1. Behavioral Effects of Muscarinic Agonists and Antagonists on Flinders Sensitive Line Rats
Heather Cornett2, James Woods, Ph.D.1, Gail Winger, Ph.D1.
(1) University of Michigan, Department of Pharmacology, (2) College of Literature, Science, and the Arts,
University of Michigan, Ann Arbor, MI, USA
ABSTRACT
The Flinders Sensitive Line (FSL) animal model of
depression has been widely used to test well-known
antidepressants. In contrast to tolerant, normal animals, FSL
animals are more sensitive to the behavioral and hormonal effects
of muscarinic agonists and have elevated muscarinic receptors. The
primary basis for this increased sensitivity of the FSL animal is
that they have a greater number of muscarinic receptors than
normal animals. This initiative strives to determine what
physiological and/or neurological explanation there is for these
significant differences between FSL animals and normal animals.
This is accomplished by analyzing rate of response patterns in
order to gain a better understanding of the central drug effects on
both animal groups. Using operant conditioning in collaboration
with the injection of designated muscarinic agonists and
antagonists, the rate of responding of each rat was measured. It
was expected that when given equal doses of a muscarinic agonist
or antagonist, FSL rats show suppressed rates of responding,
because they are more sensitive to that drug. This hypothesis was
supported by observing rates of responding for muscarinic agonists
Arecoline and L670,548, where FSL animals showed greater
suppression in response rates than Sprague Dawley (SD) animals.
However, when given equal doses of muscarinic antagonists
Atropine and L687,306, SD animals were more suppressed than
FSL animals. Doses of diazepam were shown to have less of a
suppression effect on FSL animals than normal animals.
BACKGROUND
METHODS
• When contrasted with SD rats, FSL rats exhibit “depression-
like” qualities such as reduced body weight, elevated rapid eye-
movement during REM sleep, cognitive disabilities, and reduced
locomotor activity.
• By injecting both types of animals with various muscarinic
agonists and antagonists, the behavioral differences in the FSL
animals and normal animals are able to be observed.
• Acetylcholine is a neurotransmitter that binds to muscarinic
receptors. These receptors send messages by using the
acetylcholine neurotransmitter.
• A muscarinic agonist is a drug that mimics the actions of
acetylcholine by stimulating the acetylcholine receptors. A
muscarinic antagonist is an anticholinergic agent that blocks and
inhibits the activity of the muscarinic acetylcholine receptor.
• This research predominantly focuses on the effects of these
muscarinic agonists and antagonists on the brains of FSL and
normal animals.
• Diazepam is a drug that works at GABA receptors which reside
outside of the muscarinic system.
Subjects - 6 male SD rats and 6 male FSL rats
Testing Procedure - Each animal is injected with one of the
following drugs with corresponding pre-treatment times (PTT):
0.56 or 1.0 mg/kg Arecoline - 0min PTT
0.003 mg/kg L670,548 - 15min PTT
1.0 mg/kg Atropine - 15min PTT
0.01 mg/kg L687,306 - 0min PTT
3.0, 5.6, or 10.0 mg/kg Diazepam – 30min PTT
Animals are placed in operant conditioning boxes following their
PTT. Over the course of five components consisting of five minutes
each, each animal’s rate of responding per second is calculated and
recorded
Analysis - Each individual animal’s average per 25-minute period is
calculated. The average FSL animal’s rate of responding
(responses/second) is compared to that of the SD animals for each of
the five components.
RESULTS - ANTAGONISTS
RESULTS - AGONISTS
A.
Fig. A – When given 1.0 mg/kg Atropine with a 15 minute PTT, FSL rats had
higher rates of responding than SD rats
B.
E.
C.
Fig. B – When given 0.01 mg/kg L687,306 with no PTT, there was an
insignificant difference between FSL and SD rates of response
Fig. C – When given 0.56 mg/kg Arecoline with no PTT, FSL rats showed
lower rates of responding than SD rats
D.
Fig. D – When given 1.0 mg/kg Arecoline with no PTT, FSL rats showed
lower rates of responding than SD rats
Fig. E – When given 0.003 mg/kg L670,548 with no PTT, FSL rats showed
lower rates of responding than SD rats
CONCLUSION – FUTURE STUDY
• FSL rats were seen to be more sensitive to muscarinic agonists
than SD rats, which was evident in their heavily suppressed rates
of responding. This supported the initial hypothesis.
• When given a muscarinic antagonist, FSL rats were not suppressed
more than SD rats, and the data shows them having higher, or
nearly equal, response rates. This contradicts the initial hypothesis.
• FSL rats were less affected by Diazepam than SD rats, which is
interesting because this drug does not work at muscarinic
receptors.
• Further research will strive to solidify these claims, investigate
differences between the animals outside of the muscarinic system,
and work to understand the genetic differences of FSL rats to SD
rats.