These observations support the hypotheses that ��7 nAChR may function in multiple ways and suggest that various ligands may differ in their ability to stimulate ion channel activation and/or signal transductionAlternatively, the forms of ��7-type receptors expressed in the non-neuronal cells which mediate anti-inflammatory cholinergic effects may be intrinsically different from the ion-channel forms of ��7 nAChR that are expressed in neurons. Future studies will have to be performed to elucidate the exact mechanism of action of PMP-311 and PMP-072. We hypothesize that, although PMP-072 is functionally an antagonist of ��7 nAChR AChevoked ion channel activation, it is nonetheless an agonist for ion channel-independent signal transduction. Another silent agonist, NS-6740 has been shown to reduce LPS-induced TNF release in microglia, but it was unable to improve memory retention in a cognitive mouse model. The ��7 nAChR-selective partial agonist AGN 193109 GTS-21 is also relatively ineffective at activating the ��7-receptor��s ion channel and yet has been shown to be very effective in several models for suppressing peripheral inflammation. We have shown that a factor limiting the efficacy of GTS-21 is its tendency to preferentially induce a stable desensitized state of the receptor, an effect that can be revealed with the type 2 positive allosteric modulator PNU-120596. We have hypothesized that the state in which the ion channel is desensitized may nonetheless be an active mediator of signal transduction. In this work we show that although PMP-072 is ineffective at activating ��7 nAChR-mediated ion currents, it does modulate the expression of PNU-120596-sensitive desensitization. In addition to differences in affecting ion channel activation, there were also other differential effects between PMP-311 and PMP-072. Binding studies showed that PMP-311 is quite selective and had high affinity for rat ��7 nAChR, whereas it showed lower affinity for the other nAChR tested. Functional electrophysiological experiments using human nAChR expressed in Xenopus oocytes confirmed that when PMP-311 binds to ��7 nAChR, it functions as a conventional agonist, whereas its binding to other nAChR subtypes does not produce ion channel activation. Specifically, PMP-311 acted as an antagonist of the ��4��2 nAChR. PMP-072 had a lower affinity for rat ��7 nAChR than PMP-311, but it was more selective than PMP-311 in binding to ��7 nAChR relative to ��4��2nAChR. PMP-311 showed the ability to inhibit the serotonin transporter with 72% at a concentration of 10 ��M. Inhibition of the serotonin transporter will increase serotonin availability, which could potentially lower inflammation, however levels of 10 ��Mwere not reached in the animal studies. Of note, the previously described ��Centrinone 7-selective agonist AR-R17779 also showed an anti-inflammatory effect in CIA ; the fact that AR-R17779 selectively activates ��7 nAChR without significant antagonism of ��4��2 nAChR, suggests that ��4��2 nAChR antagonist activity of PMP-311 is not required for its efficacy in treating of CIA. This notion is supported by the anti-inflammatory effect of PMP-072 described here, since it is less effective in binding to ��4��2 nAChR than PMP-311. Finally, PMP-072 exhibited markedly lower brain penetration than PMP-311. Interestingly, differences in ethnic background manifest in the intensity of melanogenesis and the morphology of dendrites, but not in the quantity of MC.