Neuroanatomical and behavioral effects of a novel version of the cholinergic immunotoxin mu p75‐saporin in mice

Abstract

The selective lesion of basal forebrain cholinergic neurons (BFCNs) is an unestimable tool to study the implication of these neurons in cognition, an interest widely motivated by their degeneration in Alzheimer's disease. Here we evaluated the histochemical and behavioral effects of a selective lesion of BFCNs in C57BL/6J mice treated intracerebroventricularly (ICV) with a novel version of the immunotoxin mu p75-saporin (0.4 mug/mouse). There was a 100% postsurgical survival rate, no abnormal loss of weight, no disruption of sensorimotor coordination, and no noncognitive bias in a water-maze test. This immunotoxin induced a loss of choline acetyltransferase-positive neurons in the medial septum (-82%) and in the nucleus basalis (-55%). Preserved parvalbumine-immunostaining suggests that the lesion was specific to BFCNs. Septo-hippocampal and basalo-cortical projections of BFCNs degenerated as suggested by massive loss of acetylcholinesterase-positive staining in the hippocampus and the cortical mantle. Moreover, anticalbindin immunostaining showed no damage to cerebellar Purkinje cells. Lesioned mice displayed increased diurnal and nocturnal locomotor activity. Their spatial learning/memory performances in a water maze and in a Barnes maze were significantly impaired: learning was substantially slowed down, although not obliterated, and memory retention was altered. These behavioral consequences are comparable, with fewer side effects, to those reported after ICV 192 IgG-saporin in rats. In conclusion, the new version of mu p75-saporin provides a safe and powerful tool for BFCN lesion in mice.

Diffusion-weighted magnetic resonance imaging detection of basal forebrain cholinergic degeneration in a mouse model

“…In order to investigate this, we used a mouse model in which the toxin saporin, conjugated to an antibody to a receptor almost exclusively expressed by basal forebrain cholinergic neurons (p75 neurotrophin receptor; p75 NTR ), is injected into the ventricles (BergerSweeney et al, 2001). This treatment has been demonstrated to provide a robust model of the selective basal forebrain cholinergic neuron loss and behavioral consequences seen in Alzheimer's disease (Berger-Sweeney et al, 2001;Kokjohn and Roher, 2009;Moreau et al, 2008;Nilsson et al, 1992;Perry et al, 2001;Rossner, 1997). We hypothesized that all dMRI measures of the basal forebrain nuclei, together with the diffusion measures but not track number per se of septo-hippocampal tractograms, would be altered to reflect the neurodegeneration induced by this model.…”

Elimination of the vesicular acetylcholine transporter in the forebrain causes hyperactivity and deficits in spatial memory and long-term potentiation

“…In addition, spatial memory has also been suggested to depend on cholinergic activity (10), although there are numerous controversies surrounding which behaviors acetylcholine (ACh) regulates (11,12). Moreover, in few studies cholinergic denervation did not affect expression of LTP (13).…”

“…This is likely related to the fact that in many cases both noncholinergic and cholinergic projection neurons are destroyed, or that the lesions produced do not fully deplete cholinergic neurons. Moreover, most immunolesion experiments were performed initially in rats (15,16), and only recently immunotoxins have been developed for mice (11), a species in which genetic tools are available. In mice these toxins show poor selectivity depending on the dose used (11).…”

“…Moreover, most immunolesion experiments were performed initially in rats (15,16), and only recently immunotoxins have been developed for mice (11), a species in which genetic tools are available. In mice these toxins show poor selectivity depending on the dose used (11). In addition to these technical problems, cholinergic neurons usually release glutamate as a neurotransmitter with ACh (17,18), which complicates the interpretation of dysfunction using toxin-based methodologies that eliminate secretion of both neurotransmitters simultaneously.…”

“…Cholinergic tone has been associated with several memoryrelated functions (20,21), but depending on the approach and investigator, lesion of the medial septum cholinergic system caused varying degrees of spatial navigation impairment (11,12,16). Indeed, for some investigators cholinergic lesions did not cause impairment in spatial memory (15,23).…”