Histochemical localization of acetylcholinesterase in the cerebellum of some seawater teleosts

Acetylcholinesterase and butyrylcholinesterase activities in brain and plasma of freshwater teleosts: cross-species and cross-family differences

Brain and plasma acetylcholinesterase (AChE; EC 3.1.1.7) and plasma butyrylcholinesterase (BChE; EC 3.1.1.8) specific activities were assayed in 16 freshwater teleosts belonging to four families: Cyprinidae, Percidae, Esocidae and Lotidae. Brain AChE activity varied among fish species approximately 15-fold, ranging from 138 to 2011 micromol/g per h. All cyprinids had higher brain AChE activity than other fish families. Plasma AChE activity was on average 100-fold lower than that in brain, varying from 1.2 to 18.6 micromol/ml per h. Plasma BChE activity was found only in cyprinids with the exception of the common and crucian carp, and sabrefish. It varied from 26 to 1083 micromol/ml per h. In bream (Abramis brama) only 30% of specimens studied had BChE activity. The correlation coefficient values between activities of brain and plasma AChE, brain AChE and plasma BChE, plasma AChE and BChE were 0.67, 0.68 and 0.84, respectively. Cross-species and also cross-family differences in AChE and BChE activities among fish were demonstrated. Possible reasons for the differences are discussed.

The distribution of acetylcholinesterase and choline acetyl transferase in the cerebellum and posterior lateral line lobe of weakly electric fish (Gymnotidae)

Cholinesterase was demonstrated in the caudal lobe of the cerebellum but not the corpus cerebelli of weakly electric gymnotid fish. It had a patchy distribution in the granule cell layer and was very dense in the molecular layer; the cholinesterase staining was also dense in the contiguous molecular layer of the subjacent electrosensory region. Choline acetyltransferase was also found in far greater amounts within the electrosensory region and caudal lobe of the cerebellum than within the corpus cerebelli itself.

Choline acetyltransferase activity in the cerebellum and in centers of lateral line system of teleosts

Using choline acetyltransferase as a marker of cholinergic activity, different cerebellar areas and brainstem nuclei were assayed in the goldfish and the catfish. Enzyme activity resulted remarkedly higher in archicerebellum than in paleocerebellum. In addition three brainstem nuclei related to lateral line system, showed high or very high levels of choline acetyltransferase. The results suggest that cholinergic transmission would play an important role in central circuits of lateral line system, including the projection towards archicerebellar areas.

Ultastructural analysis on acetylcholinesterase localization in the cerebellar cortex of teleosts

The histochemical localization of acetylcholinesterase (AChE) was studied by electron microscopy in the cerebellar cortex of the goldfish and the catfish. The patterns of enzyme distribution show noticeable differences in the two teleost species at the level of the corresponding cerebellar structures. Among the most distinctive features is the prevailing intracellular localization of enzyme activity in the goldfish and the prevailing extracellular localization in the catfish in the molecular layer and, to a lesser extent, the granular layer. Only quantitative differences in the ability to synthesize AChE can be recorded among the different cerebellar neurons in the two species, since all these neurons exhibit different amounts of enzyme activity linked to their cytoplasmic structures. Comparing the results obtained with those of previous histochemical, experimental and developmental researches, the hypothesis seems well founded that the embryonic pool of cerebellar neurons is made up of AChE-synthesizing nruroblasts which, during development, loss or maintain to a different the mechanisms for AChE synthesis. In addition the light and electron microscope histochemistry reveals at different levels of resolution that the final pattern of AChE distribution in the cerebellar cortex is the sum of different degress of AChE synthesis by cerebellar neurons and different degrees of enzyme release in extracellular spaces.

Ultrastructural pattern of acetylcholinesterase distribution in the cerebellar cortex of the quail

The ultrastructural localization of acetylcholinesterase (AChE) was studied in the cerebellar cortex of the quail by means of histochemical method. The greater amount of AChE was detected at leve of the molecular layer in the intracellular spaces between parallel fibers and between parallel fibers and dendritic terminals. Many neurons showed intracellular localization of enzyme activity: the AChE positive neurons were all Golgi cells, most stellate the basket cells and different aliquots of Purkinje and granule cells. The enzymatic activity was usually localized in the cisternae of endoplasmic reticulum, in the nuclear envelope (but this last localization was not present in Purkinje cells- and sometimes in the Golgi apparatus; reaction granules were usually scarce in the different dendritic branches ramifying in the molecular layer. On the basis of the ultrastructural pattern of AChE distribution, some considerations are developed on the methodological aspects concerning the reliability of histochemical methods, the differences recorded at light and electron microscope level, the problems related to extracellular localization of enzyme, the difficulty of establishing a precise correlation between AChE localization in a cerebellar neuron and its possible cholinergic and/or cholinoceptive nature.

Enzymatic patterns in reptilian brain. Histochemical characterization of the optic tectum

The enzymatic patterns present in the optic tectum of 4 species belonging to different reptilian orders seem related to the degree of structural and functional organization reached by the nervous centre, as in other vertebrates. In particular the AChE localization in reptiles is representative of a evolutionary sequence in the distribution of this enzyme in the optic tectum along the tetrapode series.

Cholinesterase patterns in the cerebellum of reptiles

In the cerebellum of four species belonging to the three main reptilian orders the histochemical localization of cholinesterases has been studied. The use of different substrate-inhibitor combinations permits to record the distribution patterns of acetylcholinesterase and pseudocholinesterase, mainly revealed as butyrylcholinesterase activity. From the neurological point of view it is interesting to note that acetylcholinesterase activity shows three different distribution patterns in reptilian cerebellum, thus confirming the characteristic variability previously noticed in the cerebellar cortex of other vertebrates.

Histochemical localization of acetylcholinesterase in the cerebellum and optic tectum of four freshwater teleosts

A histochemical study has been carried out on the localization of acetylcholinesterase (AChE) in the cerebellum and optic tectum of four species of freshwater teleosts. AChE distribution in the cerebellar cortex of teleosts shows differences among the species examined and, in the trout, also differences between different cerebellar areas. This uneven kind of enzyme distribution corresponds to a similar variety of AChE patterns noticed in other vertebrates, especially mammals. AChE distribution in the optic tectum shows a prevalent pattern characterized by precise laminar distribution of enzymatic activity which is alternatively strong, weak or absent in the different tectal layers. The results suggest that most of sensitive imput and many systems of stimuli propagation may be mediated by cholinergic mechanisms in the optic tectum of telecosts.