Properties of supraoptic magnocellular neurones isolated from the adult rat.

S H Oliet, C W Bourque
The Journal of Physiology. 1992-09-01; 455(1): 291-306
DOI: 10.1113/jphysiol.1992.sp019302

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1. J Physiol. 1992 Sep;455:291-306.

Properties of supraoptic magnocellular neurones isolated from the adult rat.

Oliet SH(1), Bourque CW.

Author information:
(1)Centre for Research in Neuroscience, Montreal General Hospital, P.Q., Canada.

1. Magnocellular neurosecretory cells (MNCs) were isolated from the supraoptic
nucleus of adult Long-Evans rats using an enzymatic procedure. Immunocytochemical
staining with antibodies against vasopressin and oxytocin revealed that MNCs can
be identified by size. The membrane properties of these cells were examined at
32-34 degrees C using intracellular recording methods. 2. Isolated MNCs displayed
a mean (+/- S.E.M.; n = 109) resting membrane potential of -64.1 +/- 1.0 mV, an
input resistance of 571 +/- 34 M omega, and a time constant of 8.7 +/- 0.4 ms.
Measurements of specific resistivity and input capacitance revealed that the soma
of these cells accounts for a mere 20% of their total somato-dendritic membrane
in situ. 3. Voltage-current relations measured near -60 mV were linear negative
to spike threshold. From more hyperpolarized membrane potentials, voltage
responses to depolarizing current steps displayed transient outward rectification
and delayed impulse discharge. 4. Action potentials (76.6 +/- 0.9 mV) triggered
from an apparent threshold of -59.3 +/- 0.1 mV broadened progressively at the
onset of spontaneous or current-evoked spike trains. Steady-state spike duration
increased as a logarithmic function of firing frequency with a maximum near 25
Hz. These effects were abolished in Ca(2+)-free solutions. 5. In all cells,
evoked spike trains were followed by a prolonged Ca(2+)-sensitive
after-hyperpolarization. In contrast, only a small proportion (16%) of MNCs
displayed spontaneous bursting activity or depolarizing after-potentials
following brief current-evoked bursts. 6. Isolated MNCs responded to amino acids
(glutamate and GABA) and to the neuropeptide cholecystokinin, indicating that
receptors for these neurotransmitters are expressed postsynaptically by MNCs and
are retained following dissociation. 7. Increasing the osmolality of the
superfusing solution by 5-30 mosmol kg-1 caused a membrane depolarization
associated with a decrease of input resistance and accelerated spontaneous spike
discharge in each of thirty-six MNCs tested. Current-clamp analysis suggested
that these responses resulted from the activation of a cationic conductance.
Excitatory effects of hyperosmolality were not observed in non-magnocellular
neurones (n = 6).

DOI: 10.1113/jphysiol.1992.sp019302
PMCID: PMC1175645
PMID: 1362442 [Indexed for MEDLINE]

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