title: Phase relations of rhythmic neuronal firing in the supramammillary nucleus and mammillary body to the hippocampal theta activity in urethane anesthetized rats.
abstract: Structures in the caudal diencephalon including the posterior hypothalamic nucleus, the supramammillary nucleus (SUM) and the nuclei of the mammillary body (MB) occupy a strategic position in the crossroads of ascending and descending traffic between the brainstem and the limbic forebrain (septum/hippocampus). In this study we analyzed the phase relations of rhythmically discharging SUM/MB cells to hippocampal theta rhythm in urethane anesthetized rats with a dual aim of separating different functional types of SUM and MB neurons and characterizing their coupling to septohippocampal theta oscillators. We found that rhythmically firing neurons in the SUM/MB represent a functionally heterogenous population of cells that are coupled with forebrain theta oscillators at different preferred phases. Based on their phase relations to hippocampal theta four groups of rhythmic SUM/MB cells were identified. Neurons of the first and second groups fired out-of-phase relative to each other and synchronously with the positive (8 degrees +/- 7) or negative peaks (-177 degrees +/- 7) of theta field activity in the hippocampus, recorded above the CA1 pyramidal layer. Cells of the other two groups, also forming out-of-phase counter-parts, fired on the rising (97 degrees +/- 9) or falling segments (-97 degrees +/- 6) of CA1 theta waves. The peaks in the phase distribution histogram were well separated, and the empty zones between them were wider (40-70 degrees) than those comprising the phase data for different groups. The variations of phase values for individual neurons, when tested during several theta epochs, did not exceed the range of a single group. Theta field potentials were also recorded in the SUM/MB and were advanced by one quarter of the cycle (79 degrees +/- 9, range 56-99 degrees) relative to CA1 theta oscillations. The present results indicate that, similar to other theta-generating structures, rhythmically firing neurons can be classified on the basis of their phase relations in the SUM/MB as well. Different classes of SUM/MB neurons might play different roles in generating and/or transmitting theta rhythmic activity of the limbic system.
authors.affiliation: Department of Physiology, National Institute of Neurosurgery, Budapest, Hungary. kocsber@mailer.oiti.hu
authors.forename: B
authors.initials: B
authors.lastname: Kocsis
authors.forename: R P
authors.initials: RP
authors.lastname: Vertes
mesh_terms: D018686:Anesthetics, Intravenous; D000818:Animals; D001683:Biological Clocks / Q000502:physiology; D004027:Diencephalon / Q000502:physiology*; D006624:Hippocampus / Q000502:physiology*; D008297:Male; D008326:Mammillary Bodies / Q000502:physiology*; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013826:Theta Rhythm; D014520:Urethane
chemical_list: D018686:Anesthetics, Intravenous; D014520:Urethane