supramammillary nucleus: Does it play a role in the mediation of hippocampal theta rhythm?

Recent evidence suggests that the supramammillary nucleus (SUM) is an important link from the pontine reticular formation (PRF) to the septum-hippocampus in the generation of hippocampal theta rhythm. I proposed: (1) injections of WGA-HRP into the SUM would produce retrograde labeling in PRF cells; (2) lesions of the SUM would produce a reduction in the frequency and amplitude of hippocampal theta rhythm; (3) injections of procaine into the SUM would attenuate the amplitude and reduce the frequency of reticular elicited theta rhythm. Although WGA-HRP injections in the SUM produced minimal labeling in the PRF, there were labeled cells in the central gray of the pons, and in the dorsal raphe and surrounding regions. I found that lesions of the SUM produced minimal changes in the frequency and amplitude of theta in the behaving animal but that injections of procaine attenuated both of these measures in the urethane anesthetized rat.