Observation of AchE and NOS positive neurons and a comparison of Ach and NO content and Na⁺,K⁺-ATP enzyme activity of midgut and hindgut in Eriocher sinensis

The specific dynamic action in intestine is an important factor affecting transit time of food and feeding frequency,and can even influence the growth and development of decapod crustaceans.Moreover,that the midgut and hindgut of crustaceans perform different functions has also been proved.Nowadays,it is widely accepted that acetylcholinesterase(AchE)and nitric oxide synthase(NOS)positive neurons play an important role in the enteric nervous system of mammals.However,such studies in crustaceans are still rare.The aim of the present study was to clarify the distribution and morphological characteristics of AchE and NOS positive neurons throughout the E.sinensis midgut and hindgut using histochemistry,and to analyse the content of Ach and NO and Na⁺,K⁺-ATP enzyme activity of midgut and hindgut in E.sinensis by biochemical method.As far as we know,this is the first study in which whole-mount preparations of intestinal walls of midgut and hindgut in E.sinensis were respectively made and stained with H&E.The results showed that muscle layers,submucosa and basement-membrane layers were successfully obtained and observed in this study.Compared to the hindgut,the midgut muscle layer consisted of thin muscle fiber with obvious muscle fiber spacing.Submucosas of midgut and hindgut were made up of various cells.These cells were more abundant in the submucosa of hindgut than in midgut.Without obvious cell structure,basement-membrane was thin and transparent.AchE-positive neurons and NOS-positive neurons were distributed densely only in the submucosa,especially in hindgut.The AchE-positive neurons were colored brown,which ranged from 3 to 10 μm in size.The shapes of AchE-positive neurons in midgut were various,most of them were round,oval or spindle shape.The NOS-positive neurons with different sizes and shapes were colored blue.A few of these cells with cytoplasmic projections could be observed.The contents of Ach and NO and Na⁺,K⁺-ATP enzyme activity in midgut were obviously different from those in hindgut.The contents of Ach(1.28±0.41 μg/mg prot)and NO(1.84±0.25 μg/mg prot)in midgut were significantly lower than those in hindgut(Ach,1.62±0.27 μg/mg prot;NO,2.10±0.25 μg/mg prot)(P<0.05).However,Na⁺,K⁺-ATP enzyme activity of midgut(1.12±0.17 μmolPi/mg prot/h)was significantly higher than that of hindgut(0.62±0.18 μmolPi/mg prot/h)(P<0.05).In conclusion,AchE-positive neurons and NOS-positive neurons were detected mainly in the submucosa of E·sinensis intestine.There are obvious differences in the morphology of neurons and the content of neurotransmitter in midgut and hindgut of E.sinensis.