Ileal myenteric plexus in aged guinea‐pigs: loss of structure and calretinin‐immunoreactive neurones

Abstract

Myenteric plexus controls gastrointestinal motility by means of well organized circuits which are comprised of sensory neurones, interneurones and motor neurones to the muscular layers. Calretinin (CR) is a calcium-binding protein that, in guinea-pig ileum, has only been found in ascending interneurones, which also express neurofilament triplet proteins (NFT), and excitatory longitudinal muscle motor neurones, which do not. In spite of some evidence that age affects both function and structure of the myenteric plexus, little is known about the possible selectivity of the process regarding specific myenteric neuronal phenotypes. The influence of age on both the structure of the myenteric plexus and the presence of CR-immunoreactive (CR-IR) neurones was studied using conventional immunohistochemical procedures applied to ileal whole-mount preparations from guinea-pigs. Both a reduction in ganglionic size and changes in the distribution of neurones inside and outside the ganglia, together with a general neuronal loss were found in preparations from aged guinea-pigs. More interestingly, a relatively more pronounced age-related loss of CR-IR neurones, especially those lacking of NFT expression, was found. Specific myenteric neuronal phenotypes may show differential sensitivity to ageing, and this could, under certain circumstances, alter the functional balance of gastrointestinal motility in aged individuals.

Age-related changes in the gastrointestinal tract: a functional and immunohistochemical study in guinea-pig ileum

“…In fact, in a previous work, we found several signs of structural alterations in the myenteric plexus (Abalo et al, 2005a). Thus, myenteric ganglia not only were less dense, but contained fewer neurones and were smaller in old than in young guinea pigs.…”

“…Thus, the effect of aging in the density of both the general neuronal population and of four particular immunohistochemically identified subpopulations of neurones was analysed. Packing density was the parameter chosen for this analysis because it has been shown to be relatively independent of the degree of stretching of the tissue (Karaosmanoglu et al, 1996), thus eliminating the effect of age in physical resistance to stretch, and also because most neurones are found inside the ganglia, which also occurs in aged animals (present work; Abalo et al, 2005a).…”

“…5). Finally, the presence of dots of lipofuscin-like material (Abalo et al, 2005a) was apparent in some myenteric neurones from ADULT and OLD guinea pigs (Fig. 6).…”

“…Packing density (number of neurones per ganglionic surface unit: Karaosmanoglu et al, 1996;Abalo et al, 2005a) of neurones showing immunoreactivity to CB, NOS, CR and NFT was measured on mosaics of 0.5 cm 2 consisting of 25 micrographs obtained at 20×, using the program LSM (Zeiss) for the quantitative analysis as described elsewhere (Abalo et al, 2005a). Packing density in YOUNG animals was considered as 100%, so that the age-related degrees of change of the following four populations of immunohistochemically-identified myenteric neurones (Costa et al, 1996) could be compared: sensory neurones (CB-immunoreactive), inhibitory motor neurones (NOSimmunoreactive), ascending interneurones (CR + -NFT + -neurones) and excitatory longitudinal muscle motor neurones (CR + -NFT − -neurones).…”

“…Life Sciences 80 (2007) 2436 -2445 www.elsevier.com/locate/lifescie Interestingly, the neurones primarily involved in the functionality of this tissue, the excitatory motor neurones to the longitudinal muscle, are easily identifiable by immunohistochemical methods (Costa et al, 1996). This particular population of neurones could decrease with age to a higher degree than the general population of myenteric neurones (Abalo et al, 2005a). However, the effects of ageing on the response of the LMMP preparation to excitatory or inhibitory stimuli have not yet been well established.…”