A. Fine et al., LEARNING IMPAIRMENTS FOLLOWING INJECTION OF A SELECTIVE CHOLINERGIC IMMUNOTOXIN, ME20.4 IGG-SAPORIN, INTO THE BASAL NUCLEUS OF MEYNERT IN MONKEYS, Neuroscience, 81(2), 1997, pp. 331-343
Four groups of monkeys (Callithrix jacchus) were injected with saline
or increasing amounts of the immunotoxin, ME20.4 IgG-saporin, directly
into the basal nucleus of Meynert via a frontal trajectory which avoi
ded damage to the overlying basal ganglia. ME20.4 IgG binds to the pri
mate p75 low-affinity neurotrophin receptor; when the saporin deriviti
zed antibody is injected into the basal forebrain, it selectively dest
roys the magnocellular neurons of the basal nucleus of Meynert which a
re the cells of origin of the cholinergic projection to the neocortex.
The highest dose of ME20.4 IgG-saporin produced a significant impairm
ent on acquisition of a perceptually difficult visual discrimination.
There was no significant effect on retention of tasks learnt before or
after surgery, nor on concurrent acquisition of several perceptually
easy discriminations or serial reversal of an easy discrimination. The
se results suggest that the impairment is not due to visual, motor or
motivational difficulties and does not consist of difficulties with th
e formation of reward associations. Rather the impairment is largely c
onfined to acquisition of perceptual discriminations. There was a sign
ificant correlation between the density of ME20.4 immunostaining in th
e basal nucleus of Meynert and the density of acetylcholinesterase his
tochemical staining in the frontal and temporal cortex and an inverse
correlation between both of these and the degree of learning impairmen
t in the animals. Lesioned animals also showed significant impairment
on acquisition and reversal of perceptually easy discriminations when
treated with a dose of scopolamine which did not impair performance in
control animals. These results provide further evidence that cortical
cholinergic neurotransmission contributes to certain forms of learnin
g. The availability of a selective cholinergic immunotoxin effective i
n primates provides an important new tool for the study of cholinergic
function and its involvement in ageing, Alzheimer's disease and other
pathological states. (C) 1997 IBRO. Published by Elsevier Science Ltd
.