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Received July 24, 2003
Revised August 15, 2003
Accepted after revision October 21, 2003
1 SUNY Downstate
* To whom correspondence should be addressed. E-mail: syoung{at}downstate.edu.
Activation of group I metabotropic glutamate receptors
(mGluRs) alters the firing patterns of individual CA3
pyramidal cells in guinea pig hippocampal slices.
Following addition of the selective group I agonist (S)-
3,5-dihydroxyphenylglycine (DHPG) to the bathing
solution, pyramidal cells initially firing regular,
single action potentials switched to firing in brief
bursts. This change in firing pattern resulted from
modulation by mGluRs of three afterpotentials. The
medium and slow afterhyperpolarizations (m and sAHPs)
were blocked by mGluR activation. In addition, a voltage-
dependent afterdepolarization (ADP) was induced.
Recordings from mutant mice lacking phospholipase C
1 (PLC
1) showed that mGluR block of the
mAHP, as well as induction of the ADP, depended on the
phosphoinositide hydrolysis pathway. Block of the sAHP,
however, was partly spared in the absence of PLC
1. Optical recordings of post-spike intracellular Ca2+
rises showed that mGluR block of the AHP was not
mediated by alterations of action potential-associated
Ca2+ increases (Ca2+ transients). The mGluR induction
of an ADP was also independent of any changes in the
Ca2+ transient. The mGluR-induced change in the firing
pattern of hippocampal pyramidal cells is thus the
result of multiple mechanisms, including suppression of
both medium and sAHPs and activation of an ADP, that act
together to produce a specific excitatory effect, namely
an increased likelihood that a single action potential
will lead immediately to one or more following action
potentials.
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