Firing Patterns Of Mice Medial Septum And Their Relationship With Hippocampus Theta Rhythm

The theta oscillation (4-12Hz) is a typical electrical synchronization activity of hippocampus local field potential, which is considered to be an important process of information integration in learning and memory, attention and motivation. It is still an open question that how hippocampal theta oscillation generates. Since there is no generator in hippocampus, researches have revealed that the generator could be in medial septum diagonal band of Broca nuclei(MS-DBB), where some theta related neurons are considered to be the pacemaker of hippocampal theta oscillation. The mechanism how these neurons are related to theta oscillation is still a mystery. To understand how MS-DBB neurons affect the generation of hippocampal theta rhythm, multi-channel in vivo recording in freely moving mouse is made to record neuronal activity simultaneously in hippocampus and MS-DBB. Combing with Granger Causality arithmetic, we are trying to reveal the relationship of MS-DBB neurons and hippocampal CA1 local field potential.58 neurons have been recorded in MS-DBB 41 neurons among them (approximately 70%) are phase locked to hippocampal theta oscillation. In addition, we classify the theta related neurons into two groups according to their firing patterns:Type 1 cells (n= 26),which we refer to as theta burst neurons. Type 2 cells (n= 15) are phase locked with theta oscillations without burst firing. Next, we sort Type 1 cells into 3 groups due to their firing patterns differences:Type 1A (n= 16) cells burst rhythmically, and more likely to fire in the rising phase of theta oscillation. Meanwhile, these cells are highly coherenced with theta rhythm (coherence= 0.64+0.05). Type 1B (n= 5) neurons also have burst activities with theta except that some single spikes interrupt burst interval, thus make them less rhythmic. However, Type 1B cells still have high coherence with theta oscillation (Coherence = 0.5±0.05). Compared with Type 1B cells, Type 1C cells have less intraburst spikes as well as long interburst duration. Through Granger Causality analysis of MS-DBB neurons and hippocampal local field potential, we found that the neurons and LFP have bothway Granger Causality over the threshold. Especially, some Type 1A neurons (n= 3) and Type 1B neurons (n= 2) have obvious Granger causal relationship with hippocampal theta activity (Unit-LFP:0.47±0.05; LFP-Unit:0.26±0.03). Other neurons of Type 1A (n= 9),Type 1B (n= 2) and Type 1C (n= 5) neurons are affected by hippocampal theta LFP (unit-LFP:0.14±0.02, LFP-Unit:0.40±0.04).Our research indicates that most of MS-DBB neurons are phase locked to hippocampal theta oscillation. Whose firing activities are highly correlated with theta band of hippocampal local field potential. Furthermore, Granger Causality analysis revealed that there are some neurons who have strong causal relationship with hippocampal theta rhythm. These neurons could take part in the generation of hippocampal theta rhythm.