Effects of dihydrokainate (DHK) on pSLA induced by 3 mM glutamate (4A) or 3 mM cocaine (4B). Planarians were treated for 5 min with glutamate or cocaine by itself or in combination with DHK. Data are expressed as mean pSLA ± S.E.M. versus concentration of DHK. **p < 0.01 and *p < 0.05 compared to the glutamate or cocaine alone group (i.e., ceftriaxone concentration of 0 mM) following identification of significant main effects for the DHK/glutamate [F(5, 42) = 10.89, p < 0.0001] and DHK/cocaine [F(5, 42) = 10.06, p < 0.0001] data sets. N = 8 planarians per group.