This document describes two experiments on the effects of eserine and d-tubocurarine on acetylcholine-induced contractions of the frog rectus muscle. In the first experiment, eserine is added to the muscle bath and potentiates the effect of acetylcholine by inhibiting cholinesterases and allowing acetylcholine to accumulate at the motor end plate. In the second experiment, d-tubocurarine is shown to block the stimulatory action of acetylcholine on contractions of the frog rectus muscle when added before acetylcholine.

1. Effect Of Eserine On The Action Of Acetyl
Choline On Frog Rectus Muscle

2. Aim
 To determine the action of eserine on the action of Acetyl Choline on
the frog rectus

3. Apparatus
 Recording Drum or Kymograph
 Stand with lever
 Bent glass tube
 Frog dissection instruments

4. Procedure
 A pitched frog dissected and rectus abdominis exposed
 Lower end is fastened to bent glass tube
 Muscle immersed in beaker containing ringer
 Two normal contractions are recorded with interval of 3 min
 Eserine is added to medium and amplitude of contraction is observed

5. Observation
 Observations are recorded on recording drum and interpreted

6. Inference
 Eserine potentiates the effect of Acetylcholine on muscle
 It inhibits both true and pseudo cholinesterase
 Causes accumulation of choline at motor end plate and hence
increased amplitude of contraction

7. Effect Of d-Tubocurarine On The Action Of
Acetyl Choline On Frog Rectus Muscle

8. Aim
 To know the effects of d-Tubocurarine on Acetylcholine contractions
of frog rectus muscle

9. Apparatus
 Kymograph or Recording drum
 Frog dissection instruments
 Oxygen tube
 Aerator
 Simple lever

10. Solutions
 Frog ringer solution ( Nacl : 9gm, Kcl : 0.42 gm, Cacl2 : 0.24gm,
NaHCo3 :0.5 gm, Distilled Water : 1.4 lit
 Acetylcholine 1microgram/ml
 d-Tubocurarine 2 microgram/ml

11. Dissection
 A pitched frog is laid on a plate.
 Skin of the abdominal wall is cut and open.
 Identify the horizontal ladder like fibrous bands of rectus abdominis
muscle.
 Separate both muscles from the abdominal wall.
 Pass threads underneath the muscle.
 Tie the upper ends and lower ends.

12.  Swipe off the upper end with a piece of xiphisternum and lower end with pubic
attachment.
 The muscle with threads is kept in a beaker with lower end is tied to the
oxygen tube and upper end to the simple lever.
 It has a counter weight or load of 1.4gm using plasticine.
 A beaker of ringer solution is kept under the oxygen tube and oxygen is
allowed to pass.
 Leave the preparation for half an hour.
 Put sufficient load so that the contractions will be able to raise the lever
Dissection

13. Procedure
 The drum is started and is allowed to rotate for 15 sec
 After 15 sec, the ringer solution is changed with Acetylcholine solution.
 After 90 sec, it is replaced with frog ringer solution.
 The muscle that contracts during Ach exposure, slowly relaxes and comes to
original position
 Repeat the process until you get equal contractions with Ach.
 Now immerse the muscle in d-Tc solution for 30 sec
 Replace with Ach and repeat contractions
 If 10 micrograms of d-Tc is given, complete depression of Ach contraction is seen

14. Observation
 Stimulatory action of Ach on rectus abdominis muscle
 Blocking action of curare or d-Tc on Ach induced contractions of
rectus muscle