Effects of acute and long-term treatments with thyrotropin-releasing hormone on locomotor activity and jumping behavior in mice

The effects of amphetamine injections on feeding behavior and the brain expression of orexin, CART, tyrosine hydroxylase (TH) and thyrotropin releasing hormone (TRH) in goldfish (Carassius auratus)

In this study, the effects of peripheral (intraperitoneal) injections of D-amphetamine on feeding behavior were assessed in goldfish. Compared with the saline-injected group, amphetamine injections decreased food intake at doses ranging from 1 to 75 μg/g, but not 0.5 μg/g, but increased locomotor behavior, as indicated by the increased number of total feeding and non-feeding acts, at doses ranging from 2.5 to 25 μg/g. Amphetamine at high doses inhibited both food intake (at 25, 50 and 75 μg/g) and feeding behavior (at 75 μg/g). In the hypothalamus, the expression of orexin was down-regulated, and both CART 1 and CART 2 expressions were up-regulated in amphetamine-treated fish (50 μg/g) as compared to saline-injected fish, but amphetamine treatment had no effect on either hypothalamic TH or TRH expression. In the telencephalon, amphetamine treatment (50 μg/g) up-regulated CART 1, CART 2 and TH mRNA expressions but had no effect on either orexin or TRH. Our results suggest that, as in mammals, the orexin, CART and TH systems might be involved in amphetamine-induced feeding/locomotor responses in goldfish.

Thyrotropin Releasing Hormone (TRH) in goldfish (Carassius auratus): role in the regulation of feeding and locomotor behaviors and interactions with the orexin system and cocaine- and amphetamine regulated transcript (CART)

TRH is a peptide produced by the hypothalamus which major function in mammals is the regulation of TSH secretion by the pituitary. In fish, TRH does not appear to affect TSH secretion, suggesting that it might regulate other functions. In this study, we assessed the effects of central (intracerebroventricular, icv) injections of TRH on feeding and locomotor behavior in goldfish. TRH at 10 and 100 ng/g, but not 1 ng/g, significantly increased feeding and locomotor behaviors, as indicated by an increase in food intake and in the number of total feeding acts as compared to saline-injected fish. In order to assess possible interactions between TRH and other appetite regulators, we examined the effects of icv injections of TRH on the hypothalamic expression of orexin, orexin receptor and CART. The mRNA expression levels of all three peptides were significantly increased in fish injected with TRH at 100 ng/g as compared to saline-injected fish. Fasting increased TRH, orexin, and orexin receptor hypothalamic mRNA levels and decreased CART hypothalamic mRNA levels. Our results suggest that TRH is involved in the regulation of feeding/locomotor activity in goldfish and that this action is associated with a stimulation of both the orexin and CART systems.

Mice lacking leukocyte common antigen-related (LAR) protein tyrosine phosphatase domains demonstrate spatial learning impairment in the two-trial water maze and hyperactivity in multiple behavioural tests

Leukocyte common antigen-related (LAR) protein is a cell adhesion molecule-like receptor-type protein tyrosine phosphatase. We previously reported that in LAR tyrosine phosphatase-deficient (LAR-Delta P) mice the number and size of basal forebrain cholinergic neurons as well as their innervation of the hippocampal area was reduced. With the hippocampus being implicated in behavioural activity aspects, including learning and memory processes, we assessed possible phenotypic consequences of LAR phosphatase deficiency using a battery of rodent behaviour tests. Motor function and co-ordination tests as well as spatial learning ability assays did not reveal any performance differences between wildtype and LAR-Delta P mice. A spatial learning impairment was found in the difficult variant of the Morris water maze. Exploration, nestbuilding and activity tests indicated that LAR-Delta P mice were more active than wildtype littermates. The observed hyperactivity in LAR-Delta P mice could not be explained by altered anxiety or curiosity levels, and was found to be persistent throughout the nocturnal period. In conclusion, behavioural testing of the LAR-Delta P mice revealed a spatial learning impairment and a significant increase in activity.

Effect of thyrotropin-releasing hormone on the locomotor and sensitizing effects of cocaine in rats

The present study was designed to find out whether single and repeated treatment with thyrotropin-releasing hormone (TRH) changed the cocaine-evoked hyperactivation or sensitization, and whether cross-sensitization occurred between TRH and cocaine. Like cocaine (10 mg/kg), TRH (10 mg/kg) increased the basal activation of rats; however, when given in combination with cocaine (10 mg/kg), TRH (5-10 mg/kg) did not change the locomotor effect of cocaine. On day 10, cocaine challenge of rats treated repeatedly with the psychostimulant (days 1-5) significantly enhanced locomotor hyperactivity compared to the effect of acute cocaine injection in saline-treated (days 1-5) animals. When co-administered with cocaine for 5 days during the development of sensitization, TRH (10 mg/kg) enhanced the effect of the challenge dose of cocaine (10 mg/kg) following a 5-day withdrawal. Given acutely with cocaine on day 10 to cocaine-treated animals, TRH (5-10 mg/kg) did not change the expression of cocaine sensitization. Significant enhancement of the locomotor response to TRH (10 mg/kg) challenge was observed in animals treated repeatedly with TRH. The response to TRH (5-10 mg/kg) was stronger in repeated cocaine-treated rats than in saline-injected ones; similarly, the response to cocaine (10 mg/kg) was more potent in TRH-treated animals compared to saline-injected ones (cross-sensitization). In conclusion, our results indicate that exposure to TRH induces sensitization to its locomotor hyperactivity effect. They also show that TRH enhances the development of cocaine sensitization, but affects neither the expression phase of the phenomenon nor the locomotor hyperactivity induced by a single dose of cocaine. Moreover, cross-sensitization between cocaine and TRH has also been demonstrated. These findings also may provide an insight into the relationship between TRH and cocaine in humans exposed to the psychostimulant.