Parvalbumin-immunoreactive, fast-spiking neurons in the medial septum/diagonal band complex of the rat: intracellular recordings in vitro.
The medial septum/diagonal band complex is composed predominantly of cholinergic and GABAergic neurons, and it projects to the hippocampal formation. A proportion of the GABAergic neurons contain parvalbumin, a calcium-binding protein that has previously been localized in fast-spiking, non-accommodating GABAergic neurons in the cerebral cortex and neostriatum. The aim of the present study was to determine whether parvalbumin is localized preferentially in a similar electrophysiological class of neuron in the medial septum/diagonal band complex. The study was carried out using in vitro intracellular recording, intracellular biocytin filling and parvalbumin immunocytochemistry. Three main classes of neurons were identified according to standard criteria: burst-firing, slow-firing and fast-firing neuronal populations. The fast-firing neurons were subdivided into two subpopulations based on whether or not they displayed accommodation. The fast-spiking, non-accommodating cells were furthermore found to be spontaneously active at resting potentials, and to possess action potentials of significantly (P < 0.05) shorter duration (half width: 0.61 +/- 0.12 ms) than those of the regular-spiking, accommodating neurons (1.0 +/- 0.34 ms). Of the neurons that were successfully filled with biocytin and processed for parvalbumin immunoreactivity, 82% of the fast-spiking, non-accommodating cells possessed parvalbumin immunoreactivity, while none of the regular-spiking, accommodating neurons were found to be immunoreactive for parvalbumin. The slow-firing neurons, shown previously to be cholinergic, did not stain for parvalbumin immunoreactivity, in agreement with studies showing parvalbumin to be localized solely in GABAergic neurons in the medial septum/diagonal band complex. In conclusion, these findings suggest the presence of a previously uncharacterized population of neurons in the medial septum/diagonal band complex that generate high-frequency, non-adaptive discharge. This property correlates with the localization of parvalbumin in these neurons, which suggests that parvalbumin fulfils the same role in the medial septum/diagonal band complex that it does in other parts of the brain. The fast-spiking neurons in the medial septum/diagonal band complex may play an essential role in the GABAergic influence of the septum on the hippocampal formation.
School of Biomedical Sciences, University of Leeds, UK.
N P
NP
Morris
S J
SJ
Harris
Z
Z
Henderson
D000200:Action Potentials / Q000502:physiology*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000032:analysis* / Q000502:physiology; D002799:Cholinergic Fibers / Q000737:chemistry / Q000502:physiology; D008032:Limbic System / Q000737:chemistry* / Q000502:physiology; D008239:Lysine / Q000031:analogs & derivatives / Q000032:analysis; D009419:Nerve Tissue Proteins / Q000032:analysis* / Q000502:physiology; D009474:Neurons / Q000737:chemistry* / Q000502:physiology; D010320:Parvalbumins / Q000032:analysis* / Q000502:physiology; D051381:Rats
D002135:Calcium-Binding Proteins; D009419:Nerve Tissue Proteins; D010320:Parvalbumins; C013411:biocytin; D008239:Lysine