Phenothiazine-type Antipsychotics Elicit Cutaneous Analgesia in Rats

Effect of novel phenothiazine derivatives on brain dopamine in Wistar rats

Background

Neurotransmitters are involved in several functions in the brain and the body of living things. Changes in the level of neurotransmitters in the brain are associated with several illnesses. Some of the drugs are controlling the neurotransmitter by adjusting the level in the brain and are exclusively used in the treatment of psychological disorders. The purpose of the study was to find out the effect of novel synthesised phenothiazine derivatives (GC1, GC2 and GC8) either alone (7.5 mg/kg or 15 mg/kg, oral) or in combination with amphetamine on the experimental animals.

Results

Dopamine level in rat brain was estimated by a spectroscopic method using the UV-visible double beam spectrophotometer at 735 nm. The results revealed that these derivatives blocked the brain dopamine level significantly. The compound GC8 (15 mg/kg) significantly reduced the level of dopamine (0.151 ± 0.04, 0.284 ± 0.03) as similar to that of a standard drug. Furthermore, compounds GC2 (15 mg/kg) and GC1 (15 mg/kg) exhibited a varying level of dopamine inhibition level and have been found at 0.203 ± 0.06 μg/ml, 0.302 ± 0.04 μg/ml, 0.234 ± 0.02 μg/ml and 0.318 ± 0.07 μg/ml, respectively, after the administration of these derivatives either alone or in combination with amphetamine.

Conclusions

The study revealed that the compound 2-amino-6-(3-hydroxy-4-methyl phenyl) pyrimidine-4-yl) (7-chloro-10-(3- (N, N-dimethylamino) propyl)-10H-phenothiazine-3-yl) methanone (GC8, 15 mg/kg) extensively reduced the dopamine level. The order of dopamine-inhibiting effect of the selected compound was found to be GC8 > GC2 > GC1. The increased body weight and relative brain-body weight were also observed in the tested animals due to more intake of food and fluid retention.

Graphical abstract

Promazine and chlorpromazine for prolonged spinal anesthesia in rats

Though promazine and chlorpromazine elicited cutaneous anesthesia, no study of spinal anesthesia with chlorpromazine and promazine has been reported. This study was to examine whether chlorpromazine and promazine produce spinal anesthesia. Using a rat model via intrathecal injection, we tested spinal blockades of motor function and nociception by promazine, chlorpromazine or bupivacaine, and so were dose-response studies and durations. We demonstrated that chlorpromazine and promazine elicited dose-dependent spinal blockades in motor function and nociception. On the 50% effective dose (ED(50)) basis, the rank of potency of these drugs was bupivacaine>promazine>chlorpromazine (P<0.05 for the differences). On an equipotent basis (25% effective dose [ED(25)], ED(50), and ED(75)), the block duration caused by chlorpromazine or promazine was longer than that caused by the long-lasting local anesthetic bupivacaine (P<0.01 for the differences). Chlorpromazine and promazine, as well as bupivacaine, showed longer duration of sensory block than that of motor block. Our data reported that intrathecal promazine and chlorpromazine with a more sensory-selective action over motor blockade had less potent and longer-lasting spinal blockades when compared with bupivacaine.

The role of antipsychotics in the management of fibromyalgia

Fibromyalgia is a syndrome characterized by chronic generalized pain associated with different somatic symptoms, such as sleep disturbances, fatigue, stiffness, balance problems, hypersensitivity to physical and psychological environmental stimuli, depression and anxiety. It has been estimated to affect roughly the 2-4% of the general population in most countries studied, and it has been shown to be much more prevalent in women than in men. Although its pathophysiology is not yet fully understood, it is known that both genetic and environmental factors are involved in its development. Fibromyalgia shares a high degree of co-morbidity with other conditions, including chronic headache, temporomandibular disorder, irritable bowel syndrome, major depression, anxiety disorders and chronic fatigue syndrome. Therefore, this is a syndrome difficult to treat for which multimodal treatments including physical exercise, psychological therapies and pharmacological treatment are recommended. Although different kinds of drugs have been studied for the treatment of fibromyalgia, the most widely used drugs that have the higher degree of evidence for efficacy include the α(2)δ ligands pregabalin and gabapentin, and the tricyclic antidepressants (TCAs) and serotonin noradrenaline (norepinephrine) reuptake inhibitors (SNRIs). However, there is a need to look for newer additional therapeutic pharmacological options for the treatment of this complex and disabling disease. First- and second-generation antipsychotics have shown analgesic properties both in an experimental setting and in humans, although most of the available evidence for the treatment of human pain concerns older antipsychotics and involves clinical trials performed several decades ago. In addition, several second-generation antipsychotics, risperidone, olanzapine and quetiapine, have shown efficacy in the treatment of some anxiety disorders. Some second-generation antipsychotics, mainly quetiapine, aripiprazole and amisulpride, have demonstrated antidepressant activity, with quetiapine approved for the treatment of bipolar depression and refractory major depression, and aripiprazole approved as an adjunctive treatment for major depressive disorder. Finally, several old and new antipsychotics, including promethazine, levopromazine, olanzapine, quetiapine and ziprasidone, have been shown to improve sleep parameters in healthy subjects. Each of these properties suggests that antipsychotics could represent a new potential alternative for the treatment of fibromyalgia syndrome. To date, most of the published studies on the use of antipsychotics in the treatment of fibromyalgia syndrome have been uncontrolled, either case reports or case series, dealing with olanzapine, quetiapine, ziprasidone, levopromazine and amisulpride. The studies on olanzapine and quetiapine have suggested therapeutic efficacy although, in the case of olanzapine, hampered by tolerability problems. A double-blind controlled trial, published in 1980, showed that chlorpromazine increased slow-wave sleep and improved pain and mood disturbances. More recently, four double-blind controlled studies have explored the efficacy of quetiapine, either alone or as an add-on treatment, in fibromyalgia management. None of these trials has yet been published, although two of them have been presented as congress communications, both of them suggesting that quetiapine could be a potential alternative treatment for fibromyalgia. In summary, the current available evidence suggests that at least some antipsychotics, specifically quetiapine, could be useful for the treatment of fibromyalgia and that further studies on the efficacy of these compounds are worth pursuing.