Expression of P2X7 receptor immunoreactivity in distinct subsets of synaptic terminals in the ventral horn of rat lumbar spinal cord.

Adenosine 5'-triphosphate (ATP) may regulate neurotransmission in the CNS by activating presynaptic and/or postsynaptic P2X (P2X1-P2X7) ionotropic receptors. P2X7 purinergic receptors have been shown to modulate transmitter release at excitatory synapses in the hippocampus and have been localized in glutamatergic terminals in several CNS regions. Here, we analyze P2X7-immunoreactivity (IR) in a variety of immunohistochemically identified excitatory and inhibitory presynaptic terminals in the spinal cord ventral horn, including cholinergic C-terminals and motor axon collaterals and glutamatergic terminals that express VGLUT1- or VGLUT2-IR. Whereas there is widespread colocalization of P2X7-IR and VGLUT2-IR ( approximately 94%), there is little colocalization (< or =15%) with VGLUT1, monoaminergic or inhibitory terminals. Furthermore, although P2X7-IR is present in motor axon terminals at the neuromuscular junction (NMJ), only about 32% of the presumed motor axon terminals in the ventral horn exhibit P2X7-IR; in contrast, almost all large cholinergic C-terminals contacting motoneurons (91%) express P2X7-IR. The results suggest that distinct populations of synapses involved in spinal cord motor control circuits may be differentially regulated by the activation of P2X7 receptors.