Effect of cannula placement within the third ventricle on CSF-GnRH release during pulses. A, Mean (±sem) concentration of GnRH over the two 4-h periods for each of the eight ewes. It is evident that CSF harvested from the infundibular recess had the greatest GnRH concentration. B, Mean (±sem) GnRH pulse frequency in the CSF for the four animals in which CSF could be collected from all three cannulae. LH pulse frequency in the peripheral blood is also shown (gray bar). C, Mean (±sem) GnRH pulse amplitude in the CSF for the four animals in which CSF could be collected from all three cannulae. The optic recess data are noted by a black bar, infundibular recess data by a dashed bar, and pineal recess by a white bar. Differing letters indicate significant differences P < 0.05.