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Activation of tachykinin system in the pedunculopontine tegmental nucleus suppresses hippocampal theta rhythm in urethane-anesthetized rats

100%
Leszkowicz E., Trojniar W.
Acta Neurobiologiae Experimentalis
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2005
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vol. 65
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issue 3
373-386
EN
The pedunculopontine tegmental nucleus (PPN) is one of the reticular generators of the hippocampal theta rhythm. The PPN neuronal circuitry related to theta generation involves its cholinergic, GABA-ergic and glutamatergic components. Here we provide data indicating that the PPN tachykinin system may also be a part of this circuitry. In the experimental model of the tail-pinch elicited hippocampal theta in urethane-anesthetized rats (implanted with bilateral recording electrodes in the stratum moleculare of the upper blade of the dentate gyrus and with injection cannula unilaterally inserted into the PPN) it was found that intra-PPN microinjection of Substance P (SP) and [d-Pro2, d-Phe7, d-Trp9]-Substance P (DPDPDT) caused suppression of the theta and enhancement of the delta activity in the hippocampal EEG. Accordingly, there was approximately a 50% (SP) -70% (DPDPDT) decline of the peak power in the theta frequency range and a decrease by 0.4 Hz in the corresponding peak frequency (DPDPDT only) in both hippocampi. The circuitry through which SP exerts its effect in the PPN can be only hypothetical at present. We suggest SP-evoked activation (either direct or indirect through the glutamatergic inputs) of the GABA interneurons which may tonically inhibit PPN outputs to the other theta-relevant structures.
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Modulation of hippocampal theta rhythm by the opioid system of the pedunculopontine tegmental nucleus

81%
Leszkowicz E., Kusmierczak M., Matulewicz P., Trojniar W.
Acta Neurobiologiae Experimentalis
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2007
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vol. 67
|
issue 4
447-460
EN
The pedunculopontine tegmental nucleus (PPN) belongs to the brainstem system which synchronizes hippocampal activity. Theta relevant intra-PPN circuitry involves its cholinergic, GABA-ergic and glutamatergic neurons and Substance P as neuromodulator. Evidence that PPN opioid elements also modulate the hippocampal theta is provided here. In urethane-anesthetized rats a unilateral microinjection of morphine (MF) (1.5 and 5 micrograms) increased the maximal peak power of tail pinch-induced theta. The higher dose also increased the corresponding frequency. When the theta was evoked by intra-PPN injection of carbachol (10 micrograms), the addition of MF (5 micrograms) prolonged theta latency and shortened the duration of the theta. These effects of MF were blocked by naloxone (5 micrograms). The results obtained suggest that the PPN opioid system can enhance or suppress the hippocampal theta depending on the actual level of PPN activation.
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