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Abstract
Previous studies suggest that the rostral corticomedial amygdala (CMA), particularly
the medial nucleus, is an important site where vomeronasal and olfactory stimuli critical
to male hamster copulatory behavior are processed. To test the possibility that mating
deficits seen after lesions of the rostrally-placed medial nucleus may be due to the
interruption of chemosensory afferents to more caudal areas, we injected tritiated
amino acids into the accessory and main olfactory bulbs of male hamsters in which
we had first produced bilateral electrolytic lesions or sham lesions in either the
rostral CMA or basolateral amygdala, and then observed mating behavior. Autoradiographic
analysis of "vomeronasal' projections from the accessory olfactory bulb and "olfactory'
projections from the main bulb, revealed that rostral CMA lesions which damaged the
medial nucleus and extended to the ventral surface of the brain (ventral lesions)
interrupted vomeronasal input to the more caudally-placed posteromedial cortical nucleus,
but spared olfactory inputs to adjacent caudal areas of the amygdala and piriform
lobe. In contrast, lesions which damaged a major portion of the medial nucleus but
left its ventral surface intact (dorsal lesions) spared both vomeronasal and olfactory
inputs to more caudal areas. Animals with both dorsal and ventral lesions failed to
mate postoperatively, whereas animals bearing sham lesions of basolateral amygdaloid
lesions, which, like dorsal lesions, spared caudally-directed chemosensory afferents,
continued to mate normally. We conclude that mating deficits seen after rostral CMA
lesions are due primarily to destruction of the medial nucleus.