Changes in morphology of dendritic spines on honeybee calycal interneurons associated with cumulative nursing and foraging experiences.

Using the rapid Golgi method, the morphology of dendritic spines was quantified in the calyxes of groups of newly emerged, nurse, and forager honeybees. These groups were studied because they represented distinct stages of behavioral development and cumulative experience which, according to recent vertebrate findings, may be associated with enlargement of the spine head and stem shortening. Measurements were made of spine density, overall spine length, stem length, maximum head width, and profile area using eyepiece micrometry and computer image analyses. The results indicated that none of the groups differed appreciably in spine density and overall spine length. Foragers did exhibit spines with markedly larger profile areas and shorter stems than those in newly emerged and nurse honeybees. However, nurses and foragers did not differ appreciably in spine head width, but both groups had markedly wider heads than the newly emerged group did. These findings suggest that elongated growth of the spine head and concomitant stem shortening is an incremental process affecting different portions of the spine population at different rates. In particular, the growth rate of most spines appears to accelerate during the foraging stage in which the diversity of sensory stimulation is greatest.