Effect of Oestrus Upon Achilles Reflex Time. ∗

Several authors have remarked upon the relationship, in mammals, between the functional sex glands and behavior—general 1 and specific. 2 No work has been done on the relationship between the normal functional sex glands and the central nervous system. This report gives the influence of oestrus on the electromyographically determined Achilles reflex time. Eight normal female rats with known sex histories were followed through 18 consecutive cycles, varying from 1 to 4 cycles per individual, and reflex time determinations were taken during the active phase of the sex cycle—oestrus, and during the quiescent phase—dioestrus. Vaginal smears were made daily according to the technique of Long and Evans (1922) to determine the phase of the cycle. Our determination of the reflex time for either period was taken as the average of 5 to 7 consecutive jerks. The recording apparatus and technique has been fully described elsewhere 3 and need not be discussed here.

The average reflex time during the dioestrus interval was .0059 sec.; that for oestrus was .0079 sec., with an average difference between the 2 periods of .0019 sec. The average difference, though not large, is, we feel, significant, especially since it is between one-third to one-fourth of the longest reflex times, and, in all instances, nearly 4 times as great as the jerk to jerk variation of one testing.

Two typical readings are included:

There are several possible explanations of the decreased rate of reflex responses. One is that the sex gland during oestrus directly or indirectly causes the liberation of a substance which inhibits the passage of the nerve impulse somewhere along the arc. Another is that the impulse set up by the stimulus has greater radiation during oestrus and hence its appearance in the muscle is delayed.