Effect of selective cholinergic denervation on the serotonergic system: implications for learning and memory.
The cholinergic system has been widely implicated in cognitive processes and cholinergic loss is a classical hallmark in Alzheimer disease. Increasing evidence supports a role of the serotonergic system in cognition, possibly through a modulation of cholinergic activity. We compared selective cholinergic denervation by administration of the immunotoxin 192 IgG-saporin in the nucleus basalis of Meynert (NBM) with intracerebroventricular (ICV) lesions of the basal forebrain in male rats 7 days after lesioning. NBM lesions induced significant changes in cholinergic markers in the frontal cortex, whereas ICV lesions produced significant decreases in cholinergic markers both in the frontal cortex and hippocampus. Only ICV lesions lead to memory impairments in passive avoidance and Morris water maze tasks. Both models lead to reductions of serotonin levels in the frontal cortex. Similar changes in 5-hydroxytriptophan levels were observed, suggesting a downregulation of the rate-limiting enzyme for the synthesis of serotonin along with the cholinergic deficit. Neither 5-HT1A nor 5-HT1B receptors seem to mediate this process. These data imply that the serotonergic system in the frontal cortex can compensate for diminished cholinergic function and support the investigation of the serotonergic system as a therapeutic target to treat Alzheimer disease.
Garcia-Alloza
Monica
M
Department of Pharmacology, School of Medicine, Centre for Applied Medical Research, University of Navarra, Pamplona, Spain.
Zaldua
Natalia
N
Diez-Ariza
Monica
M
Marcos
Beatriz
B
Lasheras
Berta
B
Javier Gil-Bea
Francisco
F
Ramirez
Maria Javier
MJ
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D000911:Antibodies, Monoclonal / Q000008:administration & dosage; D001921:Brain / Q000187:drug effects; D003714:Denervation; D007150:Immunohistochemistry; D000922:Immunotoxins / Q000008:administration & dosage; D007276:Injections, Intraventricular; D007858:Learning / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008568:Memory / Q000187:drug effects / Q000502:physiology*; D017551:Microdialysis; D009699:N-Glycosyl Hydrolases / Q000008:administration & dosage; D009474:Neurons / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D011985:Receptors, Serotonin / Q000378:metabolism; D054789:Ribosome Inactivating Proteins, Type 1; D000076985:Saporins; D012701:Serotonin / Q000378:metabolism*
C085696:192 IgG-saporin; D000911:Antibodies, Monoclonal; D000922:Immunotoxins; D011985:Receptors, Serotonin; D054789:Ribosome Inactivating Proteins, Type 1; D012701:Serotonin; D009699:N-Glycosyl Hydrolases; D000076985:Saporins; D000109:Acetylcholine