Ablations of lumbar epaxial musculature: effects on lordosis behavior of female rats.

Ablations of lateral longissimus, medial longissimus, and the lumbar transversospinalis system were performed singly and sequentially on female albino rats. Animals were tested postoperatively with males and by manual stimulation for lordosis. In tests with males, the strength of lordosis was rated specifically with respect to the extent of rump elevation; in manual stimulation tests, rating was based on the full lordotic response. Animals were also tested for the ability to cross a balance beam as an indication of the general status of the animals' posture and locomotion. The data from tests with males proved more sensitive in showing up effects of the ablations on lordosis. Lateral longissimus ablations and transversospinalis ablations led predictably to worsened lordosis. Medial longissimus ablations did not significantly affect lordosis. The manual stimulation data were consistent with the data obtained in tests with males. Ablated animals were not impaired on the balance beam test. The results indicate that lateral longissimus and the lumbar transversospinalis system are major participants in the rump elevation of lordosis, an early and biologically important component of the lordotic response. This information permits focus on lateral longissimus and the lumbar transversospinalis system in the investigation of the neural control of lordosis.