Morphometry and acetylcholinesterase activity of the myenteric neurons of the mouse colon in the chronic phase of experimental Trypanosoma cruzi infection.

Abstract

Abstract. The myenteric plexus of the proximal colon, midcolon, and distal colon was studied in mice chronically infected with the Y strain of Trypanosoma cruzi by means of histochemical methods for NADH-diaphorase and acetylcholinesterase (AChE) on whole mount preparations. Ganglia of infected mice displayed an irregular distribution, with neurons severely altered in form and were found side by side with slightly degenerated or morphologically normal ones. Significant reductions of at least 36% in the numbers of neurons were recorded in all regions of the colons of infected animals, especially in the distal colon where the neuron number decreased by more than 44%. Measurements of neuron size suggest that the neuronal destruction caused by T. cruzi affected the medium and large neurons. The small neurons apparently were not affected by the infection. The histochemical demonstration of AChE by the direct coloring copper ferrocyanide method showed that in the control animals, most of the neurons of the plexus displayed AChE activity in the cytoplasm although the neurons showed different reaction intensities. The AChE activity was also present, but at a lower intensity, in the myenteric plexus of the colons of infected animals. These results suggest that the T. cruzi infection affects some categories of neurons and implies that some particular enteric neurotransmitter systems could be affected and the potency of their action upon intestinal function consequently reduced.The digestive form of Chagas' disease involves denervation of the myenteric plexus, which influences disturbances of motility and absorption. 1 The extent of the neurolysis will determine the severity of the sequelae and the patient's future degree of clinical adaptation. 2 Studies involving the myenteric plexus of the colon of animals chronically infected with Trypanosoma cruzi have been carried out and have demonstrated a reduction of 34-37% of the neuronal population. 3,4 Okumura 5 found that 65% of the ganglion neurons of the mouse colon may be destroyed in experimentally infected mice. These studies were done in histologic sections made in the plane of the plexus. However, these sections rarely pass through more than a few ganglia simultaneously, while whole mount preparations, in which the muscle layers are stretched on a plane, can display the whole plexus. 6 Furthermore, the use of whole mount preparations presents the myenteric plexus as a monolayer of nerve cells, and it has therefore been possible, in parallel with neuron counts, to make measurements of neuron somata of unsectioned nerve cells. 7 Therefore, in this study, we used laminar preparations of the mouse colon to 1) quantify the loss of myenteric neurons that occurred with T. cruzi infection, 2) see whether any particular size grouping of neurons is affected, and 3) determine the activity of acetylcholinesterase (AChE) in the myenteric plexus of the mouse colon chronically infected with T. cruzi. MATERIALS AND METHODSTwenty male Swiss mice weighing 20-25 g (13-15 weeks old) were ...

Neuronal changes caused by Trypanosoma cruzi: an experimental model

“…At 75 dpi, the decrease was 52.0% IG 100 and 57.0% IG 1000 (p<0.01) compared to control. These data agree with those of other researchers (Maifrino 1996, Maifrino et al 1999 who observed neuronal decrease from 39.0% to 85.7% in the colon of mice infected with 100 and 1,000 forms of blood trypomastigotes of the strain Y, validating our findings for the establishment of a model of denervation of the chronic infection by T. cruzi in mice. Different authors showed that the colon of humans with Chagas disease presents a neuronal decrease from 55.0% to 66.67% (Adad et al 2001, Silveira et al 2007a.…”

“…A neuronal death index of 59.0% in the IG 100 and 63.4% in the IG 1000 (p<0.05) was verified when compared to the CG. It was possible to notice that such evaluation was not conducted in former studies (Maifrino 1996, Maifrino et al 1999. Statistic differences (p<0.01) were observed within the same experimental group from 18 to 75 days of infection in both IG 100 and IG 1000 .…”

“…Several studies had already showed that the destruction of the myenteric neurons triggers an important change of motility in the colon causing megacolon (Koberle 1968, 1970, Tafuri et al 1971, Maifrino et al 1999, Iantorno et al 2007, Silveira et al 2007a, b, 2008) -a phenomenon dependent on the degree of parasitism and time of infection.…”

“…The manifestations in the digestive tube occur because of the non-uniform destruction of the neuronal cells in the Enteric Nervous System -ENS (Adad et al 2001, Silveira et al 2007a. The denervation of the myenteric plexus becomes evident in the Chagas disease and it is assumed to be the major causal factor of the malfunction of the mechanisms of motility and intestinal secretion observed in the chronic phase (Maifrino et al 1999(Maifrino et al , 2005. Experimental infections indicated that neuronal denervation plays a crucial role in the changes of the gastrointestinal functions (Maifrino 1996, Maifrino et al 1999.…”

“…Experimental models are necessary for the conduction of basic research. Myenteric denervation has already been reported for murine models (Maifrino et al 1999(Maifrino et al , 2005 and can be used as an effective marker for therapeutic interventions. However, it is necessary to evaluate the occurrence of such disorders and their properties concerning the conditions of each research laboratory.…”