Alteration of neuronal nitric oxide synthase activity and expression in the cerebellum and the forebrain of microencephalic rats.
Microencephalic rats were obtained through gestational (for the forebrain) or neonatal (for the cerebellum) administration of the DNA-alkylating agent methylazoxymethanol acetate (MAM), which selectively kills dividing cells during neurogenesis. In the microencephalic cerebellum the specific activity of calcium-dependent nitric oxide synthase (NOS) was decreased by 35-40% at 12, 28 and 70 days of age. Other neurochemical markers not related to granule cells (the neuronal population selectively compromised by neonatal MAM treatment), choline acetyltransferase (ChAT) and glutamate decarboxylase (GAD) were not decreased, but actually increased when determined as specific activity. In agreement with the decreased catalytic activity measured in the tube, the expression of neuronal NOS protein was attenuated as judged from immunohistochemistry and Western blotting. In the microencephalic forebrain, the specific calcium-dependent NOS activity measured in homogenates of the whole hemisphere was significantly increased as compared to normal animals. Accordingly, immunohistochemistry for neuronal NOS, as well as NADPH-diaphorase histochemistry revealed an apparent increase in the density of strongly reactive neurons in the underdeveloped cortex and striatum of microencephalic rats. The results reported here demonstrate that permanent alterations of neuronal NOS activity and expression occur when the development of the brain and its neuronal circuits are severely compromised. Furthermore, the permanent downregulation of neuronal NOS in the cerebellum of microencephalic rats may be exploited for the study of the role of NO in mechanisms of synaptic plasticity such as long term depression (LTD).
Tregnago
M
M
Department of Biology, University of Bologna, Via Selmi 3, 40126 Bologna, Italy.
Virgili
M
M
Monti
B
B
Guarnieri
T
T
Contestabile
A
A
D000367:Age Factors; D000818:Animals; D000831:Animals, Newborn; D002531:Cerebellum / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D008297:Male; D008746:Methylazoxymethanol Acetate / Q000008:administration & dosage; D008831:Microcephaly / Q000139:chemically induced / Q000201:enzymology* / Q000473:pathology; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology* / Q000473:pathology; D019001:Nitric Oxide Synthase / Q000096:biosynthesis / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D009929:Organ Size / Q000187:drug effects; D016548:Prosencephalon / Q000187:drug effects / Q000201:enzymology* / Q000473:pathology; D051381:Rats; D017208:Rats, Wistar
D008746:Methylazoxymethanol Acetate; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat