A CB2 receptor agonist,A-836339, modulates wide dynamic range neuronal activity in neuropathic rats: Contributions of spinal and peripheral CB2 receptors

We investigated the systemic and site-specific actions of a selective CB₂ receptor agonist, A-836339 on mechanically evoked (10 g von Frey hair) and spontaneous firing of spinal wide dynamic range (WDR) neurons in neuropathic (L5 and L6 ligations) and sham rats. Systemic administration of A-836339 (0.3–3 μmol/kg, i.v.) reduced both evoked and spontaneous WDR neuronal activity in neuropathic, but not sham rats. The effects in neuropathic rats were blocked by pre-administration of a CB₂, but not a CB₁, receptor antagonist. Similar to systemic delivery, intra-spinal injection of A-836339 (0.3 and 1 nmol) also attenuated both von Frey–evoked and spontaneous firing of WDR neurons in neuropathic rats. Intra-spinal injections of A-836339 were ineffective in sham rats. Application of A-836339 (3–30 nmol) onto the ipsilateral L5 dorsal root ganglion (DRG) of neuropathic rats reduced the von Frey–evoked activity of WDR neurons, but spontaneous firing was unaltered. All effects of A-836339 on WDR neuronal activity following either intra-spinal or intra-DRG administration were blocked by pre-administration of a CB₂ receptor antagonist. Pre-administration of a CB₁ receptor antagonist did not alter the site-specific effects of A-836339. Injection of A-836339 (300 nmol) into the neuronal receptive field on the ipsilateral hind paw did not affect evoked or spontaneous firing of WDR neurons. Thus, the current data demonstrate that modulation of spinal neuronal activity by a CB₂ receptor agonist is enhanced following peripheral nerve injury, and further delineate the contribution of spinal and peripheral CB₂ receptors to this modulation.     

Precipitated withdrawal counters the adverse effects of subchronic cannabinoid administration on male rat sexual behavior

In the present study, sexual behavior of male rats was assessed following prolonged treatment with the CB₁ receptor agonist, HU-210 (0.1 mg/mg/day for 10 days) under conditions of drug maintenance, spontaneous withdrawal and precipitated withdrawal (induced via administration of the CB₁ receptor antagonist AM251; 1 mg/kg). Following subchronic cannabinoid treatment, sexual activity in male rats was impaired under both the drug maintenance and spontaneous withdrawal conditions, as revealed by a reduction in frequency of both intromissions and ejaculations. Notably, the induction of precipitated drug withdrawal reversed the negative effects of subchronic HU-210 treatment on sexual activity as seen by a reversal of the suppression of ejaculations. These data illustrate that, contrary to expectations, the impairments in male sexual activity following protracted cannabinoid administration are not due to drug withdrawal, per se, but are likely mediated by neuroadaptive changes provoked by repeated drug exposure.     

The cannabinoid agonist WIN55212-2 decreases L-DOPA-induced PKA activation and dyskinetic behavior in 6-OHDA-treated rats

Chronic Levodopa (l-DOPA), the gold standard therapy for Parkinson's disease (PD), causes disabling motor complications (dyskinesias) that are associated with changes in the activity of striatal protein kinase A (PKA) and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32). In this study, we showed that systemic administration of the cannabinoid agonist WIN55212-2 ameliorated l-DOPA-induced abnormal involuntary movements (AIMs) in the 6-OHDA rat model of PD and reversed l-DOPA-induced PKA hyperactivity via a CB₁-mediated mechanism. This effect was accompanied by increased phosphorylation of DARPP-32 at threonine 34, which was partially blocked by CB₁ antagonism. Striatal PKA activity was positively correlated with the severity of l-DOPA-induced axial and limb dyskinesias, suggesting a role for the cAMP/PKA signaling pathway in the expression of these motor disturbances.Our results indicate that activation of CB₁ receptors, as well as reduction of striatal PKA hyperactivity, might be an effective strategy for the treatment of l-DOPA-induced dyskinesias.     

CRIP1a switches cannabinoid receptor agonist/antagonist-mediated protection from glutamate excitotoxicity

A shared pathology among many neurological and neurodegenerative disorders is neuronal loss. Cannabinoids have been shown to be neuroprotective in multiple systems. However, both agonists and antagonists of the CB₁ cannabinoid receptor are neuroprotective, but the mechanisms responsible for these actions remain unclear. Recently a CB₁ receptor interacting protein, CRIP1a, was identified and found to alter CB₁ activity. Here we show that in an assay of glutamate neurotoxicity in primary neuronal cortical cultures CRIP1a disrupts agonist-induced neuroprotection and confers antagonist-induced neuroprotection.     

Intraganglionic laminar endings in the rat esophagus contain purinergic P2X2 and P2X3 receptor immunoreactivity

Intraganglionic laminar endings (IGLEs) represent the most prominent vagal afferent terminal structures throughout the gastrointestinal tract. They are most prominent in the esophagus and stomach, but can be found down to the distal colon. Their role as mechanosensors as proposed on anatomical grounds was recently substantiated in elegant functional experiments. There is evidence that vagal mechanosensors in the esophagus and stomach respond to ATP. Thus, the present study aimed at detecting purinergic receptors on IGLEs. IGLEs in the rat esophagus were identified by immunohistochemistry for calretinin and sections were co-incubated with antibodies directed against P2X₂ or P2X₃ receptors. Also, double label immunocytochemistry for purinergic receptors and calcitonin gene-related peptide as a marker for spinal afferents was performed. Terminal nerve fibers immunoreactive for P2X₂ and P2X₃, respectively, were observed between outer and inner layers of the tunica muscularis, covering myenteric ganglia totally or partly. Both P2X₂ and P2X₃ receptor immunoreactivities were highly co-localized with calretinin positive IGLEs as shown by confocal laser scanning microscopy. Numerous calcitonin gene-related peptide immunostained fibers were found to closely approach and intermingle with P2X immunopositive IGLEs. However, there was never co-staining for either of the purinergic receptors and calcitonin gene-related peptide within the same fibers. P2X₃ but not P2X₂ immunoreactivity was also observed within nerve fiber arborizations in the mucosa of the pharynx. In the nodose ganglion, 8.9±1.1% of P2X₂ and 7.2±1.3% of P2X₃ immunopositive neurons, respectively, co-stained for calretinin. On the other hand, 63.4±4.6% and 60.1±5.3% of calretinin positive cell bodies contained P2X₂ and P2X₃ receptor immunoreactivity, respectively. These results indicate that IGLEs are equipped with both P2X₂ and P2X₃ receptors. Thus, they may act as chemosensors or their mechanosensory properties may be modulated by ATP. It is also suggested that spinal afferents innervating the esophagus are equipped with neither P2X₂ nor P2X₃ purinergic receptors.     

Cannabinoid CB2-Selective Inverse Agonist Protects Against Antigen-Induced Bone Loss

Work to improve the therapeutic properties of cannabinoid CB₂ receptor-selective inverse agonists has led to the development of Sch.036, an aryl substituted triaryl bis-sulfone with improved oral pharmacokinetic parameters. In this report, we show that this compound blocks in vivo trafficking of various leukocyte populations, a property consistent with other members of this chemical series. This CB₂-selective compound also shows efficacy in leukocyte recruitment models when added in concert with suboptimal doses of selected anti-inflammatory agents, consistent with its unique function and indicative of its potential therapeutic utility. Finally, studies with Sch.036 show that this cannabinoid CB₂-specific inverse agonist can ameliorate bone damage in a rat model of relapsing-remitting arthritis. This result suggests that a cannabinoid CB₂‐selective inverse agonist may help ameliorate a particularly harmful property of this inflammatory joint disease.     

Involvement of enkephalins in the inhibition of osteosarcoma-induced thermal hyperalgesia evoked by the blockade of peripheral P2X3 receptors

Although previous studies describe the up-regulation of purinergic P2X₃ receptors expressed at peripheral nociceptive fibers in experimental painful neoplastic processes, the analgesic efficacy of P2X₃ receptor antagonists has not been tested in these settings. We study here the effect of the P2X₃ receptor antagonist, A-317491, on thermal hyperalgesia produced by the intratibial inoculation of NCTC 2472 fibrosarcoma cells to C3H/HeJ mice. The peritumoral administration of A-317491 (10–100 μg) dose-dependently attenuated osteosarcoma-induced thermal hyperalgesia without modifying thermal latencies measured in the contralateral paws. This antihyperalgesic effect was inhibited by the coadministration of naloxone-methiodide (0.1–1 μg) or the systemic injection of the selective μ-opioid receptor antagonist cyprodime (1 mg/kg), demonstrating the involvement of peripheral μ-opioid receptors. Furthermore, the antihyperalgesic effect induced by A-317491, was antagonised by the coadministration of an anti-enkephalin antibody supporting the participation of endogenous enkephalins. Consistent with this result, the antihyperalgesic effect induced by A-317491 was dramatically enhanced by the administration of an enkephalin-degrading inhibitor, Debio 0827, as demonstrated by isobolographic analysis. This synergism opens the theoretical possibility that the combination of both types of drugs could be useful to counteract some nociceptive symptoms derived from tumor development.     

Endocannabinoid-mediated synaptically evoked suppression of GABAergic transmission in the cerebellar cortex

Presynaptic CB₁ cannabinoid receptors are frequently targets of endogenous cannabinoids (endocannabinoids) released from postsynaptic neurons. It is known that the glutamatergic afferent input to a neuron can trigger endocannabinoid production and that the released endocannabinoid can suppress the glutamatergic input. We tested the hypothesis that activation of the glutamatergic input to a neuron leads to an endocannabinoid-mediated suppression of the GABAergic afferent input to the same neuron. Spontaneous postsynaptic currents (sPSCs) were recorded with patch-clamp techniques in Purkinje cells in mouse cerebellar brain slices. Activation of the climbing fiber-mediated glutamatergic input to Purkinje cells led to a suppression of the sPSCs by 34±3%. This suppression was mostly due to suppression of GABAergic spontaneous inhibitory postsynaptic current (sIPSCs), because 93% of the sPSCs recorded in Purkinje cells were GABAergic sIPSCs. Blockade of ionotropic, but not metabotropic glutamate receptors, prevented the suppression. The climbing fiber activation led to an increase in calcium concentration in the Purkinje cells, and this increase was necessary for the suppression of sPSCs, because the suppression did not occur when the calcium increase was prevented by BAPTA. No sPSC suppression was observed in the presence of the CB₁ antagonist rimonabant or the diacylglycerol lipase inhibitor orlistat. In a further series of experiments GABAergic sIPSCs were recorded: these sIPSCs were also suppressed after climbing fiber activation, and the suppression was sensitive to the CB₁ antagonist SLV319. Finally, the GABAergic synaptic transmission between molecular layer interneurons and Purkinje cells was directly studied on simultaneously patch-clamped neuron pairs. Climbing fiber activation led to suppression of the interneuron → Purkinje cell synaptic transmission. The results point to a novel form of endocannabinoid-mediated heterosynaptic plasticity. The endocannabinoid production in a neuron is triggered by its glutamatergic synaptic input and is dependent on an increase in intracellular calcium concentration. The produced endocannabinoid, in turn, suppresses the GABAergic synaptic input to the neuron by activating CB₁ cannabinoid receptors.     

Cardiovascular actions of cannabinoids and their generation during shock

Marijuana is a widely abused recreational drug well known for its psychoactive properties. Cannabinoids, the active ingredients of marijuana, elicit their neurobehavioral effects by interacting with the CB₁ cannabinoid receptor subtype, expressed primarily in the brain but also present in some peripheral tissues. A second receptor subtype, the CB₂ receptor, is expressed on cells of the immune system and is thought to be responsible for the immunosuppressant effects of cannabinoids. Recently, endogenous lipidlike substances have been identified, including arachidonyl ethanolamide (anandamide) and 2-arachidonyl glyceride, that bind to cannabinoid receptors and mimic many of the neurobehavioral effects of plant-derived cannabinoids. Both plant-derived cannabinoids and the endogenous ligands have been shown to elicit hypotension and bradycardia via activation of peripherally located CB₁ receptors. Possible underlying mechanisms include presynaptic CB₁ receptor mediated inhibition of norepinephrine release from peripheral sympathetic nerve terminals, and/or direct vasodilation via activation of vascular cannabinoid receptors. The latter may also be the target of endocannabinoids of vascular endothelial origin. Recent studies indicate that a peripheral endogenous cannabinoid system in circulating macrophages and platelets is activated in hemorrhagic and septic shock and may contribute to the hypotension associated with these conditions via activation of vascular cannabinoid receptors. The potential role of this mechanism in human shock conditions is under investigation. Received: 20 May 1998 / Accepted: 24 August 1998     

CB2 receptor and amyloid pathology in frontal cortex of Alzheimer's disease patients

The cannabinoid system seems to play an important role in various neurodegenerative diseases including Alzheimer's disease (AD). The relationship of cannabinoid receptors (CB₁R and CB₂R) to cognitive function and neuropathological markers in AD remains unclear. In the present study, postmortem cortical brain tissues (Brodmann area 10) from a cohort of neuropathologically confirmed AD patients and age-matched controls were used to measure CB₁R and CB₂R by immunoblotting. Correlational analyses were performed for the neurochemical and cognitive data. CB₁R expression was significantly decreased in AD. Levels of CB₁R correlated with hypophagia, but not with any AD molecular marker or cognitive status (Mini Mental State Examination score). The level of CB₂R was significantly higher (40%) in AD. Increases in the expression of the glial marker glial fibrillar acidic protein were also found. CB₂R expression did not correlate with cognitive status. Interestingly, expression levels of CB₂R correlated with two relevant AD molecular markers, Aβ₄₂ levels and senile plaque score. These results may constitute the basis of CB₂R-based therapies and/or diagnostic approaches.     

Duration-dependent growth of N1m for speech-modulated bone-conducted ultrasound

Cannabinoids classically act via CB₁ and CB₂ receptors to modulate nociception; however, recent findings suggest that some cannabinoids bind to atypical receptors. One such receptor is GPR55 which is activated by the abnormal cannabidiol analogue O-1602. This study investigated whether the synthetic GPR55 agonist O-1602 can alter joint nociception in a rat model of acute joint inflammation. Acute (24 h) inflammatory joint pain was induced in male Wistar rats by intra-articular injection of 2% kaolin and 2% carrageenan. Single unit extracellular recordings were made from arthritic joint afferents in response to mechanical rotation of the knee. Peripheral administration of O-1602 significantly reduced movement-evoked firing of nociceptive C fibres and this effect was blocked by the GPR55 receptor antagonist O-1918. Co-administration of the CB₁ and CB₂ antagonists (AM281 and AM630 respectively) had no effect on O-1602 responses. This study clearly shows that atypical cannabinoid receptors are involved in joint nociception and these novel targets may be advantageous for the treatment of inflammatory pain.     

Inhibition of EphA4 signaling after ischemia-reperfusion reduces apoptosis of CA1 pyramidal neurons

The purinergic receptors P2X₄ and P2X₆ are ion channels activated by ATP. These receptors are present in the gastrointestinal tract, and they are involved in synaptic transmission, taste sensation, and pain, among other functions. In this work, we studied the distribution of P2X₄ and P2X₆ receptors in proximal and distal regions of the gut newborn and adult rats. Using immunohistochemistry, purinergic receptors were found in gut epithelial cells and capillary vessels. In both proximal and distal regions of newborn rats, we observed P2X₄ signal in epithelial cells, whereas P2X₆ was present in capillary vessels in the proximal region and to a lesser extent in the distal region. In both regions of adult gut, we observed P2X₄ and P2X₆ immunostain in the capillary vessels. Semi-quantification indicated a significant difference in the amount of P2X₄ between proximal regions, whereas the P2X₆ content of both newborn regions differed from that in adult proximal gut. We conclude that P2X₄ and P2X₆ purinoreceptors are present in the gut from birth and that they are differentially distributed among regions.     

Development of P2X receptor clusters on smooth muscle cells in relation to nerve varicosities in the rat urinary bladder

Postnatal development of the distribution of different isoforms of purinergic (P2X) receptors on smooth muscle cells in relation to the development of the innervation of the cells by nerve varicosities in the rat urinary bladder has been determined with immunofluorescence and confocal microscopy. Antibodies against the extracellular domains of the P2X₁ to P2X₆ receptors were used to detect the receptors in the bladder. Several other antibodies were used to identify sympathetic varicosities and Schwann cells. At one day postnatal (D1) there were few strings of varicosities denoting isolated axons, with most axons confined to large nerve trunks. Small size clusters of P2X₁ to P2X₆ receptor subtypes (about 0.4 µm diameter) were observed in the muscle which were independent of each other, and sometimes juxtaposed to the rare isolated varicosity strings. At D4 large numbers of strings of varicosities could be discerned throughout the detrusor. Most of these clouds of small P2X₁ to P2X₆ receptor clusters in their immediate vicinity. Some of these were colocalised with the varicosities, which were of parasympathetic origin as they failed to counter-stain with antibodies to tyrosine hydroxylase. Up to D14 there was a gradual coalescence of many of the isolated P2X_1–6 small receptor clusters so that they became colocalised, often at varicosities. Most of the varicosities in isolated strings possessed receptor clusters at this time. By D21 it was rare to find varicosity strings in the detrusor that were not either in close juxtaposition with P2X small receptor clusters or possessing such clusters in colocalisation. However, large numbers of small P2X receptor clusters, many of which consisted of a mixture of isoforms, could be found spatially unrelated to nerve varicosities throughout the detrusor muscle. In the adult, single axons were either coextensive with one or more isoforms of P2X receptor clusters or these were immediately juxtaposed to the axons so that is was rare to find a varicosity that did not possess a receptor cluster. However, different combinations of colocalised P2X receptor isoforms could still be discerned in small clusters unrelated to varicosities. These observations are discussed in relation to the mechanism of formation of the receptor clusters and their migration beneath parasympathetic varicosities during development.     

Facilitation of Ih channels by P2Y1 receptors activation in Mesencephalic trigeminal neurons

P2Y₁ receptors, a subset of G-protein coupled receptors, have been shown to participate in sensory transduction in the periphery nervous system. However, little is known about their sensory function in the central nervous system. Here, by using immunohistochemistry, we showed that P2Y₁ receptors are predominantly localized in the somata of Mesencephalic trigeminal neurons (Mes V neurons), the primary sensory neurons in brainstem. Whole-cell voltage-clamp recording revealed that ADP-β-S, a P2Y receptor agonist, enhanced the activity of hyperpolarization-activated cation channels (Ih channels) in Mes V neurons and that the activity-enhancing effect of ADP-β-S could be blocked by a specific P2Y₁ receptor antagonist, MRS 2179. Taken together, these results suggested a possible role of P2Y₁ receptors in the information transduction of central sensory neurons through regulating Ih channel activities.     

In vivo motor effects of loperamide on the rat urinary bladder

Bladder motility recordings were performed in anaesthetized rats and the effect of the peripherally active opiate agonist loperamide on urinary bladder function was studied. Regional intra-arterial administration of loperamide (0.01–2 mg kg^-1) induced weak bladder contraction per se. Loperamide caused an effective dose-dependent inhibition of bladder motility induced by regional injection of the receptor agonists acetylcholine (ACh) and substance P (SP), as well as by peripheral motor nerve stimulation (PNS). Pretreatment with naloxone (0.5 mg kg^-1) partially antagonized the inhibitory action of loperamide on the nerve-mediated detrusor contraction. However, the depression of the motor responses induced by the receptor agonists ACh and SP was not influenced. It is suggested that the demonstrated inhibitory effect of loperamide on bladder motility is partially mediated by peripheral opioid receptors. The main non-opioid part of the inhibition might be a direct smooth muscle action.     

Cyclooxygenase inhibitors suppress the expression of P2X3 receptors in the DRG and attenuate hyperalgesia following chronic constriction injury in rats

Recent evidence suggests that P2X₃ receptors express abundantly in nociceptive sensory neurons and play an important role in neuropathic pain. Upregulation of prostaglandin E2 (PGE2) after nerve injure is involved in the pathogenesis of neuropathic pain. An increase of P2X₃ receptors after chronic constriction injury (CCI) to the sciatic nerve has also been reported, the mechanisms are not known clearly. In this study, we examined the effects of systemic administration of cyclooxygenase (COX) inhibitors on analgesia and the expression of P2X₃ receptors in the dorsal root ganglia (DRG) in CCI rats. Rats received 0.9% saline, the nonselective COX inhibitor ibuprofen (40 mg kg⁻¹ day⁻¹) or the selective COX-2 inhibitor celecoxib (30 mg kg⁻¹ day⁻¹) by gavage twice daily from 3 to 14 days after surgery. Mechanical allodynia and thermal hyperalgesia induced by CCI were markedly attenuated by celecoxib from 5 to 14 days after surgery, and relieved by ibuprofen treatment from 7 to 10 days after surgery. The increase of P2X₃ receptors in the DRG in CCI rats on day 14 after surgery was also significantly inhibited; the effect of ibuprofen was stronger than that of celecoxib. These results demonstrate that up-regulated COX/PGE2 after nerve damage may play an important role in neuropathic pain. They are highly involved in the expression of P2X₃ receptors in the DRG in CCI rats.     

Morphological and functional changes of free sensory receptors of the frog urinary bladder during regeneration

Dynamics of morphological and functional changes of bush-like sensory receptors including free visceroreceptors of the frog urinary bladder were investigated. For this purpose surgical operation was performed to intersect the ischiococcygeal plexus. It was demonstrated that 1) receptors can generate spontaneous impulse activity up to 18th postoperative day. In this stage one part of afferent fibres was left undamaged, although the others demonstrated the Wallerian degeneration features; 2) regeneration of fibres began after a postoperative month 3) first remyelinated fibres were registered in nerve bundles following 2-3 months; at the same time non myelinated distal regions left bundles and form non myelinated arbors in the surrounding tissues. The receptor impulse activity was registered simultaneously; 4) morphological features of growing bush-like receptors at light optic level differed from those in native state; 5) maturation of regenerating receptors was finished a year later.     

Effect of chronic activation of 5-HT3 receptors on 5-HT3, 5-HT1A and 5-HT2A receptors functional activity and expression of key genes of the brain serotonin system

Among serotonin (5-HT) receptors, the 5-HT₃ receptor is the only ligand-gated ion-channel. Little is known about the interaction between the 5-HT₃ receptor and other 5-HT receptors and influence of 5-HT₃ chronic activation on other 5-HT receptors and the expression of key genes of 5-HT system. Chronic activation of 5-HT₃ receptor with intracerebroventricularly administrated selective agonist 1-(3-chlorophenyl)biguanide hydrochloride (m-CPBG) (14 days, 40 nmol, i.c.v.) produced significant desensitization of 5-HT₃ and 5-HT_1A receptors. The hypothermic responses produced by acute administration of selective agonist of 5-HT₃ receptor (m-CPBG, 40 nmol, i.c.v.) or selective agonist of 5-HT_1A receptor (8-hydroxy-2-(di-n-propylamino)tetralin) (8-OH-DPAT, 1 mg/kg, i.p.) was significantly lower in m-CPBG treated mice compared with the mice of control groups. Chronic m-CPBG administration failed to induce any significant change in the 5-HT_2A receptor functional activity and in the expression of the gene encoding 5-HT_2A receptor. Chronic activation of 5-HT₃ receptor produced no considerable effect on the expression on 5-HT₃, 5-HT_1A, and 5-HT transporter (5-HTT) and tryptophan hydroxylase-2 (TPH-2) genes – the key genes of brain 5-HT system, in the midbrain, frontal cortex and hippocampus. In conclusion, chronic activation of ionotropic 5-HT₃ receptor produced significant desensitization of 5-HT₃ and postsynaptic 5-HT_1A receptors but caused no considerable changes in the expression of key genes of the brain 5-HT system.     

Beneficial effects of cannabinoids (CB) in a murine model of allergen-induced airway inflammation: role of CB1/CB2 receptors

The endocannabinoid system (ECS) consists of two cannabinoid (CB) receptors, namely CB₁ and CB₂ receptor, and their endogenous (endocannabinoids) and exogenous (cannabinoids, e.g. delta-9-tetrahydrocannabinol (THC)) ligands which bind to these receptors. Based on studies suggesting a role of THC and the ECS in inflammation, the objective of this study was to examine their involvement in type I hypersensitivity using a murine model of allergic airway inflammation. THC treatment of C57BL/6 wildtype mice dramatically reduced airway inflammation as determined by significantly reduced total cell counts in bronchoalveolar lavage (BAL). These effects were greatest when mice were treated during both, the sensitization and the challenge phase. Furthermore, systemic immune responses were significantly suppressed in mice which received THC during sensitization phase. To investigate a role of CB_1/2 receptors in this setting, we used pharmacological blockade of CB₁ and/or CB₂ receptors by the selective antagonists and moreover CB₁/CB₂ receptor double-knockout mice (CB₁^−/−/CB₂^−/−) and found neither significant changes in the cell patterns in BAL nor in immunoglobulin levels as compared to wildtype mice. Our results indicate that the activation of the ECS by applying the agonist THC is involved in the development of type I allergies. However, CB₁/CB₂ receptor-independent signalling seems likely in the observed results.