ABSTRACT
<p><b>OBJECTIVE</b>To investigate the effects of smoking of dried leaves of Carica papaya (pawpaw) based on ethnopharmacological information which indicated that smoking of papaya leaves could influence motor performance and learning.</p><p><b>METHODS</b>Twenty-four rats were used for the study, and were grouped into four groups. Groups 1 served as the control (not exposed to papaya leaves smoke), while Groups 2, 3 and 4 were exposed to smoke from 6.25 g, 12.50 g and 18.75 g of dry pawpaw leaves respectively in a smoking chamber twice daily for 21 d with each exposure lasting for 3 min. Lastly, hippocampus was harvested in each group for histological study.</p><p><b>RESULTS</b>The results showed that there were significant (P<0.05) increases in mean of recall latencies of long-term spatial memory in the animal administered the high dose while the other groups had significantly (P<0.05) lower frequencies. Histological investigation showed signs of mild neural degeneration in high dose group and hypochromic appearance of the Nissl substance in all treated groups.</p><p><b>CONCLUSIONS</b>In conclusion, the findings from this study has demonstrated that smoking of papaya leaves has the ability to maintain an intact long-term spatial memory at all doses but retrieving such memory is faster with the low and medium dosages.</p>