Differential effects of acute dopaminergic D1 and D2 receptor antagonists on proneurotensin mRNA expression in rat striatum.

The effect of acute dopamine (DA) antagonist treatment on neuronal proneurotensin (NT) mRNA was investigated in the rat striatum using a technique of non-radioactive in situ hybridisation. Adult Wistar rats were given a single intraperitoneal injection of either raclopride (D2 antagonist), SCH 23390 (D1 antagonist) or its inactive isomer SCH 23388 and left to survive for 3 h. Their brains were rapidly removed and striatal sections processed for in situ hybridisation using an alkaline phosphatase (AP) labelled oligonucleotide specific for NT mRNA. Blockade of the DA D2 receptors by a single injection of raclopride resulted in an increase in the number of NT mRNA containing cells in the dorsal lateral rim of the striatum adjacent to the corpus callosum. In contrast, no such increase was observed following blockade of the DA D1 receptors with SCH 23390. These findings demonstrate that NT mRNA expression is differentially regulated in the adult rat striatum by selective D1 and D2 antagonists.     

Determination of tryptamine in rat brain by gas chromatography-mass spectrometry

Tryptamine (TA) occurs in trace levels in the brain, but its role in the central nervous system is not clear. However, there is evidence that TA may be a neuromodulator since it binds to specific binding sites in the brain. TA was measured as a diheptafluorobutyryl derivative in rat whole brain by capillary gas chromatography—mass spectrometry using negative chemical ionization (NCI) and single ion monitoring (SIM). d₄-TA was used as the internal standard. The ions m/z 532 and m/z 536 were monitored to identify TA and d₄-TA, respectively and to calculate the concentration of TA in rat whole brain which was found to be 0.19 ± 0.08 ng g⁻¹ (n = 8). The results confirm the earlier TA concentrations measured by GC—MS using positive electron impact ionization. However, NCI improved the signal/noise ratio of the method increasing its sensitivity for TA.