Indiana University Bloomington


Maternal effects in the development of a sexually dimorphic neuromuscular system

Early social contact between mother and offspring influences offspring neural development and reproductive behavior.  This project focuses on the effects of maternal care on the development of the spinal nucleus of the bulbocavernosus (SNB) of rats, a sexually dimorphic motoneuron population, which in males innervates muscles at the base of the penis that control copulatory penile reflexes.  Maternal licking of the perineal regions of offspring influences the development of the SNB, and consequently, adult copulatory behavior. 

For example, we have found that experimentally reducing maternal licking behavior produces a 50% regional decrease in adult dendritic length in the SNB of offspring.  Subsequent work has explored the possible mechanisms through which early maternal care influences the development of the SNB.  Reduced maternal licking likely alters the pattern of afferent activity that SNB motoneurons receive, potentially producing differential dendritic development.  We have found that cutaneous sensory afferents from the perineal skin terminate in the spinal cord in a biased distribution relative to the SNB dendritic arbor, suggesting that tactile stimulation via maternal licking could produce the regionally specific effects we have observed.  Using an artificial rearing paradigm, we found that both adult penile reflex behavior and SNB dendritic morphology of animals that received reduced stimulation are negatively affected.  Together, these results suggest that the tactile component of maternal licking is crucial to the development of the SNB and resultant sex behavior.