5 -nucleotidase cerebellum

Steady state concentrations of adenosine are maintained through the activities of only three enzymes, 5 -nucleotidase (5 -N), adenosine kinase and adenosine deaminase. Adenosine kinase and adenosine deaminase were located mainly in the soluble fractions of rat cerebellar homogenates, whereas 5 -N was present in subcellular fractions (Philips and Newsholme, 1979), mainly in the synaptosomal fraction (Marani, 1977). Adenosine deaminase-immunoreactivity in rat cerebellum was present with one out of five polyclonal sera prepared by Nagy et ah (1988). Staining was present in most Purkinje cells with a variation in intensity. Staining was observed in the Purkinje cell axons and terminals in the cerebellar and vestibular nuclei. The localization of 5 -N will be discussed below. 

Nucleotidase (5 -N) is an integral glycoprotein of the cellular plasma membrane in a wide range of animal cells. Its functional role is still unclear. Possibilities. include recovery of purines and pyrimidines from the extracellular space, the extracellular formation of neuromodular adenosine from released nucleotidases and non-enzymatic functions related to the interaction of 5 -nucleotidase with compartments of the cytoskel-eton and extracellular matrix (Schoen et al., 1987). 5 -N catalyses the production of adenosine by the hydrolytic cleavage of 5 -nucleotide monophosphates (i.e. adenosine-5 -monophosphate). The development of 5 -N in the cerebellum was studied by Schoen et al. (1987, 1988, 1990). 

Fig. 59. 5 -Nucleotidase immunohistochemical staining of rat cerebellum. A. Immunofluorescence. B. PAP-method. Enzyme activity is predominantly found within the molecular layer on Bergmann glial fibers (long arrows). Purkinje cells are surrounded by fine rims of reaction product (small arrows). Within the granular layer 5 -nucleotidase activity is diffusely scattered between granule cells (arrow heads). Vibratome sections. C. Longitudinally sectioned Bergmann glia cell processes (B) of the molecular layer of rat cerebellum. Fine DAB reaction product is located on adjacent membranes of these processes (arrows). Bars in A,B = 50 /tm, in C = 0.5 nm. Schoen et al. (1987).

Fig. 131. Reconstructions of the zonal distribution of 5 -nucleotidase (5 -N) in the molecular layer of the cerebellum of the mouse. Numbers without prefix indicate the nomenclature for the 5 -N-positive bands of Marani (1982) P-numbers on the left side refer to the nomenclature for corresponding Zebrin I-positive bands of Hawkes and Leclerc (1987). ANT = anterior lobe FLO = flocculus PFL = paraflocculus II-X = lobules...

Fig. 132. Transverse sections through lobules I-V of the anterior lobe of mouse cerebellum, reacted for 5 -nucleotidase. The 5 -nucleotidase-positive bands are numbered according to Marani (1986).

The numbering of 5 -nucleotidase-positive bands according to Marani (1986) and Hawkes and Leclerc s (1987) numbering system for the Zebrin-positive bands can be compared in Fig. 131 of the distribution of 5 -N in mouse cerebellum. 

Fig. 135. Photomicrographs of the ventral surfaee of the uvula of the cerebellum of the mouse in adjacent sections reacted with Zebrin I antibody (A) and for the presence of 5 -nueleotidase (B). Note the identical pattern of staining in both even though the borders of the 5 -nucleotidase staining (B) are less distinct. Q113 = mabQin, 5 N = 5 -nucleotidase. Eisenman and Hawkes (1989).

A major drawback of many studies of the chemical neuroanatomy is that they were conducted in only one species, the rat. There is extensive evidence for species differences in the distribution of the synthetizing enzyme of acetylcholine (ChAT), muscarinic cholinergic receptors and acetylcholinesterase (see Section 3.10.), and there is reason to assume that a similar interspecies variability exists for other transmitter systems. The expression of Zebrin by certain subpopulations of Purkinje cells, and the zonal patterns in the distribution of 5 -nucleotidase, only occur in certain species. It is a fortunate coincidence for the experimental neuroscientist that the Zebrin zonal pattern is expressed in rats, but in other species like the cat or macaque monkeys all Purkinje cells are Zebrin-immunoreactive. Many species-differences in the chemical neuroanatomy of the cerebellum may be due to the selectivity of the antibodies employed in the im-munocytochemical techniques, but other differences may be real and may reflect true variations in structure or in the transmission and second messenger systems of the cerebellum. 

Brown B, Epema A, Marani E (1986) Topography of acetylcholinesterase in the developing rabbit and cat cerebellum. In Topographic Histochemistry of the Cerebellum. 5 -Nucleotidase, Acetylcholinesterase, Immunology of FAL. Progr. Histochem. Cytochem., 16/4, 117-127. 

Marani E (1977) The subcellular distribution of 5 -nucleotidase activity in mouse cerebellum. Exp. Neurol, 57, 1042-1048. 

Marani E (1982a) Topographic enzyme histochemistry of the mammalian cerebellum, 5 -nucleotidase and acetylcholinesterase. Thesis, Leiden. 

Marani E (1982b) The ultrastructural organization of 5 -nucleotidase in the molecular layer of mouse cerebellum. In Bradford HF (Ed.), Neurotransmitter Interaction and Compartmentation. Plenum Press, New York, 558-572. 

Schoen SW, Graeber MB, Reddington M, Kreutzberg GW (1987) Light and electron microscopical im-munocytochemistry of 5 -nucleotidase in rat cerebellum. Histochemistry, 87, 107-113. 

Schoen SW, Graeber MB, Toth L, Kreuzberg GW (1988) 5 -Nucleotidase in postnatal ontogeny of rat cerebellum a marker for migrating nerve cells Dev. Brain Res., 39, 125-136. 

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