Effect of acute or chronic pentobarbital administration on the steady state levels and the turnover rates of catecholamines in discrete brain areas of mice

The α2A -adrenoceptor subtype plays a key role in the analgesic and sedative effects of xylazine

Xylazine, the classical α₂ -adrenoceptor (α₂ -AR) agonist, is still used as an analgesic and sedative in veterinary medicine, despite its low potency and affinity for α₂ -ARs. Previous pharmacological studies suggested that the α_2A -AR subtype plays a role in mediating the clinical effects of xylazine; however, these studies were hampered by the poor subtype-selectivity of the antagonists used and a lack of knowledge of their bioavailability in vivo. Here, we attempted to elucidate the role of the α_2A -AR subtype in mediating the clinical effects of xylazine by comparing the analgesic and sedative effects of this drug in wild-type mice with those in α_2A -AR functional knockout mice using the hot-plate and open field tests, respectively. Hippocampal noradrenaline turnover in both mice was also measured to evaluate the contribution of α_2A -AR subtype to the inhibitory effect of xylazine on presynaptic noradrenaline release. In wild-type mice, xylazine (10 or 30 mg/kg) increased the hot-plate latency. Furthermore, xylazine (3 or 10 mg/kg) inhibited the open field locomotor activity and decreased hippocampal noradrenaline turnover. By contrast, all of these effects were abolished in α_2A -AR functional knockout mice. These results indicate that the α_2A -AR subtype is mainly responsible for the clinical effects of xylazine.

Effects of acute and chronic administrations of phencyclidine on the levels of serotonin and 5-hydroxyindoleacetic acid in discrete brain areas of mouse

The effects of phencyclidine (PCP) on the levels of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in discrete brain areas of mouse were investigated. Following a single administration, PCP significantly increased at 60 min the level of 5-HT but not 5-HIAA in the cortex. However, acute administration of PCP induced no changes of 5-HT and 5-HIAA levels in other brain areas investigated. On the other hand, chronic treatment of PCP produced a significant increase the striatal 5-HT and 5-HIAA levels by about 30% and 20%, respectively. These increased levels were gradually returned to the control levels, and there was no difference of these levels between the control group and the 48 hr withdrawal group. The changes of 5-HT level in the hypothalamus were similar to those in the striatum. These results suggest that the pharmacological actions of PCP and tolerance development to PCP may be related to the functional changes of serotonergic neuronal activity.

Catecholamine, adenosine triphosphate, and P-creatine levels in decapitated whole mouse brain

The levels of norepinephrine, epinephrine, dopamine, adenosine triphosphate, and P-creatine were measured in whole mouse brain collected under two conditions: 1) the decapitated head was immediately plunged into liquid nitrogen (nonanoxic tissue); or 2) the tissue was allowed to remain anoxic before the quick-freezing procedure. The substrate levels were significantly decreased in brain anoxic for only 30 sec. The catecholamine levels in nonanoxic mouse brain appear to be higher than levels previously reported in brains collected with microwave irradiation or by decapitation with rapid dissection of tissue before it was frozen.