NADPH-Diaphorase Positive Myenteric Neurons in the Ileum of Guinea-Pig, Rat, Rabbit and Cat: A Comparative Study

Abstract

The nitrergic system of the ileal myenteric plexus of four mammalian species was studied by means of NADPH diaphorase histochemistry which in aldehyde-fixed tissue stains only those cells that contain the constitutive, calcium-dependent nitrogen monoxide synthase isoenzyme. Since previous studies assumed minor species-specific anatomical variations, we sought similarities and differences in the nitrergic innervation pattern of the ileal musculature. In rat and guinea-pig, the ratio of nitrergic cells slightly exceeds 20%, in rabbit it is close to this number (16%), and it is lowest in cat (about 10%). The nitrergic neurons target the circular muscle layer in all investigated species where they participate in inhibitory motoric transmission. Apart from this, some elements of the sensory innervation of the circular musculature may derive from nitrergic neurons in rat and rabbit. The tertiary plexus (longitudinal muscles) is strongly supplied by NADPH diaphorase positive fibres in rat, moderately in guinea-pig and cat and not at all in rabbit. The rest of the nitrergic neurons may serve as inhibitory interneurons and control other (probably excitatory motor) neurons in the myenteric plexus. We conclude that the diverse physiological and pharmacological properties of the nitrergic system described in the small intestine in different species can be connected with the anatomical heterogeneity of its elements.

Regional differences in the number and type of myenteric neurons of the ileum of rats: a comparison of techniques of the neuronal evidentiation

“…The circular orientation of the largest axis of the ganglia of the myenteric plexus observed with the techniques employed in this work agrees with the findings in the ileum of guinea-pigs with methylene blue 1 , in the ileum of rats with NADH-d 5 , in the small intestine of guinea-pigs with cuprolinic blue 10 , and in the ileum of mice with Giemsa and ACHE 18 , but disagrees with the description of a predominately longitudinal arrangement found in the ileum of rats with NADH-d and NADPH-d 12 .…”

“…In a single species, several neuronal densities are found when the same segment of the digestive tract of animals of different ages [4][5][6] , or subjected to varied experimental conditions 7,8 , are compared. These differences are even more striking when the techniques of neuronal staining are distinct [9][10][11][12][13] . Several authors call into attention that the neuronal density can also vary in a single segment of the gut when different regions of the intestinal circumference are compared 1,4,6,11 .…”

“…Although it does not stain all the neuronal population, the histochemistry of the NADPH-d have been largely employed in the last years, because several studies indicate that the neurons which it evidences express the enzyme nitric oxide synthase (NOS) 23,24 , and thus may use nitric oxide as a neurotransmitter, being relaxation-promoting neurons, or inhibitory interneurons of the myenteric plexus 12 . The coexistence of vasoactive intestinal peptide (VIP) and NOS (evidenced by the NADPH-d) in neurons of the myenteric plexus suggests that nitric oxide (NO) and VIP can act as inhibitory, nonadrenergic noncholinergic (NANC) neurotransmitters 24,25 .…”

Gastrointestinal Function Regulation by Nitrergic Efferent Nerves

“…The presence of neurons containing NADPH diaphorase or nNOS has histologically been established in the small intestine from humans (Fang et al, 1993;Timmermans et al, 1994) and animals (Wilhelm et al, 1998;Hens et al, 2002). There is an anatomical heterogeneity of the nitrergic system in the ileum of guinea pig, rat, rabbit, and cat (Wilhelm et al, 1998).…”

“…There is an anatomical heterogeneity of the nitrergic system in the ileum of guinea pig, rat, rabbit, and cat (Wilhelm et al, 1998).…”