Differential effects of lead and zinc on inhibitory avoidance learning in mice

We studied the effects of chronic intoxication with the heavy metals lead (Pb2+) and zinc (Zn2+) on memory formation in mice. Animals were intoxicated through drinking water during the pre- and postnatal periods and then tested in the step-through inhibitory avoidance memory task. Chronic postnatal intoxication with Pb2+ did not change the step-through latency values recorded during the 4 weeks of the test (ANOVA, P>0.05). In contrast, mice intoxicated during the prenatal period showed significantly reduced latency values when compared to the control group (day 1: q = 4.62, P<0.05; day 7: q = 4.42, P<0.05; day 14: q = 5.65, P<0.05; day 21: q = 3.96, P<0.05, and day 28: q = 6.09, P<0.05). Although chronic postnatal intoxication with Zn2+ did not alter a memory retention test performed 24 h after training, we noticed a gradual decrease in latency at subsequent 4-week intervals (F = 3.07, P<0.05), an effect that was not observed in the control or in the Pb2+-treated groups. These results suggest an impairment of memory formation by Pb2+ when the animals are exposed during the critical period of neurogenesis, while Zn2+ appears to facilitate learning extinction

Identification of efferent-stimulus-responding neurons in the earthwoem 3rd segmental nerve by Lucifer yellow-ch backfilling

The objective of the present study was to identifify the mechanism for the decreased efferent reflex response recorded extracellulary from an earthworm 3rd segmental nerve after the nerve had been cut. Four neurons which showed a correlated decrease in their efferent responses were identified in the ventral nerve cord by the broken-microelectrode-backfilling method using Lucifer Yellow-CH. The long processes of these neurons extended into the 3 rd nerve trunk.Thus teses neurons may neurons mayrepresent an efferent link in the this complicated reflex are