**4.2 Role of muscarinic receptors**

A role for mAChRs in inflammatory response is also evident. However, it appears that the direction of effect, at least in some tissues such as airway smooth muscle, is opposite to that of nicotinic receptor stimulation, in that mAChRs stimulation, leads to pro-inflammatory, rather than anti-inflammatory consequence [16]. But, in intestinal epithelial cells mAChRs play an important role in the maintenance of homeostasis. Notedly, these cells in addition to absorbing essential nutrients, also prevent the entry of foreign antigens (micro-organisms and undigested food) through mucus secretion and epithelial barrier formation. Since disruption of the intestinal epithelial homeostasis exacerbates inflammation, mAChR agonists may be of therapeutic potential in diseases associated with such disruptions such as inflammatory bowel disease [17]. However, it is important to note that unselective activation of mAChRs may have deleterious effects on intestinal epithelial barrier function. This is because subtypes of mAChRs may have distinct and in some cases opposing effects [17]. Additionally, a comprehensive understanding of the ACh network throughout the intestinal tissue, including the relationship between muscarinic and nicotinic receptors, is yet to be elucidated. In the following section, we concentrate of central interactions between these 2 distinct classes of receptors.
