Cholecystokinin-8 protects central cholinergic neurons against fimbria-fornix lesion through the up-regulation of nerve growth factor synthesis

Abstract

In this study, we demonstrate that cholecystokinin-8 (CCK-8) induces an increase in both nerve growth factor (NGF) protein and NGF mRNA in mouse cortex and hippocampus when i.p. injected at physiological doses. By using fimbria-fornix-lesioned mice, we have also demonstrated that repeated CCK-8 i.p. injections result in recovery of lesion-induced NGF deficit in septum and restore the baseline NGF levels in hippocampus and cortex. Parallel to the effects on NGF, CCK-8 increases choline acetyltransferase (Chat) activity in forebrain when injected in unlesioned mice and counteract the septo-hippocampal Chat alterations in fimbria-fornix-lesioned mice. To assess the NGF involvement in the mechanism by which CCK-8 induces brain Chat, NGF antibody was administrated intracerebrally to saline- and CCK-8-injected mice. We observe that pretreatment with NGF antibody causes a marked reduction of NGF and Chat activity in septum and hippocampus of both saline- and CCK-8-injected mice. This evidence indicates that the CCK-8 effects on cholinergic cells are mediated through the synthesis and release of NGF. Taken together, our results suggest that peripheral administration of CCK-8 may represent a potential experimental model for investigating the effects of endogenous NGF up-regulation on diseases associated with altered brain cholinergic functions.

Figure 1

NGF mRNA detected by using in situ hybridization histochemistry in the hippocampus of adult mice receiving saline (a) or CCK-8 (b) injections. Note the increase of NGF mRNA labeling in the CA3 hippocampal area of the CCK-8-treated mice. Specific NGF mRNA expression was confirmed by specificity test including digestion of mRNA with RNase A before hybridization and hybridization with sense NGF probe, which resulted in the absence of hybridization signals (c). (Magnification ×15.)

Figure 2

(a–d) Immunohistochemical localization of Chat-positive neurons in the septum and Broca’s bands of fimbria–fornix-lesioned mice receiving saline (a) or CCK-8 (b) injections. (×50). c and d show the high magnification (×150) of septal Chat-immunopositive neurons of fimbria–fornix-lesioned mice injected with saline or CCK-8, respectively.

Figure 3

Effects of fimbria–fornix lesion, Ab-NGF intracerebroventricular treatment, and/or CCK-8 injections on septal and hippocampal Chat activity. The bars represent the percent difference ± SSE with respect to the Chat values detected in the septum and hippocampus of the control mice (=100%). No significant changes were noted in the Chat activity in false-operated mice and after intracerebroventricular injection with saline (data not shown). ∗∗, P < 0.01; ∗∗∗, P < 0.001 vs. control. ⦵⦵, P < 0.01; ⦵⦵⦵, P < 0.001 vs. both control and fimbria–fornix-lesioned mice receiving saline.