Immunohistochemical study on the distribution of neuron-specific enolase-and peptide-containing nerves in the reticulorumen and the reticular groove of cattle.

The distribution of nerves containing immunoreactivity for substance P (SP), vasoactive intestinal polypeptide (VIP), leucine-enkephalin (LENK), gastrin-releasing polypeptide (GRP), and somatostatin (SOM) was studied in the reticulorumen and the reticular groove of the calf and cow, use immunohistochemistry. Neuron-specific enolase (NSE) antiserum was used to determine the general distribution of nerves, which was then compared to distribution of immunoreactive (IR) nerves stained for five kinds of peptides. Nerve fibers and cell bodies were observed in all segments examined; however, both elements showed considerable variation in different segments and age groups. The densities of nerve fibers and ganglia were most concentrated in the reticular groove and least numerous in the ruminal wall. VIP-, SP-, and LENK-IR nerves were detected in all segments, whereas GRP- and SOM-IR nerves were detected only in the reticular groove. NSE-IR nerves were moderately abundant in the reticulorumen, but peptide-IR nerves composed only a minor population of nerves with VIP-IR nerves being most abundant. SP-IR nerves were less abundant and LENK-IR nerves were rarely observed. Abundant nerves were detected in the lips of the reticular groove and of these, SP-IR nerves were most abundant, and in order of decreasing abundance, VIP-, LENK-, SOM-, and GRP-IR nerves were observed also. Immunoreactive nerves were more abundant in the calf than in the cow. The reduced abundance of immunoreactive nerves in the cow as compared to calf was striking, particularly with regard to the SP-IR nerves located in the lips of the reticular groove.