JPN), we recently showed that hypoxic che motransmission is mediated via co-release of ACh and ATP. Recordings from J PN at functional, regenerated 'synapses' in vitro revealed spontaneous acti vity consisting of random e.p.s.p.'s and/or action potentials. This activit y depended on chemical transmission since it was inhibited by extracellular solutions containing low Ca2+ /high Mg2+, or blockers of nicotinic (e.g. 1 -2 muM mecamylamine) and/or P2 purinergic (suramin or reactive blue 2; 10-5 0 muM) receptors. These solutions also inhibited hypoxia-evoked responses i n JPN. The newly formed 'synapses' appeared stable, allowing repeated demon stration of hypoxic chemotransmission in the same JPN after at least a simi lar to 24-h re-incubation period. Immunofluorescence studies in situ reveal ed positive staining of P2X2 and P2X3 purinoceptor subunits in chemoafferen t nerve terminals, but not type 1 cells; in contrast, both elements were im munopositive for the synaptic vesicle antigen (SV2). These data further sup port a co-transmitter role for ATP and the involvement of heteromeric P2X2/ P2X3 purinoceptors in carotid body function. (C) 2001 Elsevier Science Inc. All rights reserved.