It was recently shown in the olfactory bulb (OB) that the response to olfactory stimulation might be related to local reinforcement mechanisms involved in discrimination of different odors. Therefore, it seemed interesting to study the effects of several drugs of abuse on the release of dopamine (DA) in the OB. Nicotine, amphetamine, 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy"), and cocaine at 37°C increased the release of [ 3H] DA from olfactory bulb slice preparations of the rats. While nicotine, amphetamine, and MDMA directly evoked DA release, cocaine, by inhibiting the reuptake processes, enhanced the electrical stimulation-evoked release. At low temperature (17°C), a condition in which the transmitter uptake carriers of the plasma membrane in both the normal and reverse mode of operation are inhibited, the nicotine-evoked [3H] DA release was potentiated, whereas those evoked by amphetamine and MDMA were inhibited. At low temperature the field stimulation-evoked [3H] DA release was potentiated, but under this condition cocaine failed to increase the release. Our results show that low temperature (a) increases the concentration of extracellular DA released by Ca2+-dependent vesicular exocytosis elicited by nicotine, (b) inhibits the extracellular Ca2+-independent amphetamine- and MDMA-induced release of DA that occurs by the reverse operation of membrane carriers transporting DA from the cytoplasm of presynaptic terminals to the extraneuronal space, and (c) does not alter the inhibitory effect of cocaine on DA uptake that increases the concentration of extracellular DA released by field stimulation. The findings that the drugs of abuse tested all enhanced the release of DA in the olfactory bulb suggest that local reinforcing mechanisms may also exist in this brain area. In addition, we also show that lowering the temperature in in vitro experiments is an easy and straightforward method for separating vesicular and cytoplasmic release of transmitters, and is suitable for studying the mechanism of catecholamine release evoked by drugs of abuse. This technique may be applicable in other neurochemical studies that need inhibition of the uptake carriers without the blockade of the ligand-gated ion channels caused by reuptake inhibitor drugs.
- Dopamine release
- Low temperature
ASJC Scopus subject areas
- Cellular and Molecular Neuroscience
- Cell Biology