Summary
An in vitro brain slice preparation of the electrosensory lateral line lobe (ELL) of weakly electric fish was developed. The morphology of this slice was studied and revealed that most ELL neurons and synapses retained their normal appearance for at least 10 h in vitro. The electrophysiological characteristics of the main ELL output neurons, the pyramidal cells, were measured. Extracellular electrode recordings demonstrated that pyramidal cells are capable of spontaneous, rhythmic spike activity. Intracellular recordings showed that intrinsic oscillations in membrane potential underlie the bursting behavior. The majority of pyramidal cells respond to depolarizing current pulses with an initial lag in spike firing followed by a non-accommodating, higher frequency spike train.
Time and voltage-dependent properties of pyramidal cell responsiveness, as well as the effects of pharmacological blocking agents indicated that rhythmic activity and repetitive firing are dominated by a persistent, subthreshold sodium conductance (gNa) which activates at depolarized levels and is the driving force behind the membrane potential oscillations and the sustained (non-accommodating) spike firing. In addition, a transient, outward potassium conductance (gA) is responsible for the lag in spike firing by acting as a ‘brake’ during the initial 50–200 ms of a depolarizing stimulus.
Calcium currents and calcium-dependent potassium conductance add to the interval between spontaneous bursts but appear insufficient for spike frequency accommodation.
The in vitro behaviour of pyramidal cells differs substantially from the behaviour of the same cell type in vivo. These observations raise possibilities that intrinsic membrane properties together with local synaptic interactions may regulate pyramidal cell responsiveness.
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Abbreviations
- ACSF :
-
artificial cerebrospinal fluid
- 4-AP :
-
4-amino-pyridine
- BP :
-
basilar pyramidal cell
- DML :
-
dorsal molecular layer
- EGTA :
-
ethyleneglycol-bis(B-aminoethylether)-N,N′tetraacetic acid
- ELL :
-
electrosensory lateral line lobe
- EOD :
-
electric organ discharge
- EPSP :
-
excitatory postsynaptic potential
- FPP :
-
fast prepotential
- IPSP :
-
inhibitory postsynaptic potential
- LF :
-
Lucifer Yellow
- NBP :
-
non-basilar pyramidal cell
- Rin :
-
input resistance
- SP :
-
slow potential
- TEA :
-
tetraethyl ammonium
- tsf :
-
tractus stratum fibrosum
- TTX :
-
tetrodotoxin
- Vm :
-
membrane potential
- VML :
-
ventral molecular layer
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Mathieson, W.B., Maler, L. Morphological and electrophysiological properties of a novel in vitro preparation: the electrosensory lateral line lobe brain slice. J. Comp. Physiol. 163, 489–506 (1988). https://doi.org/10.1007/BF00604903
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DOI: https://doi.org/10.1007/BF00604903