F. Rodríguez de Fonseca

Dopamine activation of endogenous cannabinoid signaling in dorsal striatum

We measured endogenous cannabinoid release in dorsal striatum of freely moving rats by microdialysis and gas chromatography/mass spectrometry. Neural activity stimulated the release of anandamide, but not of other endogenous cannabinoids such as 2-arachidonylglycerol. Moreover, anandamide release was increased eightfold over baseline after local administration of the D2-like (D2, D3, D4) dopamine receptor agonist quinpirole, a response that was prevented by the D2-like receptor antagonist raclopride. Administration of the D1-like (D1, D5) receptor agonist SKF38393 had no such effect. These results suggest that functional interactions between endocannabinoid and dopaminergic systems may contribute to striatal signaling. In agreement with this hypothesis, pretreatment with the cannabinoid antagonist SR141716A enhanced the stimulation of motor behavior elicited by systemic administration of quinpirole. The endocannabinoid system therefore may act as an inhibitory feedback mechanism countering dopamine-induced facilitation of motor activity.

An anorexic lipid mediator regulated by feeding

Oleylethanolamide (OEA) is a natural analogue of the endogenous cannabinoid anandamide. Like anandamide, OEA is produced in cells in a stimulus-dependent manner and is rapidly eliminated by enzymatic hydrolysis, suggesting a function in cellular signalling. However, OEA does not activate cannabinoid receptors and its biological functions are still unknown. Here we show that, in rats, food deprivation markedly reduces OEA biosynthesis in the small intestine. Administration of OEA causes a potent and persistent decrease in food intake and gain in body mass. This anorexic effect is behaviourally selective and is associated with the discrete activation of brain regions (the paraventricular hypothalamic nucleus and the nucleus of the solitary tract) involved in the control of satiety. OEA does not affect food intake when injected into the brain ventricles, and its anorexic actions are prevented when peripheral sensory fibres are removed by treatment with capsaicin. These results indicate that OEA is a lipid mediator involved in the peripheral regulation of feeding.

Downregulation of rat brain cannabinoid binding sites after chronic Δ9-tetrahydrocannabinol treatment

Specific cannabinoid receptors have been recently described in extrapyramidal and limbic areas and presumably might mediate the effects of marijuana exposure on behavioral processes related to those areas. In this work, we examined whether cannabinoid receptors exhibit downregulation as a consequence of the chronic exposure to delta 9-tetrahydrocannabinol (THC), which might explain certain tolerance phenomena observed in relation to motor and limbic effects of marijuana. To this end, we first characterized the binding of cannabinoid receptors, by using [3H]CP-55,940 binding assays, in the striatum, limbic forebrain, and ventral mesencephalon of male rats, and, second, we measured the density and affinity of those receptors in these brain areas after 7 days of a daily treatment with THC. Development of a tolerance phenomenon was behaviorally tested by using an open-field technique. Results were as follows. The three areas studies presented specific and saturable binding for the cannabinoid ligand, as revealed by their corresponding association and dissociation curves, displacement by THC, saturation curves, and Scatchard plots. A chronic treatment with THC produced the expected tolerance phenomenon: The decrease caused by an acute dose in spontaneous locomotor (49.4%) and exploratory (59.7%) activities and, mainly, the increase in the time spent by the rat in inactivity (181.7%) were diminished after 7 days of daily treatment (39.4, 40.4, and 31.7%, respectively). This tolerance was accompanied by significant decreases in the density of cannabinoid receptors in the striatum and limbic forebrain, the areas where nerve terminals for nigrostriatal and mesolimbic dopaminergic systems, respectively, which play an important role in those processes, are located.(ABSTRACT TRUNCATED AT 250 WORDS)

Cannabinoid receptors in rat brain areas: Sexual differences, fluctuations during estrous cycle and changes after gonadectomy and sex steroid replacement

Cannabinoid effects on brain dopaminergic activity vary as a function of gonadal status. In this work, we examined whether these variations might be due to sex steroid-dependent differences in brain cannabinoid receptors (CNr). Four experiments were done: (i) male versus females; (ii) females at each stage of the ovarian cycle; (iii) estradiol (E2) and/or progesterone (P)-replaced ovariectomized (OVX) females; and (iv) testosterone (T)-replaced orchidectomized males. The density of CNr in the medial basal hypothalamus fluctuated in females during the estrous cycle. The density was higher in diestrus and decreased in estrus. This parameter did not change after ovariectomy and E2 replacement. However, P increased the density of CNr when administered to OVX rats acutely treated with E2, but not administered alone or after chronic E2 treatment. In the striatum, the affinity of CNr was slightly higher in males than females, with no changes in density. Ovariectomy increased the affinity of CNr, which normalized only after administration of acute E2. Interestingly, the high affinity values observed in this area after P alone or combined with E2, corresponded to low densities as compared with intact females. In the limbic forebrain, the affinity for the cannabinoid ligand was also higher in males than females with no changes in density. Affinity was also higher in diestrus and lower in estrus, whereas density was unchanged. Ovariectomy decreased CNr density. A normal situation was found after administration of acute E2 or P alone, whereas chronic E2 markedly increased the density of CNr as compared with both intact and OVX females. Interestingly, this latter increase was prevented by coadministration of P. Orchidectomy did not affect CNr density, but administration of T produced a marked decrease. In the mesencephalon, the density and affinity of CNr was higher in males than females. Administration of P to OVX rats produced opposite effects, increasing the density when administered alone and decreasing it when administered to acute E2-replaced OVX rats. In summary, these results reveal the existence of subtle, sometimes more pronounced, sex dimorphisms, fluctuations along the ovarian cycle and changes after gonadectomy and sex steroid replacement in CNr density and affinity in certain brain areas. This supports the hypothesis of possible sex steroid-dependent differences in the sensitivity of certain neuronal processes to cannabinoid treatment.

Neuroanatomical relationship between type 1 cannabinoid receptors and dopaminergic systems in the rat basal ganglia

Dopamine and endocannabinoids are neurotransmitters known to play a role in the activity of the basal ganglia motor circuit. While a number of studies have demonstrated functional interactions between type 1 cannabinoid (CB1) receptors and dopaminergic systems, we still lack detailed neuroanatomical evidence to explain their relationship. Single- and double-labeling methods (in situ hybridization and immunohistochemistry) were employed to determine both the expression and localization of CB1 receptors and tyrosine hydroxylase (TH) in the basal ganglia. In the striatum, we found an intense signal for CB1 receptor transcripts but low signal for CB1 receptor protein, whereas in the globus pallidus and substantia nigra we found the opposite; no hybridization signal but intense immunoreactivity. Consequently, CB1 receptors are synthesized in the striatum and mostly transported to its target areas. No co-expression or co-localization of CB1 receptors and TH was found. In the caudate-putamen, globus pallidus and substantia nigra, TH-immunoreactive fibers were interwoven with the CB1 receptor-immunoreactive neuropil and fibers. Our data suggest that the majority of the striatal CB1 receptors are located presynaptically on inhibitory GABAergic terminals, in a position to modulate neurotransmitter release and influence the activity of substantia nigra dopaminergic neurons. In turn, afferent dopaminergic fibers from the substantia nigra innervate CB1 receptor-expressing striatal neurons that are known to also express dopamine receptors. In conclusion, these data provide a neuroanatomical basis to explain functional interactions between endocannabinoid and dopaminergic systems in the basal ganglia.

The endocannabinoid system, eating behavior and energy homeostasis: the end or a new beginning?

The endocannabinoid system (ECS) consists of two receptors (CB(1) and CB(2)), several endogenous ligands (primarily anandamide and 2-AG), and over a dozen ligand-metabolizing enzymes. The ECS regulates many aspects of embryological development and homeostasis, including neuroprotection and neural plasticity, immunity and inflammation, apoptosis and carcinogenesis, pain and emotional memory, and the focus of this review: hunger, feeding, and metabolism. This mini-review summarizes the main findings that supported the clinical use of CB1 antagonists/inverse agonists, the clinical concerns that have emerged, and the possible future of cannabinoid-based therapy of obesity and related diseases. The ECS controls energy balance and lipid metabolism centrally (in the hypothalamus and mesolimbic pathways) and peripherally (in adipocytes, liver, skeletal muscle and pancreatic islet cells), acting through numerous anorexigenic and orexigenic pathways. Obese people seem to display an increased endocannabinoid tone, driving CB(1) receptor in a feed-forward dysfunction. Several CB(1) antagonists/inverse agonists have been developed for the treatment of obesity. Although these drugs were found to be efficacious at reducing food intake as well as abdominal adiposity and cardiometabolic risk factors, they resulted in adverse psychiatric effects that limited their use and finally led to the end of the clinical use of systemic CB(1) ligands with significant inverse agonist activity for complicated obesity. However, the existence of alternatives such as CB(1) partial agonists, neutral antagonists, antagonists restricted to the periphery, allosteric modulators and other potential targets within the ECS indicate that a cannabinoid-based therapy for the management of obesity and its associated cardiometabolic sequelae should remain open for consideration.

Effects of pre- and perinatal exposure to hashish extracts on the ontogeny of brain dopaminergic neurons

The changes induced by maternal exposure to cannabinoids in the maturation of nigrostriatal, tuberoinfundibular and mesolimbic dopaminergic activities of rat offspring 15-40 days old were studied. In the striatum, tyrosine hydroxylase activity was constantly decreased during cannabinoid exposure in males. This decrease was correlative to increased number of D1 and D2 dopaminergic receptors. Both effects were also observed after the drug withdrawal caused by weaning on day 24. In females, the most consistent effect appeared on day 20, when decreased dopamine content and number of D1 receptors were observed. Both effects disappeared after drug withdrawal, but the reduction in the number of D1 receptors was again observed 40 days after birth. In the limbic area, cannabinoid exposure caused a decrease in the number of D1 receptors in 15-day-old females, along with decreases in the content of dopamine and its metabolite, L-3,4-dihydroxyphenylacetic acid. Changes in receptors disappeared on subsequent days, but increases in L-3,4-dihydroxyphenylacetic acid content and in its ratio with dopamine (L-3,4-dihydroxyphenylacetic acid/dopamine) were observed on day 20 followed by a decrease in the neurotransmitter content on day 30. In males, tyrosine hydroxylase activity increased on day 30, followed by an increase in L-3,4-dihydroxyphenylacetic acid content and L-3,4-dihydroxyphenylacetic acid/dopamine ratio on day 40. In the hypothalamus, the cannabinoid effects were always manifested after the cessation of drug exposure. Thus, a rise in L-3,4-dihydroxyphenylacetic acid/dopamine ratio was observed in 30-day-old females, and it was followed by a decrease on day 40, accompanied by a decrease in the anterior pituitary content of dopamine. Rise in prolactin release was not significant. In males, tyrosine hydroxylase activity was increased 30 days after birth, while L-3,4-dihydroxyphenylacetic acid content decreased. On day 40, L-3,4-dihydroxyphenylacetic acid content increased, paired to a rise in L-3,4-dihydroxyphenylacetic acid/dopamine ratio and anterior pituitary content of dopamine and to a decrease in the prolactin release. Perinatal exposure to cannabinoids altered the normal development of nigrostriatal, mesolimbic and tuberoinfundibular dopaminergic neurons, as reflected by changes in several indices of their activity. These changes were different regarding the sex and brain areas. Cannabinoid effects were more marked and constant in the striatum of males, while alterations in limbic neurons were mostly transient and those in hypothalamic neurons occurred after drug withdrawal. A long-term impact of these early changes on the neurological processes of adulthood is plausible.

Motor behavior and nigrostriatal dopaminergic activity in adult rats perinatally exposed to cannabinoids

We have recently reported several neurochemical alterations, measured at perinatal and peripubertal ages, in the maturation of nigrostriatal dopaminergic neurons following perinatal hashish exposure. In the present work, we tried to undertake whether these neurochemical changes during ontogeny: a) were accompanied by changes of motor behavior, the main neurobiological process regulated by nigrostriatal dopaminergic neurons; and b) persisted in adulthood, leading to disturbances in the expression of an adult motor activity. To this end, two different experiments were performed. In the first, we examined, by using an actimeter, the ontogeny of spontaneous locomotor activity in immature male and female rats born from mothers perinatally exposed to hashish extract. Results showed a complete absence of significant changes in locomotor activity in females, whereas males presented a constant trend to decrease, although never statistically significant, at all ages studied as a consequence of the perinatal cannabinoid exposure. In the second experiment, we evaluated neurochemical indices--dopamine (DA) and L-3,4-dihydroxyphenylacetic acid (DOPAC) contents, tyrosine hydroxylase (TH) activity, and number and affinity of D1 and D2 dopaminergic receptors in the striatum--and behavioral parameters--spontaneous locomotor activity and spontaneous and induced stereotypic behavior--both indicating nigrostriatal dopaminergic activity, in adult female and male rats perinatally exposed to hashish extract. Results were as follows. The spontaneous locomotor activity, measured in the actimeter, was not affected by perinatal hashish exposure in both adult males and females. This was also seen in an open-field test as measured by total number of sector crossings. However, when differentiated between internal and external sectors hashish-exposed males presented a higher number of external crossings than controls, which did not appear in females. Moreover, several induced stereotypic behaviors, such as self-grooming and shaking induced by water spraying, were also altered by hashish treatment in a sexually dimorphic manner, whereas the number of spontaneous rears and self-grooms, measured in the open-field test, was unchanged. Thus, the frequency of water spraying-induced self-grooming was significantly increased in both males and females perinatally exposed to hashish, although the increase was more marked in males (200.4%) than females (121.2%). In addition, the frequency of shaking was also markedly increased in males but remained unchanged in females. These behavioral effects were paralleled by modifications in striatal neurochemical parameters. Thus, there was a significant increase in the DOPAC/DA ratio, indicating increased presynaptic activity, in females perinatally exposed to hashish, but compensated by a lower density of D1 receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

Sex-dependent alterations in response to maternal deprivation in rats

We review here our latest results regarding short- and long-term effects of a neonatal maternal deprivation (MD) stress [24h at postnatal day (PND) 9] on diverse psychoneuroimmunoendocrine parameters, pointing out the existence of numerous sexual dimorphisms. Behavioral changes observed in MD animals might be at least in part attributable to neurodevelopmental effects of MD-induced elevated corticosterone levels. Our findings of short-term effects of MD on hippocampal and cerebellar neurons and glial cells appear to support this hypothesis. However, it is important to note that these cellular effects were more marked in males than in females. Moreover, in analyzing the effects of this neonatal stress on the endocannabinoid system (hippocampal endocannabinoid levels and CB1 receptors) we have also found that males were more affected by MD. Since all these sexual dimorphisms were found at an early neonatal age (PND 13), they are attributable to organizational effects of gonadal steroids. We discuss the potential implications of the elevated corticosterone and decreased leptin levels shown by MD animals in their diverse functional alterations, including the above mentioned neural effects as well as the intriguing persistent deficit in their immunological system. We also emphasize the necessity of analyzing the important influence of sex as regards the specific consequences of early life stress.

Acute effects of δ-9-tetrahydrocannabinol on dopaminergic activity in several rat brain areas

Abstract In this work, we examined the acute effects of two doses of δ-9-tetrahydrocannabinol (THC) on several pre- and postsynaptic biochemical measures of dopaminergic activity in the striatum, limbic forebrain, and hypothalamic-anterior pituitary area of adult male rats. The exposure to a low dose of THC (0.5 mg/kg bw) decreased the number of striatal D 2 dopaminergic binding sites, but did not affect their affinity. Treatment with a higher dose of THC was ineffective. In addition, both doses decreased the number of D 1 dopaminergic binding sites in the limbic forebrain without changing their affinity. We did not find any changes in the dopamine (DA) or L -3,4-dihydroxyphenylacetic acid (DOPAC) content, or in the DOPAC/DA ratio, in either the striatum or limbic forebrain. THC treatment produced a dose-related decline in plasma prolactin (PRL) levels. Furthermore, both the basal and DA-inhibited in vitro release were PRL were reduced in animals exposed to THC in a dose-dependent manner. This inhibitory effect of THC on PRL release was accompanied by a decreased DOPAC/DA ratio in the medial basal hypothalamus that, in turn, may be a result of the fall in PRL levels rather than a direct action of the drug. These data show that acute exposure to THC can alter brain dopaminergic neurotransmission. Our results suggest that the reduction of PRL release following THC exposure, both in vivo and in vitro, might be elicited by a direct action of THC on the pituitary.