Influence of lactation on motor activity and elevated plus maze behavior.

Lactating rats show less noise-induced freezing and fewer inhibitory responses on the 6th day post-delivery when submitted to water and food deprivation in a classical conflict paradigm. Lactating mice go more often to the illuminated chamber in a light-dark cage and stay longer in it than virgin females. The present study was designed to assess the influence of this physiological state, i.e. lactation, on the elevated plus maze (EPM) and open-field behavior in adult female rats. Total (TL) and central (CL) locomotion and rearing (RF) frequencies were measured in an open-field. Number of entries into the open and closed arms as well as the time spent in each of these arms were measured in the EPM. percent time spent and number of entries into the open arms were calculated and compared. In the open-field, TL was significantly decreased (115 +/- 10.6 vs 150 +/- 11.6) while CL and RF did not differ from those presented by virgin rats. In the EPM, lactating rats displayed a significant reduction in percent time spent (10.9 +/- 1.5 vs 17.4 +/- 2.3) in the open arms as well as a tendency to a reduction in percent entries into the open arms (35.7 +/- 4.7 vs 45.7 +/- 4.3). These results show that the physiological state of lactation modulates the open-field and EPM behaviors in rats.