Rhythmic firing of medial septum non-cholinergic neurons.
The presence of theta rhythm (5-10 Hz) in the hippocampus has been shown to enable long-term potentiation, a synaptic mechanism which has been proposed to underlie learning and memory. Medial septum cholinergic and GABAergic neurons that project to the hippocampus have been hypothesized to play conjointly a major role in the genesis of this rhythm. Building upon previous studies that have established the electrophysiological criteria for distinguishing cholinergic and non-cholinergic neurons in this area, it is demonstrated here that medial septum non-cholinergic neurons, putatively GABAergic, have the ability to discharge in rhythmic clusters of action potentials occurring at frequencies ranging from 1 to 8 Hz. Within the clusters, the firing frequency of action potentials varied between 13 and 57 Hz in a voltage-dependent manner. In addition, small voltage-dependent subthreshold membrane potential oscillations (16-54 Hz) were observed between clusters. Both subthreshold oscillations and clusters were eliminated by tetrodotoxin at 1 microM. These results indicate that non-cholinergic medial septum neurons could convey to the hippocampus not only theta but also higher frequency rhythmicity in the beta-gamma range (20-60 Hz).
Serafin
M
M
Departement de Physiologie, CMU, Genève, Switzerland.
Williams
S
S
Khateb
A
A
Fort
P
P
Mühlethaler
M
M
D000818:Animals; D002217:Carbachol / Q000494:pharmacology*; D002799:Cholinergic Fibers / Q000502:physiology*; D006168:Guinea Pigs; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D012686:Septal Nuclei / Q000502:physiology*
D002217:Carbachol