Effects of the muscarinic antagonists atropine and pirenzepine on olfactory conditioning in the honeybee.

One-trial conditioning of the proboscis extension reflex (PER) in honeybees was used to examine the qualitative effects of two muscarinic antagonists, atropine and pirenzepine, on the acquisition and retrieval of memory following intracranial injection. The main result of this study is that atropine, at a relatively high concentration of 10(-2) M, impairs memory retrieval but not acquisition of memory after a single olfactory conditioning trial (at this concentration, there is no effect of atropine on the sensorimotor components of the PER). This result is in agreement with the effects of scopolamine, reported in a previously published article. Pirenzepine, at the same concentration as atropine, had no effect on either acquisition or retrieval of memory. These results suggest that blockade of muscarinic-like receptors, except those that bind to pirenzepine, induces solely an impairment of memory retrieval.