**11. Conclusions**

Several research have revealed that different bird species like chicken, pigeon and herring gulls have numerous functioning muscarinic receptors. The receptors in these species are mostly found in the central nervous system (dorsal root ganglia, basilar artery) and heart, as well as in sensory structures like the vestibular periphery and in avian salt glands respectively. Several studies have found them in the trachea, proventriculus and in smooth muscles of the intestinal tissue (ileum, rectum). The paper also reviews the existence of muscarinic receptors in quail ileum, a first report of its own in quail. Major receptor subtypes identified in avians are M2, M3, M4 and M5 except for M1 receptors present in dorsal root ganglion, atria and ventricles of heart and vestibular periphery. Even though, the muscarinic receptor subtypes in avians have been identified and characterized, the transduction mechanisms and functional contribution of each receptor subtypes has not been studied properly, which is a major shortcoming of researches in avian muscarinic receptors. For the goal of organizing the prospective neurophysiological and pharmacological research of cholinergic transmission in this species, it is crucial to establish the functional role of cholinergic systems in avians. However, in spite of the findings discussed here, rigorous studies are required in this field to further investigate the function and expression of mAChRs in avians.
