Effect of ipsilateral lesioning of the nucleus basalis magnocellularis and of L-alpha-glyceryl phosphorylcholine treatment on choline acetyltransferase and acetylcholinesterase in the rat fronto-parietal cortex

Effect of lesions of the nucleus basalis magnocellularis and of treatment with posatirelin on cholinergic neurotransmission enzymes in the rat cerebral cortex

The effect of 4 and 8 weeks of treatment with the thyrotropin releasing hormone (TRH), analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide), on the changes of cholinergic neurotransmission enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), caused by lesions of the nucleus basalis magnocellularis (NBM), was investigated in the rat frontal cortex. ChAT and AChE were demonstrated with immunohistochemical and histochemical techniques, respectively associated with image analysis and microdensitometry. Monolateral and bilateral lesions of NBM area caused a significant loss of ChAT-immunoreactive nerve cell bodies in the NBM, as well as a remarkable decrease of ChAT-immunoreactive fibres and of AChE reactivity in the frontal cortex ipsilateral to the lesion or of both sides, respectively. The number of ChAT-immunoreactive nerve cell bodies in the lesioned NBM was higher in posatirelin-treated rats for 8 weeks in comparison with control NBM-lesioned rats. Moreover, the compound increased the number of ChAT-immunoreactive fibres in the frontal cortex of monolaterally and bilaterally NBM-lesioned rats at 8 weeks after lesion, but was without effect on these fibres in sham-operated rats. The same is true for AChE reactivity, developed in the neuropil of the frontal cortex, which was restored in part by an 8-week treatment with posatirelin in NBM-lesioned rats. These findings suggest that treatment with posatirelin rescues cholinergic neurons of the NBM and cholinergic projections to the cerebral cortex affected by lesioning of the NBM. The functional relevance of these observations and their possible applications should be evaluated in future studies.

Multiple forms of the enzyme glycerophosphodiesterase are present in human brain

Brain levels of glycerophosphodiesters, including glycerophosphocholine (GPC) and glycerophosphoethanolamine (GPE), are altered in many human central nervous system disorders. Although much information is available on the enzymes responsible for the formation of these phospholipid metabolites, little information is known regarding their catabolism, by glycerophosphodiesterases, in human brain. In both autopsied and biopsied temporal cortex, a phosphocholine-producing glycerophosphodiesterase activity was observed. In the presence of 1 mM EDTA, the enzyme possessed a pH optimum of 9.0, while the addition of 5 mM zinc acetate shifted the pH optimum to 10.5. When assayed at pH 9.0 in the absence of zinc acetate, the Km and Vmax were 104 +/- 2 microM and 77 +/- 18 nmol/h/mg protein, respectively, while assaying at pH 10.5 in the presence of 5mM zinc acetate yielded a Km of 964 +/- 56 microM, and a Vmax of 534 +/- 114 nmol/h/mg protein. Furthermore, whereas submillimolar concentrations of zinc acetate stimulated the activity of the enzyme in a dose-dependent manner when assayed at pH 10.5 (EC50 =20.3 +/- 3.0 microM), this did not result in a reciprocal inhibition of glycerophosphocholine phosphodiesterase (GPC PD) activity when assayed at a more acidic pH. This may suggest that human brain contains two phosphocholine-producing GPC PD activities, differentiable by their sensitivity to zinc ions. An activity capable of hydrolyzing GPE to form phosphoethanolamine could not be detected in either biopsied or autopsied brain. However, a choline/ethanolamine-producing glycerophosphodiesterase activity could be readily detected in biopsied, but not autopsied brain. this novel enzyme possessed a neutral pH optimum and was dependent upon divalent cations for activity. In conclusion, human brain contains at least two different glycerophosphodiesterases, a phosphocholine, and a choline/ethanolamine-producing activity, only one of which can be detected in autopsied tissue. The results of previous studies measuring brain glycerophosphodiesterase activity in degenerative brain conditions may need to be reevaluated in the light of these observations.

Microanatomical and electrophysiological changes of the rat dentate gyrus caused by lesions of the nucleus basalis magnocellularis

The effect of unilateral or bilateral lesions of the nucleus basalis magnocellularis (NBM) on the dentate gyrus of the hippocampus were assessed using microanatomical and electrophysiological techniques. NBM is the main cholinergic basal forebrain nucleus that supplies the fronto-parietal cortex. Lesions were induced using the neurotoxin ibotenic acid or a radio-frequency system and did not affect glutamic acid decarboxylase activity both in the frontal cortex and in the hippocampus. At 4 weeks after lesioning, a loss of choline acetyltransferase (ChAT) activity and of ChAT-immunoreactive fibres was observed in the frontal cortex but not in the hippocampus and no changes in the density of granule neurons of the dentate gyrus or in the hippocampal long-term potentiation (LTP) were noticeable. At 8 weeks after lesioning the loss of both ChAT activity and of ChAT-immunoreactive fibres persisted in the frontal cortex of NBM-lesioned rats. Moreover, at this time a significant decrease in the density of granule neurons in the dentate gyrus accompanied by a reduced probability of dentate LTP induction were observed in both ibotenic acid- and radio-frequency-lesioned rats. These findings have shown that although NBM does not send direct cholinergic projections to the hippocampus, lesions of this cholinergic nucleus are accompanied by delayed neurodegenerative changes involving the dentate gyrus. This suggests the occurrence of indirect connections between NBM and the hippocampus, the functional relevance of which should be explored.