Glutamate ejection in the locus coeruleus enhances the perforant path-evoked population spike in the dentate gyrus

Messaoudi, Elhoucine, Kjetil Bårdsen, Bolek Srebro, and Clive R. Bramham. Acute intrahippocampal infusion of BDNF induces lasting potentiation of synaptic transmission in the rat dentategyrus. J. Neurophysiol. 79: 496–499, 1998. The effect of acuteintrahippocampal infusion of brain-derived neurotrophic factor (BDNF) on synaptic transmission in the dentate gyrus was investigated in urethan-anesthetized rats. Medial perforant path-evoked field potentials were recorded in the dentate hilus and BDNF-containing buffer was infused (4 μl, 25 min) immediately above the dentate molecular layer. BDNF led to a slowly developing increase of the field excitatory postsynaptic potential (fEPSP) slope and population spike amplitude. The potentiation either reached a plateau level at ∼2 h after BDNF infusion or continued to increase for the duration of experiment; the longest time point recorded was 10 h. Mean increases at 4 h after BDNF infusion were 62.2 and 224% for the fEPSP slope and population spike, respectively. No changes in responses were observed in controls receiving buffer medium only or buffer containing cytochrome C. BDNF-induced potentiation developed in the absence of epileptiform activity in the hippocampal electroencephalogram or changes in recurrent inhibition on granule cells as assessed by paired-pulse inhibition of the population spike. We conclude that exogenous BDNF induces a lasting potentiation of synaptic efficacy in the dentate gyrus of anesthetized adult rats.

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Phasic Boosting of Medial Perforant Path-Evoked Granule Cell Output Time-Locked to Spontaneous Dentate EEG Spikes in Awake Rats

Journal of Neurophysiology ◽

10.1152/jn.1998.79.6.2825 ◽

1998 ◽

Vol 79 (6) ◽

pp. 2825-2832 ◽

Cited By ~ 9

Author(s):

Clive R. Bramham

Keyword(s):

Dentate Gyrus ◽

Slow Wave ◽

Granule Cell ◽

Slow Wave Sleep ◽

Population Spike ◽

Perforant Path ◽

Evoked Responses ◽

Population Spike Amplitude ◽

Output Time ◽

Awake Rats

Bramham, Clive R. Phasic boosting of medial perforant path-evoked granule cell output time-locked to spontaneous dentate EEG spikes in awake rats. J. Neurophysiol. 79: 2825–2832, 1998. Dentate spikes (DSs) are positive-going field potential transients that occur intermittently in the hilar region of the dentate gyrus during alert wakefulness and slow-wave sleep. The function of dentate spikes is unknown; they have been suggested to be triggered by perforant path input and are associated with firing of hilar interneurons and inhibition of CA3 pyramidal cells. Here we investigated the effect of DSs on medial perforant path (MPP)-granule cell-evoked transmission in freely moving rats. The MPP was stimulated selectively in the angular bundle while evoked field potentials and the EEG were recorded with a vertical multielectrode array in the dentate gyrus. DSs were identified readily on the basis of their characteristic voltage-versus–depth profile, amplitude, duration, and state dependency. Using on-line detection of the DS peak, the timing of MPP stimulation relative to single DSs was controlled. DS-triggered evoked responses were compared with conventional, manually evoked responses in still-alert wakefulness (awake immobility) and, in some cases, slow-wave sleep. Input-output curves were obtained with stimulation on the positive DS peak (0 delay) and at delays of 50, 100, and 500 ms. Stimulation on the peak DS was associated with a significant increase in the population spike amplitude, a reduction in population spike latency, and a decrease in the field excitatory postsynaptic potential (fEPSP) slope, relative to manual stimulation. Granule cell excitability was enhanced markedly during DSs, as indicated by a mean 93% increase in the population spike amplitude and a leftward shift in the fEPSP-spike relation. Maximum effects occurred at the DS peak, and lasted between 50 and 100 ms. Paired-pulse inhibition of the population spike was unaffected, indicating intact recurrent inhibition during DSs. The results demonstrate enhancement of perforant path-evoked granule cell output time-locked to DSs. DSs therefore may function to intermittently boost excitatory transmission in the entorhinal cortex-dentate gyrus-CA3 circuit. Such a mechanism may be important in the natural induction of long-term potentiation in the dentate gyrus and CA3 regions.

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Idazoxan increases perforant path-evoked EPSP slope paired pulse inhibition and reduces perforant path-evoked population spike paired pulse facilitation in rat dentate gyrus

Brain Research ◽

10.1016/j.brainres.2005.12.020 ◽

2006 ◽

Vol 1072 (1) ◽

pp. 36-45 ◽

Cited By ~ 5

Author(s):

John Knight ◽

Carolyn W. Harley

Keyword(s):

Dentate Gyrus ◽

Population Spike ◽

Perforant Path ◽

Paired Pulse ◽

Paired Pulse Facilitation

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Repetitive Perforant-Path Stimulation Induces Epileptiform Bursts in Minislices of Dentate Gyrus From Rats With Kainate-Induced Epilepsy

Journal of Neurophysiology ◽

10.1152/jn.00456.2010 ◽

2011 ◽

Vol 105 (2) ◽

pp. 522-527 ◽

Cited By ~ 10

Author(s):

Li-Rong Shao ◽

F. Edward Dudek

Keyword(s):

Dentate Gyrus ◽

Field Potential ◽

Population Spike ◽

Perforant Path ◽

Excitatory Postsynaptic Potential ◽

Single Population ◽

Normal Medium ◽

Prolonged Duration ◽

Single Spike ◽

Hippocampal Theta

The epileptic hippocampus has an enhanced propensity for seizure generation, but how spontaneous seizures start is poorly understood. Using whole cell and field-potential recordings, this study explored whether repetitive perforant-path stimulation at physiological frequencies could induce epileptiform bursts in dentate gyrus minislices from rats with kainate-induced epilepsy. Control slices from saline-treated rats responded to single perforant-path stimulation with an excitatory postsynaptic potential (EPSP) and a single population spike in normal medium, and repetitive stimulation at different frequencies (0.1, 1, 2, 5, 10 Hz) did not cause significant increases in the responses. Most minislices (82%) from rats with kainate-induced epilepsy also responded to single perforant-path stimulation with an EPSP and a single population spike/action potential, but some slices (18%) had a more robust response with a prolonged duration and negative DC shift or responses with two to three population spikes. Repetitive perforant-path stimulation at 5–10 Hz, however, transformed the single-spike responses into epileptiform bursts with multiple spikes in half (52%) of the slices, while lower frequency (e.g., ≤1 Hz) stimulation failed to produce these changes. The emergence of epileptiform bursts was consistently associated with a negative field-potential DC shift and membrane depolarization. The results suggest that compared with the controls, the “gate” function of the dentate gyrus is compromised in rats with kainate-induced epilepsy, and epileptiform bursts (but not full-length seizure events) can be induced in minislices by repetitive synaptic stimulation at physiological frequencies in the range of hippocampal theta rhythm (i.e., 5–10 Hz).

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