Interspecific Differences in the Reaction to Atropine and 
in the Histology of the Esophagi of the Common 
California Sea Hares of the Genus Aplysia 
Lindsay R. Winkler and Bernard E. Tilton 1 
During a study of the effects of certain cho- 
linergic agents on the tissues of Aplysia, it was 
noted that the esophagi of the two California 
species (A. calif ornica and A. vac carta) reacted 
divergently to atropine. This is of interest to 
both the taxonomy and physiology of the genus 
as well as potentially to a better understanding 
of the mode of action of atropine. Other drugs 
commonly known to show activity on muscle 
tissue were also tested on the two species to 
determine if any other interspecifically diver- 
gent reactions existed. These pharmacological 
reactions will be reported later. 
Botazzi (1898) observed the periodic con- 
tractions of the esophagus of the European 
Aplysia and made a thorough study of its phys- 
iology. The physiology of the crop was studied 
extensively by von Briicke (1905). Straub 
(1907) reported the reaction of the heart of an 
unspecified species of Aplysia to muscarine and 
noted the lack of atropine antagonism in the 
heart ventricle. Hogben (1924) studied the re- 
action of the crop of an European Aplysia to 
epinephrine. 
MATERIALS AND METHODS 
Small- to medium-size specimens of Aplysia 
(Neaplysia) calif ornica Cooper and Aplysia 
{Aplysia) vaccaria Winkler were collected dur- 
ing the summer months at Lunada Bay, Palos 
Verdes, Los Angeles Co., California. The ani- 
mals were packed in wet Pelvetia fastigata and 
transported to the laboratory where they were 
maintained in a 10-gal. salt water aquarium 
until needed. A Cole-Parmer model all-plastic 
impeller-type pump drew the water from the 
aquarium through a filter containing glass wool 
and activated charcoal and pumped it serially 
1 Department of Pharmacology, Loma Linda Uni- 
versity School of Medicine, Loma Linda, California. 
Manuscript received January 13, 1961. 
through two 5 gal. carboys maintained in a re- 
frigerator. It was thus possible to keep the water 
clean and cooled to approximately the tempera- 
ture of the intertidal environment of these ani- 
mals. Parsley obtained in the local market was 
eaten in quantity by A. calif ornica but was re- 
fused by A. vaccaria. Consequently all speci- 
mens of the latter were used as soon as prac- 
ticable. 
Animals were sacrificed by incising the entire 
length of the foot, turning the animal inside out 
and removing the esophagus after tying it at 
both ends. The esophagi were suspended from 
a plastic holder in conventional baths using 30 
ml. of sea water. The movable end of the esoph- 
agus was ligated to a Grass force-displacement 
transducer, which was connected to a Grass am- 
plifier-recorder. 
To identify the two types of excursions noted 
in the tracings, cross sections of esophagus tis- 
sue were tied on opposite sides of the ring thus 
formed so as to obtain tracings of the contrac- 
tions of the circular muscle with little or no 
effect from the longitudinally oriented tissue. At- 
ropine was used in 1: 1000 solution ( 1 mg/ml) 
in all cases. 
For histological examination both longitudi- 
nal and cross sections were made using standard 
techniques. These were stained with eosin and 
hematoxylin. Sections were also made of all the 
noticeably differentiated areas of the digestive 
tract. 
EXPERIMENTAL RESULTS 
The normal pattern of contraction as re- 
corded from the isolated esophagus consists pri- 
marily of comparatively rapid short excursions 
which vary in frequency and amplitude. These 
may be interspersed with occasional contractions 
of greater amplitude, especially in A. calif ornica 
(Fig. la). Since the latter contractions were ab- 
557 
