Septo–hippocampal interaction

Abstract

The septo–hippocampal pathway adjusts CA1 network excitability to different behavioral states and is crucially involved in theta rhythmogenesis. In the medial septum, cholinergic, glutamatergic and GABAergic neurons form a highly interconnected local network. Neurons of these three classes project to glutamatergic pyramidal neurons and different subsets of GABAergic neurons in the hippocampal CA1 region. From there, GABAergic neurons project back to the medial septum and form a feedback loop between the two remote brain areas. In vivo, the firing of GABAergic medial septal neurons is theta modulated, while theta modulation is not observed in cholinergic neurons. One prominent feature of glutamatergic neurons is the correlation of their firing rates to the animals running speed. The cellular diversity, the high local interconnectivity and different activity patterns of medial septal neurons during different behaviors complicate the functional dissection of this network. New technical advances help to define specific functions of individual cell classes. In this review, we seek to highlight recent findings and elucidate functional implications of the septo-hippocampal connectivity on the microcircuit scale.

Traumatic Brain Injury Preserves Firing Rates But Disrupts Laminar Oscillatory Coupling and Neuronal Entrainment in Hippocampal CA1

“…This methodology allowed us to localize activity to specific layers (allowing identification of specific afferent projections into CA1) as well as to explore the relationship between synchronized synaptic input and local neuronal firing patterns after TBI. Given that the medial septum (MS) is implicated in the generation and maintenance of theta oscillations (Müller and Remy, 2018), we also explored whether communication between the hippocampus and the reciprocally connected medial septum was altered after TBI.…”

Cholinergic Dysfunction Involvement in Chronic Cerebral Hypoperfusion-Induced Impairment of Medial Septum–dCA1 Neurocircuit in Rats

“…MS–dCA1 neurocircuit contains cholinergic and GABAergic projections. Functionally, the cholinergic and GABAergic projections mainly contribute to the regulation of hippocampal function and the post-synaptic potentials of septo-hippocampal pathway (Müller and Remy, 2018 ). When MS was stimulated, we could record a mixed excitatory and inhibitory potential in dCA1.…”

“…In vivo , an important function of septo-hippocampal pathway is adjusting the CA1 network excitability to different behavioral states (Müller and Remy, 2018 ). To evaluate the effect of CCH on septo-hippocampal function, we established the 2VO rat models and recorded the electrophysiological properties of pyramidal cell layer in dCA1 through stimulating MS. By recording and analyzing the I/O curves, we found a significantly decreased post-synaptic potential amplitude in the MS–dCA1 circuit of 2VO rats without affecting the kinetics of transmitter release and post-synaptic response process.…”

“…It has been well studied that the medial septum (MS) within basal forebrain is one of the brain regions that closely interact with hippocampal CA1. This interaction is a precise negative feedback adjustment system [septo-hippo-septal loop (SHSL)], which adjusts the CA1 network excitability to different behavioral states (Müller and Remy, 2018 ). Although SHSL is controlled by the synergy of cholinergic, glutamatergic, and GABAergic neurons together, convincing evidence has demonstrated that cholinergic circuit in SHSL places a center stage for normal executive and mnemonic functioning, and the loss of cholinergic signaling is inextricably linked with cognitive decline (Dutar et al, 1995 ; Teles-Grilo Ruivo and Mellor, 2013 ; Ballinger et al, 2016 ; Dannenberg et al, 2017 ; Solari and Hangya, 2018 ).…”

Neural stem cell transplantation improves learning and memory by protecting cholinergic neurons and restoring synaptic impairment in an amyloid precursor protein/presenilin 1 transgenic mouse model of Alzheimer's disease

“…in ad, the loss of cholinergic neurons in the basal forebrain leads to a decrease in the number of cholinergic fibers in the hippocampus and the neocortex (12). nevertheless, synaptic loss is the principal correlate of disease progression and loss of cholinergic neurons thus causing cognitive deficits (13). However, limited literature has reported the association between neural stem cell transplantation and basal forebrain cholinergic neurons.…”