In vitro activation of the medial septum-diagonal band complex generates atropine-sensitive and atropine-resistant hippocampal theta rhythm: an investigation using a complete septohippocampal preparation.
The medial septum and diagonal band complex (MS-DB) is believed to play a key role in generating theta oscillations in the hippocampus, a phenomenon critical for learning and memory. Although the importance of the MS-DB in hippocampal theta rhythm generation is generally accepted, it remains to be determined whether the MS-DB alone can generate hippocampal oscillations or is only a transducer of rhythmic activity from other brain areas. Secondly, it is known that hippocampal theta rhythm can be separated into an atropine-sensitive and insensitive component. However, it remains to be established if the MS-DB can generate both types of rhythm. To answer these questions, we used a new in vitro rat septohippocampal preparation placed in a hermetically separated two side recording chamber. We showed that carbachol activation of the MS-DB generated large theta oscillations in the CA1 and CA3 regions of the hippocampus. These oscillations were blocked by applying either the GABA(A) receptor antagonist bicuculline or the AMPA/kainate antagonist DNQX to the hippocampus. Interestingly, the application of the muscarinic receptor antagonist atropine produced only a partial decrease in the amplitude, without modification of the frequency, of theta. These results show for the first time, that upon optimal excitation, the MS-DB alone is able to generate hippocampal oscillations in the theta frequency band. Moreover, these MS-DB generated theta oscillations are mediated by muscarinic and nonmuscarinic receptors and have a pharmacological profile similar to theta rhythm observed in awake animals.
Goutagny
Romain
R
Department of Psychiatry, Douglas Mental Health University Institute, McGill University, Montréal, Québec, Canada. romain.goutagny@douglas.mcgill.ca
Manseau
Frédéric
F
Jackson
Jesse
J
Danik
Marc
M
Williams
Sylvain
S
D000818:Animals; D001285:Atropine / Q000494:pharmacology*; D001640:Bicuculline / Q000494:pharmacology; D002217:Carbachol / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists; D018698:Glutamic Acid / Q000502:physiology; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D066298:In Vitro Techniques; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000502:physiology; D018092:Kainic Acid Receptors / Q000037:antagonists & inhibitors; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D012688:Septum Pellucidum / Q000187:drug effects* / Q000502:physiology; D013779:Tetrodotoxin / Q000494:pharmacology; D013826:Theta Rhythm / Q000187:drug effects*; D005680:gamma-Aminobutyric Acid / Q000502:physiology
D001285:Atropine; D001640:Bicuculline; D002217:Carbachol; D058787:GABA-A Receptor Antagonists; D018698:Glutamic Acid; D018727:Muscarinic Antagonists; D011810:Quinoxalines; D011963:Receptors, GABA-A; D018092:Kainic Acid Receptors; D011976:Receptors, Muscarinic; D013779:Tetrodotoxin; D005680:gamma-Aminobutyric Acid; C056723:FG 9041