The lateral septum as a regulator of hippocampal theta oscillations and defensive behavior in rats.

Article date: 2015/12/15

PubMed ID: 1828866

Journal name: Journal of neurophysiology (ISSN: 1522-1598)

DOI: 10.1152/jn.00806.2014


Hippocampal theta oscillations are linked to various processes, including locomotion, learning and memory, and defense and affect. The lateral septum (LS) has been implicated in the generation of the hippocampal theta rhythm, but its precise role in this process is not well understood. Here, we investigated the effects of direct pharmacological inhibition or disinhibition of the dorsal LS (dLS) on the frequency of hippocampal theta activity elicited by stimulation of the reticular formation in urethane-anesthetized rats. We found that bilateral infusions of the GABAA receptor agonist muscimol into the dLS significantly increased theta frequency. Strikingly, intra-dLS infusions of the GABAA receptor antagonist GABAzine largely abolished reticularly elicited theta activity. We also locally injected these same compounds into the medial septum (MS) to test for neuroanatomical specificity. In contrast to the effects seen in the dLS, intra-MS infusions of muscimol had no effect on theta frequency, whereas intra-MS infusions of GABAzine increased theta frequency. Given the hypothesized role of hippocampal theta in behavioral defense, we also examined the effects of intra-dLS application of muscimol in two models of anxiety, the elevated plus maze and the novelty-induced suppression of feeding paradigm; both tests revealed clear, anxiolytic-like effects following muscimol infusions. The fact that dLS-muscimol increased theta frequency while also reducing anxiety-like behaviors challenges the influential theta suppression model of anxiolysis, which predicts a slowing of theta with anxiolytic compounds. More importantly, the experiments reveal a novel role of the LS, especially its dorsal aspects, as an important gating mechanism for the expression of theta oscillations in the rodent hippocampus.

Author List: Chee San-San A, Menard Janet L, Dringenberg Hans C

Publication Types: Journal Article; Research Support, Non-U.S. Gov't

Article Date: 2015/01/14

Substances mentioned in the article: GABA Agonists; GABA Antagonists; Pyridazines; Muscimol; gabazine;

Mesh terms: Animals; Anxiety/physiopathology; Defense Mechanisms; GABA Agonists/pharmacology; GABA Antagonists/pharmacology; Hippocampus/physiology; Male; Muscimol/pharmacology; Pyridazines/pharmacology; Rats; Rats, Long-Evans; Septal Nuclei/drug effects; Theta Rhythm;

Citations: - 2801253

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