Neurokinin-1 receptor localisation in guinea pig autonomic ganglia

We have used multiple-labelling immunohistochemistry and confocal microscop y to determine the distribution of immunoreactivity to the tachykinin neuro kinin-1 (NK1) receptors in guinea pig sympathetic ganglia. Although nerve f ibres containing immunoreactivity to substance P were common in all ganglia except the superior cervical ganglia, most neurons expressing NK1 receptor immunoreactivity were not closely surrounded by pericellular baskets of su bstance P-immunoreactive boutons. Conversely many neurons surrounded by bas kets of substance P-immunoreactive boutons lacked NK1 immunoreactivity. In the coeliac and inferior mesenteric ganglia, NK1 receptor expression was re stricted almost entirely to noradrenergic neurons that contained somatostat in immunoreactivity and projected to the enteric plexuses. In the lumbar ch ain and paracervical ganglia, NK1 immunoreactivity was expressed by nonnora drenergic vasodilator neurons containing immunoreactivity to vasoactive int estinal peptide. Taken together, our results show that sympathetic neurons in different functional pathways express NK1 receptor immunoreactivity. How ever, the neurons that could respond to endogenously released substance P t hrough NK1 receptors may be distant from presynaptic release sites. These o bservations suggest that, in sympathetic ganglia, substance P may modulate ganglionic transmission through heterosynaptic actions on NK1 receptors. J. Comp. Neurol. 412:693-704, 1999. (C) 1999 Wiley-Liss, Inc.