An analgesia circuit activated by cannabinoids

Although many anecdotal reports indicate that marijuana and its active constituent, delta-9-tetrahydrocannabinol (delta-9-THC), may reduce pain sensation, studies of humans have produced inconsistent results. In animal studies, the apparent pain-suppressing effects of delta-9-THC and other cannabinoid drugs are confounded by motor deficits. Here we show that a brainstem circuit that contributes to the pain-suppressing effects of morphine is also required for the analgesic effects of cannabinoids. Inactivation of the rostral ventromedial medulla (RVM) prevents the analgesia but not the motor deficits produced by systemically administered cannabinoids. Furthermore, cannabinoids produce analgesia by modulating RVM neuronal activity in a manner similar to, but pharmacologically dissociable from, that of morphine. We also show that endogenous cannabinoids tonically regulate pain thresholds in part through the modulation of RVM neuronal activity. These results show that analgesia produced by cannabinoids and opioids involves similar brainstem circuitry and that cannabinoids are indeed centrally acting analgesics with a new mechanism of action.

Pain: nocistatin spells relief

Tissue or nerve injury can dramatically alter the transmission of sensory stimuli by spinal cord neurons, so that a light touch produces pain. The discovery that peptide products of prepronociceptin processing either facilitate or inhibit these mechanisms suggests novel approaches to treating these conditions.

Cannabinoid receptor-mediated inhibition of the rat tail-flick reflex after microinjection into the rostral ventromedial medulla

Systemic administration of cannabinoids produce profound antinociception in rodents. The purpose of this study was to examine the contribution of the rostral ventromedial medulla (RVM) to cannabinoid-mediated inhibition of the tail-flick reflex. Rats received direct injections of two selective cannabinoid agonists, WIN55,212-2 and HU210, into the RVM. Both compounds significantly elevated tail-flick latencies by over 50%. WIN55,212-3, the inactive enantiomer, was without effect. Furthermore, co-administration of the selective cannabinoid receptor antagonist, SR141716A greatly attenuated the antinociception produced by HU210. Finally, injections of WIN55,212-2 outside the region of the RVM did not affect tail-flick latencies. These results demonstrate that the cannabinoid receptor system participates in the descending control of nociception and raise the possibility that actions of endogenous cannabinoids in the RVM may modulate nociceptive responsiveness.

Nonimmune phagocytosis of liposomes by rat alveolar macrophages is enhanced by vitronectin and is vitronectin-receptor mediated

Pulmonary alveolar macrophages (AMs) engulf diverse materials. The mechanisms allowing AMs to recognize, bind, and phagocytose these materials are poorly understood. To test the hypothesis that the adhesive glycoprotein vitronectin (Vn) acts as a nonimmune opsonin, we studied AM-Vn binding and AM phagocytosis of fluorescent liposomes under the following conditions: (1) pretreatment of AMs with Vn, followed by incubation of AMs with liposomes containing increased amounts of Vn; (2) inhibition of phagocytosis by gly-arg-gly-asp-ser (RGD) and gly-pen-gly-arg-gly-asp-ser-pro-cys-ala (GPen); and (3) antibody blockade of the alpha(v)beta3 vitronectin receptor (VnR). Pretreatment of AMs with 0.1, 1, and 2 microM Vn progressively enhanced AM-Vn binding from 23,622 +/- 3,328 cpm to 40,847 +/- 6,530 cpm, 57,149 +/- 2,789 cpm, and 124,852 +/- 42,930 cpm, respectively (P < 0.05). AM pretreatment also increased phagocytosis of Vn-enriched liposomes, but not empty liposomes (20.7 +/- 0.4 liposomes/cell versus 11.5 +/- 0.5 liposomes/cell, P < 0.05). Moreover, increased concentrations of Vn in liposomes progressively increased phagocytic activity (3.7 +/- 0.3, 6.5 +/- 0.2, 11.5 +/- 0.5, and 16.5 +/- 0.6 liposomes/cell with 0.01, 0.1, and 1 microM Vn, respectively, P < 0.05). RGD inhibited Vn-enhanced phagocytosis (8.1 +/- 0.4 liposomes/cell to 3.4 +/- 0.2, 2.4 +/- 0.4, and 2.2 +/- 0.2 liposomes/cell with 0.02, 0.2, and 2 mM RGD, respectively, P < 0.05), as did GPen (4.7 +/- 0.8 liposomes/cell versus control = 10.9 +/- 1.5 liposomes/cell, P < 0.05) and anti-VnR antibody (3.3 +/- 0.4 liposomes/cell versus control = 8.9 +/- 1.7 liposomes/cell, P < 0.05). We conclude that AMs employ Vn as a nonimmune opsonin to enhance the efficiency of phagocytosis.

Surfactant protein A (SP-A) mediates attachment of Mycobacterium tuberculosis to murine alveolar macrophages

Attachment of Mycobacterium tuberculosis organisms to alveolar macrophages (AMs) is an essential early event in primary pulmonary tuberculosis. Surfactant protein A (SP-A) is a nonimmune opsonin present in the alveolar spaces that binds carbohydrate residues such as mannose. It was hypothesized that SP-A attaches to M. tuberculosis and serves as a ligand between M. tuberculosis and AMs. [125I]SP-A was found to bind to M. tuberculosis in a time- and [Ca2+]-dependent manner with a Kd of 1.9 x 10(-9) M and an apparent number of 6.3 x 10(2) SP-A binding sites/organism. Further, deglycosylated SP-A had minimal binding to M. tuberculosis, indicating that sugar moieties are important in this interaction. SP-A specifically binds to a 60-kD cell-wall protein from M. tuberculosis. SP-A-mediated attachment of 51Cr-labeled M. tuberculosis organisms to AMs is dependent on time, SP-A concentration, and Ca2+. M. tuberculosis attachment to murine AMs in the absence of SP-A was 12.8 +/- 0.9%; however, in the presence of 5 microg/ml SP-A the attachment increased to 38.6 +/- 2.9% (P < 0.001). SP-A-mediated attachment was significantly decreased from 38.6 +/- 2.9% to 18.7 +/- 3.3% (P < 0.05) in the presence of antihuman SP-A antibodies. When the attachment assay was repeated in the presence of alpha-methylene-D-mannosepyranosidase (mannosyl-BSA) and type V collagen, SP-A-mediated attachment decreased from 38.6 +/- 2.9% to 16.6 +/- 1.5% (P < 0.001) and 19.1 +/- 1.4% (P < 0.05), respectively. Further, deglycosylated SP-A had only a minimal effect on M. tuberculosis attachment to AMs. These data indicate that SP-A can mediate M. tuberculosis attachment to AMs, and suggest possible underlying mechanisms for this.

Stealth virus epidemic in the Mohave Valley. I. Initial report of virus isolation

Increasing numbers of patients within the Mohave Valley region of the United States are reporting symptoms attributable to atypical neurological illness. Many of these patients have experienced an acute-onset gastrointestinal illness during the spring and summer of 1996. Stealth viral cultures performed on the blood of 40 of these patients have been uniformly positive, yielding unequivocal transmissible cytopathic effect (CPE) in both human- and monkey-derived cell lines. One patient has died from a stealth-CPE-positive glioblastoma, while another patient has developed a plemorphic adenoma of the parotid. Viral cultures and epidemiological data support human-to-human, and probable human-to-dog, transmission of the Mohave stealth virus infection.

Detection of RNA sequences in cultures of a stealth virus isolated from the cerebrospinal fluid of a health care worker with chronic fatigue syndrome. Case report

A cytopathic stealth virus was cultured from the cerebrospinal fluid of a nurse with chronic fatigue syndrome. Reverse transcriptase-polymerase chain reaction (RT-PCR) performed on the patient's culture yielded positive results with primer sets based on sequences of a previously isolated African green monkey simian-cytomegalovirus-derived stealth virus. The same primer sets did not yield PCR products when tested directly on DNA extracted from the cultures. The findings lend support to the possibility of replicative RNA forms of certain stealth viruses and have important implications concerning the choice of therapy in this type of patient.

Suppression of noxious stimulus-evoked activity in the ventral posterolateral nucleus of the thalamus by a cannabinoid agonist: correlation between electrophysiological and antinociceptive effects

The CNS contains a putative cannabinergic neurotransmitter and an abundance of G-protein-coupled cannabinoid receptors. However, little is known about the function of this novel neurochemical system. Cannabinold agonists produce antinociception in behavioral tests, suggesting the possibility that this system serves in part to modulate pain sensitivity. To explore this possibility, the effects of the cannabinoid agonist WIN 55,212-2 on nociceptive neurons in the ventroposterolateral (VPL) nucleus of the thalamus were examined in urethane-anesthetized rats. After identification of a nociresponsive neuron, a computer-controlled device delivered graded pressure stimuli to the contralateral hindpaw. WIN 55,212-2 (0.0625, 0.125, and 0.25 mg/kg, i.v.) suppressed noxious stimulus-evoked activity of VPL neurons in a dose-dependent and reversible manner. Noxious stimulus-evoked firing was affected more than spontaneous firing. These effects were apparently mediated by cannabinoid receptors, because the cannabinoid receptor-inactive enantiomer of the drug (WIN 55,212-3, 0.25 mg/kg) failed to alter the activity of this population of cells. Administration of morphine (0.5 mg/kg, i.v.) produced effects that were very similar to those produced by the cannabinoid. WIN 55,212-2 (0.25 mg/kg, i.v.) failed to alter the responses of non-nociceptive low-threshold mechanosensitive neurons in the VPL WIN 55,212-2 produced antinociceptive effects with a potency and time course similar to that observed in the electrophysiological experiments, despite the differences in the anesthetic states of the animals used in these experiments. The antinociceptive and electrophysiological effects on VPL neurons outlasted the motor effects of the drug. Furthermore, the changes in nociceptive responding could not be attributed to changes in skin temperature. Taken together, these findings suggest that cannabinoids decrease nociceptive neurotransmission at the level of the thalamus and that one function of endogenous cannabinoids may be to modulate pain sensitivity.

Assessment of in vivo attachment/phagocytosis by alveolar macrophages

Alveolar macrophages (AMs) are recognized as an important first line of cellular host defense within the lung. Although mechanisms underlying AM response to microorganisms or particulates are well characterized in vitro, experimental approaches to the study of AMs in vivo are limited. To circumvent these limitations, a new assay was developed using fluorescently labelled liposomes or Pneumocystis carinii (PC) organisms which were administered intratracheally into mechanically ventilated rats. After 30 min, the lungs were lavaged and the percentage of administered liposomes or PC bound to AMs was determined by quantifying fluorescence. Factors known to enhance attachment/phagocytosis by AMs in vitro were assayed to determine their effect in vivo. For example, vitronectin (VN)-coated liposomes increased attachment from 25.2 +/- 2.4% to 47.2 +/- 3.0% (p < 0.001), while addition of VN increased the binding of PC to AMs from 16.5 +/- 1.7% to 24.5 +/- 2.2% (p < 0.05). Confocal laser microscopy of cells obtained by lavage provided morphologic evidence of attachment/phagocytosis by AMs. This model will permit the quantitative assessment of the interaction of fluorescently labelled liposomes or microorganisms with AMs in the lower respiratory tract of living animals.

Human surfactant protein A enhances attachment of Pneumocystis carinii to rat alveolar macrophages

Pneumocystis carinii (PC) pneumonia remains one of the most important opportunistic pulmonary infections. The alveolar macrophage (AM) is likely the primary cell for recognition and removal of PC. The histopathology of PC pneumonia is characterized by a surfactant-like alveolar exudate. We hypothesize that surfactant protein A(SP-A), the major apoprotein of surfactant, mediates attachment of PC to rat AMs by acting as a ligand between the organism and the AM. In this study, attachment of PC was determined using (51)Cr-labeled PC incubated at 4 degrees C with normal rat AM monolayers in the presence or absence of human SP-A. SP-A significantly enhanced attachment of PC from 14.2 +/- 1.2% to 42.0 +/- 3.8% (P<0.05). This enhanced attachment was visualized and quantified morphologically with confocal microscopy. PC attachment by SP-A was calcium- and mannose-dependent as SP-A-mediated attachment was significantly reduced in the presence of EGTA and mannose to 13.1 +/- 1.6% and 19.3 +/- 2.6%, respectively (P<0.05). Addition of type V collagen and antibodies to SP-A also significantly reduced SP-A-mediated attachment to 4.9 +/- 1.2% and 10.1 +/- 1.2%, respectively (P<0.05). We conclude that SP-A can function as a ligand between PC and the AM and may represent an important detection and clearance mechanism of PC from the alveolar spaces.

Functional impairment of bronchoalveolar lavage phospholipids in early Pneumocystis carinii pneumonia in rats

Surfactant abnormalities may contribute to the impairment of gas exchange observed in Pneumocystis carinii pneumonia. Analysis of rat bronchoalveolar lavage (BAL) lipid extracts from normal controls, steroid controls, trimethaprim-sulfamethoxazole (TMP-SMX) controls, TMP-SMX/P. carinii pneumonia controls, and P. carinii pneumonia animals reveal similar total phospholipid and total protein levels. However, there was a marked reduction in phosphatidylglycerol (PG) from the BAL of P. carinii pneumonia rats as compared with control animals, with a decrease from 4.91 +/- 1.29 nmol/mg protein to 0.46 +/- 0.57 nmol/mg protein (p<0.05) and a decrease, as a percent of total phospholipids, from 7.7% +/- 0.88% to 0.91% +/- 0.59% (p<0.001). Furthermore, in vitro surface activities of BAL lipid extracts from control and P. carinii pneumonia rats revealed minimum surface tension increases from 9.38 +/- 1.71 mN/m in controls to 16.36 +/- 0.83 mN/m in P. carinii pneumonia rats (p<0.05) and likewise maximum surface tension increases from 22.14 +/- 4.34 mN/m to 38.57 +/- 2.07 mN/m (p<0.01). Of interest, the surface activity of PG-deficient P. carinii pneumonia BAL lipid extracts is completely restored to that of normal controls by the addition of exogenous PG. These findings suggest that a functionally abnormal surfactant occurs in P. carinii pneumonia and that this may account, in part, for the impairment of gas exchange observed in this disorder.

Suppression of noxious stimulus-evoked expression of Fos protein-like immunoreactivity in rat spinal cord by a selective cannabinoid agonist

In rats, cannabinoids inhibit behavioral responses to noxious stimulation with a potency and efficacy similar to that of morphine. However, because cannabinoids depress motor function, it has not been possible to state beyond any doubt that these effects were related to a dampening of noxious sensory input. Therefore, c-fos immunocytochemistry was used to explore the possibility that cannabinoids reduce behavioral responses to noxious stimuli by decreasing spinal processing of nociceptive inputs. Rats received systemic injections of the potent and selective cannabinoid agonist WIN 55,212-2, the receptor-inactive enantiomer WIN 55,212-3 or vehicle prior to observations in a model of tonic pain, the formalin test. As demonstrated previously, plantar injections of formalin led to lifting and licking of the injected paw, with two peaks of activity occurring at 5 and 30 min after injection. The cannabinoid agonist suppressed these pain responses and produced a reduction in mobility. Immunocytochemical processing of sections with an antibody to the Fos protein revealed that the cannabinoid markedly suppressed pain-evoked c-fos expression in the superficial and neck regions of the spinal dorsal horn, but not in the nucleus proprius. Decreased expression of c-fos also occurred in the ventral horn. The specificity of this effect and its probable mediation by cannabinoid receptors are suggested by three findings: (i) the suppression by the drug of both behavioral and immunocytochemical responses to pain was dose-dependent; (ii) neither the behavioral nor the immunocytochemical response to the noxious stimulus was significantly affected by the receptor-inactive enantiomer of the agonist; (iii) animals rendered tolerant to cannabinoids by repeated injections of the agonist showed reduced responses to the drug. These findings suggest that cannabinoids inhibit the spinal processing of nociceptive stimuli and support the notion that endogenous cannabinoids may act naturally to modify pain trnasmission within the central nervous system.

Simian cytomegalovirus-related stealth virus isolated from the cerebrospinal fluid of a patient with bipolar psychosis and acute encephalopathy

A cytopathic 'stealth' virus was cultured from the cerebrospinal fluid of a patient with a bipolar psychotic disorder who developed a severe encephalopathy leading to a vegetative state. DNA sequencing of a polymerase chain reaction-amplified product from infected cultures has identified the virus as an African green monkey simian cytomegalovirus (SCMV)-related stealth virus. The virus is similar to the SCMV-related stealth virus isolated from a patient with chronic fatigue syndrome. The findings support the concepts that stealth viruses can account for a spectrum of dysfunctional brain diseases and that some of these viruses may have arisen from live polio viral vaccines.

Severe stealth virus encephalopathy following chronic-fatigue-syndrome-like illness: clinical and histopathological features

The clinical histories and brain biopsy findings of 3 patients with severe stealth virus encephalopathy are reviewed. The patients initially developed symptoms consistent with a chronic fatigue syndrome. One patient has remained in a vegetative state for several years, while the other 2 patients have shown significant, although incomplete, recovery. Histological and electron-microscopic studies revealed vacuolated cells with distorted nuclei and various cytoplasmic inclusions suggestive of incomplete viral expression. There was no significant inflammatory response. Viral cultures provided further evidence of stealth viral infections occurring in these patients.

Stealth viral encephalopathy: report of a fatal case complicated by cerebral vasculitis

A patient presenting with a severe subacute encephalopathy was shown to be infected with a stealth virus. Although the patient partially recovered, he remained lethargic with cognitive impairment and worsening headaches. Ten months after the onset of his illness, his clinical condition further deteriorated with seizures, coma and death. A brain biopsy revealed vacuolated degenerate neural cells consistent with a stealth viral encephalopathy. Focal perivascular lymphocytic inflammation was present within the leptomeninges and to a lesser extent within the parenchyma of the brain. Vasculitis may occasionally contribute to the complex symptomatology of stealth viral encephalopathy.

Genetic instability and fragmentation of a stealth viral genome

Partial sequencing was performed on cloned DNA obtained from cultures of a stealth virus isolated from a patient with the chronic fatigue syndrome. The results extend earlier findings showing regions of homology to cytomegalovirus (CMV). Although the virus is much more closely related to simian CMV than to human CMV, many of the cloned viral segments could be aligned with the human CMV genome. The aggregate size of the aligned segments exceeds 100 kilobase pairs (kbp). Undigested viral DNA has a mobility in agarose gel electrophoresis corresponding to approximately 20 kbp. The virus, therefore, apparently exists in multiple fragments. Considerable sequence variation exists between individual clones which overlap to similar regions of the human CMV genome. The fragmented genome and sequence microheterogeneity suggest that both the processivity and the fidelity of replication of the viral genome are defective. An unstable viral genome may provide a potential mechanism of recovery from stealth viral illness.

Role of surfactant protein A in the pathogenesis of tuberculosis in subjects with human immunodeficiency virus infection

Human immunodeficiency virus (HIV)-infected subjects are at increased risk for tuberculosis even before there is a significant loss of CD4 lymphocytes. A factor was found to be present in the bronchoalveolar lavage (BAL) of HIV-infected subjects that promoted the attachment of M. tuberculosis (MTB) organisms to alveolar macrophages (AMs). Using 51Cr-labeled MTB organisms, BAL from control subjects resulted in MTB attachment to AMs at 11.6% +/- 1.0%; in contrast, BAL from HIV-infected subjects increased attachment to 33.1% +/- 3.8% (P < 0.001). Surfactant protein A (SP-A) levels in BAL of normal controls was 1.9 +/- 0.3 micrograms/ml and was 5.5 +/- 0.4 micrograms/ml in the BAL of HIV-infected subjects (P < 0.01). When SP-A was removed by immunoprecipitation from the BAL of HIV-infected subjects, MTB attachment decreased from 33.1% +/- 3.8% to 11.3% +/- 0.4% (P < 0.001), a value identical to control levels. Exogenous human SP-A (5 micrograms/ml) was added back to the immunoprecipitated BAL and the enhanced attachment of MTB was restored. These data suggest that BAL from HIV-infected subjects contain a factor that facilitates MTB attachment to AMs, the first critical step in the establishment of infection. This factor appears to be SP-A.

Murine laminin binds to Histoplasma capsulatum. A possible mechanism of dissemination

Histoplasmosis, an increasingly important opportunistic infection in immunosuppressed subjects, is characterized by hematogenous dissemination of the yeast from the lung. The mechanism of this dissemination is not fully understood. Laminin, the major glycoprotein of the extracellular matrix, is known to mediate the attachment of various invasive pathogens to host tissues. In the current study, laminin is demonstrated to bind to Histoplasma capsulatum in a rapid, specific, and saturable manner. Scatchard analysis with 125I-labeled laminin revealed an estimated 3.0 x 10(4) binding sites per yeast with an apparent Kd for laminin binding of 1.6 x 10(-9) M. Laminin binding to H. capsulatum was decreased from 62 +/- 1 to 17 +/- 1 ng (P < 0.001) in the presence of 3,000 nM of Ile-Lys-Val-Ala-Val, a pentapeptide within one major cell attachment site of laminin. A 50-kD H. capsulatum laminin-binding protein was demonstrated using an 125I-Ln blot of H. capsulatum cell wall proteins. The 50-kD protein is also recognized by antibodies directed at the 67-kD laminin receptor, suggesting they are related. This study proposes a possible mechanism for H. capsulatum attachment to laminin, an important first step required for the yeast to recognize and traverse the basement membrane.

Cesarean section in a pregnant patient with an anterior mediastinal mass and failed supradiaphragmatic irradiation

Nodular sclerosing Hodgkin's disease stages IA and IIA are the most common presentation of this disease during pregnancy. Patients presenting with late Hodgkin's disease with failed irradiation for cesarean section present a unique challenge. When this presentation occurs, a voluntary interruption of pregnancy is recommended. Upper body irradiation during the second trimester of pregnancy is recommended as well. We report a case involving a pregnant patient at 34 weeks' gestation presenting for cesarean section with a symptomatic anterior mediastinal mass occupying over 50% of the thoracic diameter. The anesthetic management was performed using continuous spinal.

Surfactant protein a promotes attachment of Mycobacterium tuberculosis to alveolar macrophages during infection with human immunodeficiency virus

The incidence of tuberculosis is increasing on a global scale, in part due to its strong association with human immunodeficiency virus (HIV) infection. Attachment of Mycobacterium tuberculosis to its host cell, the alveolar macrophage (AM), is an important early step in the pathogenesis of infection. Bronchoalveolar lavage of HIV-infected individuals demonstrated the presence of a factor which significantly enhances the attachment of tubercle bacilli to AMs 3-fold relative to a normal control population. This factor is surfactant protein A (SP-A). SP-A levels are increased in the lungs of HIV-infected individuals. SP-A levels and attachment of M. tuberculosis to AMs inversely correlate with peripheral blood CD4 lymphocyte counts. Elevated concentrations of SP-A during the progression of HIV infection may represent an important nonimmune risk factor for acquiring tuberculosis, even before significant depletion of CD4 lymphocytes in the peripheral blood occurs.

An examination of the central sites of action of cannabinoid-induced antinociception in the rat

Microinjections of low doses of the potent and selective cannabinoids WIN 55,212-2 and CP 55,940 into the lateral ventricle produce long-lasting reduction in sensitivity to noxious thermal stimuli (1). To determine the central distribution of ventricularly administered WIN 55,212-2, we microinjected an analgesic dose of the drug with [3H]WIN 55,212-2. At the peak time of antinociception, the radiolabeled drug was confined to periventricular sites throughout the brain. The contribution of particular periventricular structures to the antinociceptive effect was evaluated using intracerebral microinjection techniques and the tail-flick test. Guide cannulae were implanted above the following periventricular structures: the medial septal area, lateral habenlua, perihypothalamic area, arcuate nucleus of the hypothalamus, dorsal raphe nucleus and the dorsolateral and ventrolateral aspects of the periaqueductal gray. Microinjections of WIN 55,212-2 (5 micrograms/0.5 microliter) into the medial septal area, lateral habenula, perihypothalamic area, arcuate nucleus, and ventrolateral periaqueductal gray did not significantly affect tail-flick latencies. By contrast, microinjections of WIN 55,212-2 into the dorsolateral periaqueductal gray and the dorsal raphe significantly elevated tail-flick latencies. The results of this study indicate that at least two periventricular structures within the brain are involved in cannabinoid antinociception.

Inhibition of noxious stimulus-evoked activity of spinal cord dorsal horn neurons by the cannabinoid WIN 55,212-2

The effects of a potent synthetic cannabinoid WIN 55,212-2 on nociceptive responses of wide dynamic range (WDR) neurons in the lumbar spinal cord were investigated in anesthetized rats. WDR neurons were identified by their responses to innocuous brushing and to a range of pressure stimuli from innocuous to noxious. Noxious pressure was applied to regions of the ipsilateral hind paw corresponding to the receptive field of the neuron. WIN 55,212-2 (125 micrograms/kg and 250 micrograms/kg, i.v.) produced a profound inhibition of firing evoked by the noxious pressure stimulus. By contrast, the cannabinoid did not alter the evoked activity of non-nociceptive neurons in response to non-noxious levels of stimulation. Treatment with either vehicle or the inactive enantiomer WIN 55,212-3 (250 micrograms/kg) failed to alter noxious stimulus-evoked activity of WDR neurons. These data provide direct evidence for cannabinoid-mediated inhibition of pain neurotransmission in the spinal dorsal horn. The site of action for these effects remains to be determined.

Fluorescent liposomes as quantitative markers of phagocytosis by alveolar macrophages

A new phagocytic assay based on liposome ingestion by alveolar macrophages (AMs) is described. Fluorescent microspheres were encapsulated in liposomes, which allowed rapid enumeration by fluorometry. Liposomes made in the presence of vitronectin had the protein exposed on their outer surfaces, as determined by immunolabelling. Liposomes and rat AMs were incubated under conditions favorable for phagocytosis. Observation by light and electron microscopy showed AMs engulfing liposomes, with gradual transfer of fluorescent label from liposome to cell interior. This transfer was due to bona fide phagocytosis, as evidenced by (1) fluorescence of liposome-encapsulated dihydrofluorescein (DHF)-zymosan exclusively within AMs and (2) triggering of the respiratory burst by zymosan-associated liposomes only under conditions that allowed phagocytosis. Phagocytic activity was expressed as liposomes/cell, the average number of liposomes phagocytosed per macrophage. We used this technique to follow phagocytosis over time and to measure the effects of lipopolysaccharide (LPS) and vitronectin on AM phagocytosis.