Ps. Loupe et al., FR DISCRIMINATION-TRAINING EFFECTS IN SHR AND MICROENCEPHALIC RATS, Pharmacology, biochemistry and behavior, 51(4), 1995, pp. 869-876
Fixed-ratio (FR) discrimination learning in adult male spontaneously h
ypertensive rats (SHR), methylazoxymethanol-induced microencephalic Sp
rague-Dawley (MAM), and Sprague-Dawley control rats was examined. SHR
and MAM rats had little problem learning incrementally more difficult
FR discriminations (FR1 vs. FR16, FR4 vs. FR16, and FR8 vs. FR16) that
resulted in parallel increases in errors in all animals, and displaye
d only modest learning deficits during a subsequent FR4 vs. FR16 posit
ion reversal. When training involved nonincremental changes in difficu
lty (FR8 vs. FR16, FR4 vs. FR16, FR8 vs. FR16, FR12 vs. FR16, and FR14
vs. FR16), SHR and MAM rats evidenced relatively large learning defic
its during the initial FR8 vs. FR16 discrimination but had no difficul
ty with the last two discriminations. Furthermore, training selectivel
y and significantly elevated hippocampal weight in MAM rats. These fin
dings: a) question prior suggestions that MAM and SHR model separate h
uman developmental disabilities; b) indicate that manifestation of lea
rning deficits in even markedly brain-damaged organisms depends on ini
tial task difficulty and can be overcome by experience; and c) are the
first indicating that training-induced antagonism of prenatally induc
ed hippocampal hypoplasia and its consequences is possible.