We have used multiple-labelling immunohistochemistry and confocal microscopy to determine the distribution of immunoreactivity to the tachykinin neurokinin-1 (NK1) receptors in guinea pig sympathetic ganglia. Although nerve fibres 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 substance P-immunoreactive boutons. Conversely, many neurons surrounded by baskets of substance P-immunoreactive boutons lacked NK1 immunoreactivity. In the coeliac and inferior mesenteric ganglia, NK1 receptor expression was restricted almost entirely to noradrenergic neurons that contained somatostatin immunoreactivity and projected to the enteric plexuses. In the lumbar chain and paracervical ganglia, NK1 immunoreactivity was expressed by nonnoradrenergic vasodilator neurons containing immunoreactivity to vasoactive intestinal peptide. Taken together, our results show that sympathetic neurons in different functional pathways express NK1 receptor immunoreactivity. However, the neurons that could respond to endogenously released substance P through NK1 receptors may be distant from presynaptic release sites. These observations suggest that, in sympathetic ganglia, substance P may modulate ganglionic transmission through heterosynaptic actions on NK1 receptors.
|Number of pages||12|
|Journal||Journal of Comparative Neurology|
|Publication status||Published - 4 Oct 1999|
- Heterosynaptic transmission
- Substance P