Phase relations of rhythmic neuronal firing in the supramammillary nucleus and mammillary body to the hippocampal theta activity in urethane anesthetized rats
✍ Scribed by Bernat Kocsis; Robert P. Vertes
- Publisher
- John Wiley and Sons
- Year
- 1997
- Tongue
- English
- Weight
- 209 KB
- Volume
- 7
- Category
- Article
- ISSN
- 1050-9631
No coin nor oath required. For personal study only.
✦ Synopsis
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 heterogeneous 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°6 7) or negative peaks (2177°6 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 counterparts, fired on the rising (97°6 9) or falling segments (297°6 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°) 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°6 9, range 56-99°) 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.