Fig. 5.

P2X₇ receptors are localized presynaptically to terminal boutons in the CNS displaying characteristics of excitatory synapses and to the motor nerve terminal at the neuromuscular junction. A, A presynaptic terminal (asterisk) in the nucleus tractus solitarius of the medulla oblongata contains electron-dense DAB reaction product (dark gray). The terminal forms a synapse (arrows) of the asymmetric type with a dendritic structure (Dend). B, A presynaptic terminal (asterisk) in the intermediolateral cell column of the spinal cord forms an asymmetric type synapse (arrows) with a dendritic structure (Dend). C, At the neuromuscular junction, immunoreactivity was also located presynaptically in the motor nerve terminal (asterisk). Arrows indicate a region of synaptic specialization at the endplate. D, To determine whether P2X₇ receptor containing terminals are excitatory, a population containing purely excitatory fibers (vagal nerve afferent fibers) was anterogradely labeled before immunohistochemistry. The electron-dense DAB labeling in this case is the result of the reaction to localize the anterograde tracer, whereas the gold deposits (open arrow) indicate the presence of P2X₇ receptor immunoreactivity in these excitatory terminals. E, Another example of a DAB-labeled vagal afferent terminal that contains P2X₇ receptor immunoreactivity. F, P2X₇ receptor mRNA was detected in the nodose ganglion, the location of the neurons giving rise to central vagal afferent projections. Agarose gel electrophoresis of PCR products obtained after reverse transcription of total RNA. RT-PCR analysis revealed the presence of P2X₇ transcripts in RNA extracted from medulla (lane 1) and nodose ganglion (lane 2). No amplified products were detected when using water as template (lanes 3,6). As a positive control, the PCR products for the housekeeping gene hprt were also detected in both tissues (lanes 2, 5). Products resulting from a 1 kb molecular weight marker are indicated in lane M, and the bands correspond to the calculated size for all PCR products.