Ultrastructural localisation of substance P, vasoactive intestinal peptide and somatostatin immunoreactivities in the submucous plexus of guinea pig ileum.

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RESUMO

The submucous neurons, especially those related to the lymphatic vessels, together with their associated synapses, were studied ultrastructurally with respect to their immunoreactivities for 3 types of neuropeptides, namely substance P (SP), vasoactive intestinal peptide (VIP) and somatostatin (SOM). With the antibodies directed against the 3 types of neuropeptides, a variable number of submucous neurons including those contacting the lymphatic vessels were immunostained. Based on the immunoreactivities and synaptic relations with the submucous neurons contacting the lymphatic vessels, at least 4 types of synaptic relations with the submucous neurons contacting the lymphatic vessels, at least 4 types of synaptic configurations were observed: immunopositive terminals with positive neurons, immunopositive terminals with negative neurons, immunonegative terminals with positive neurons and immunonegative terminals with negative neurons. All 4 types of synaptic configurations were observed in SP and VIP-immunostained specimens, with the exception of type 3 which was not encountered in samples immunoreacted for SOM. When the proportions of all 4 types of peptidergic immunopositive terminals contacting the lymphatic vessel-associated neurons were totalled, the value exceeded 100%, suggesting the coexistence of 2 or more neuropeptides in the same terminals. Furthermore, some immunoreactive axon terminals made direct synaptic contacts with positive neurons suggesting the formation of the so-called 'peptide neuron chain'. It is speculated from this study that the submucous neurons receive multiple peptidergic inputs. The various synaptic contacts would imply a complicated reflex pathway in the submucous plexus.

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