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PubMed2003

An immunohistochemical study of the thyroid parafollicular (C) cells in rats treated with cannabinoids - preliminary investigations.

The purpose of the present study was to evaluate the effect of a single intraperitoneal injection of a stable analogue of endogenous cannabinoid anandamide - R-(+)-methanandamide (2.5 mg/kg) and CP 55,940 (0.25 mg/kg), an egzogenous CB1 receptor-agonist, on the calcitonin (CT) immunoreactivity of the thyroid parafollicular (C) cells. Four hours after injection with both cannabinoids CT immunoreactivity, evaluated with an avidin-biotin peroxidase complex method by means of rabbit antibodies against CT, was seen to be enhanced in the parafollicular cells in comparison to those of the control group. In thyroids taken from cannabinoid-treated rats the majority of follicles, particularly those located peripherally were large in size, and had low epithelium. Moreover, dilatation of the blood vessels was observed. These changes were accompanied by a significant decrease in CT plasma level, without changes in calcium concentrations. This is the first evidence that a single injection of the cannabinoids R-(+)-methanandamide and CP 55,940 significantly decreases the activity of thyroid C cells.

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PubMedDate not supplied

Cannabinoids alter recognition memory in rats.

Cannabinoids are known to attenuate learning and memory in both humans and animals. In rodents, disruptive effect of cannabinoids on memory, reversed by SR 141716, a specific CB(1) receptor antagonist, was shown in behavioral tests based on conditioning. There are no data concerning the influence of cannabinoids on recognition memory. Recently, the improvement of recognition memory in cannabinoid CB(1) receptor knock-out mice was reported. Therefore, the purpose of the present study was to determine whether a stable analogue of endogenous cannabinoid anandamide, R-(+)-methanandamide (0.25 and 2.5 mg/kg, i.p.) and a potent CB(1) receptor agonist, CP 55,940 (0.025 and 0.25 mg/kg i.p.) affect recognition memory in rats evaluated in an object recognition test, based on discrimination between the familiar and a new object presented at 1h interval. Because cannabinoids at the higher doses can produce motor inhibition, the influence of both compounds on psychomotor activity was evaluated in an open field test. CP 55,940 and R-(+)-methanandamide, at both doses given once, 15 min before the learning trial, significantly attenuated recognition memory, measured by the difference in exploration of a new object and a duplicate of the familiar object. Moreover, CP 55,940 at the higher dose significantly attenuated ambulation, and bar approaches, and at both doses also rearings, evaluated in an open field, performed immediately after an object recognition test, while R-(+)-methanandamide at both doses did not alter locomotor and exploratory activity of rats. This is the first evidence that cannabinoids impair recognition memory in rats.

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