INTRODUCTION: Two notable targets of the pedunculopontine tegmental nucleus (PPN) circuitry, the substantia nigra (SN) and the ventral tegmental area (VTA), are implicated in locomotion and reward processing. A dysfunction of these regions occurs in Parkinson’s and related disorders as well as in various psychiatric conditions, and over the course of normal aging AIM(S): In the present study, we were interested in understanding NMDA-receptors involvement in the interactions between the PPN and SN/VTA midbrain complex. In order to obtain more insight into this process, we analyzed the number and the distribution of midbrain tyrosine hydroxylase positive cells (TH+). METHOD(S): All rats were implanted with bilateral stimulating electrodes in the VTA and with bilateral guide cannulas for intracerebral injections into the PPN. Immunohistochemistry for TH+ was used to measure the number of active dopaminergic neurons in midbrain (VTA-SN) of rats subjected to unilateral VTA electrical stimulation and local injection of MK‑801 (5 μg) or NMDA (3 μg) to the contralateral or ipsilateral hemispheres into the PPN (4 experimental groups). The control brains were from rats in which only the 14‑day unilateral electrical VTA‑stimulation was performed (control group). RESULTS: Immunohistochemical analysis revealed a decrease in the number of TH+ cells in the midbrain. When the main subdivisions of the VTA/SN were subjected to a separate analysis, a significantly lower number of TH+ cells were found in all experimental groups in the PBP (parabrachial pigmented nucleus), PB (paranigral nucleus) and SNc (SN, pars compacta), as compared to the control group. CONCLUSIONS: The level of NMDA receptor arousal in the PPN regulates the activity of the midbrain dopaminergic cells. FINANCIAL SUPPORT: The research was funded by the Polish National Science Center; decision no: DEC‑2013/09/N/NZ4/02195 and by the Faculty of Biology, University of Gdansk, Poland.
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