Optogenetic silencing of a corticotropin-releasing factor pathway from the central amygdala to the bed nucleus of the stria terminalis disrupts sustained fear.

The lateral central nucleus of the amygdala (CeAL) and the dorsolateral bed nucleus of the stria terminalis (BNSTDL) coordinate the expression of shorter- and longer-lasting fears, respectively. Less is known about how these structures communicate with each other during fear acquisition. One pathway, from the CeAL to the BNSTDL, is thought to communicate via corticotropin-releasing factor (CRF), but studies have yet to examine its function in fear learning and memory. Thus, we developed an adeno-associated viral-based strategy to selectively target CRF neurons with the optogenetic silencer archaerhodopsin tp009 (CRF-ArchT) to examine the role of CeAL CRF neurons and projections to the BNSTDL during the acquisition of contextual fear. Expression of our CRF-ArchT vector injected into the amygdala was restricted to CeAL CRF neurons. Furthermore, CRF axonal projections from the CeAL clustered around BNSTDL CRF cells. Optogenetic silencing of CeAL CRF neurons during contextual fear acquisition disrupted retention test freezing 24 h later, but only at later time points (>6 min) during testing. Silencing CeAL CRF projections in the BNSTDL during contextual fear acquisition produced a similar effect. Baseline contextual freezing, the rate of fear acquisition, freezing in an alternate context after conditioning and responsivity to foot shock were unaffected by optogenetic silencing. Our results highlight how CeAL CRF neurons and projections to the BNSTDL consolidate longer-lasting components of a fear memory. Our findings have implications for understanding how discrete amygdalar CRF pathways modulate longer-lasting fear in anxiety- and trauma-related disorders.

Effects of recording media composition on the responses of Nafion-coated carbon fiber microelectrodes measured using high-speed chronoamperometry.

The present study concerns methodological issues of electrochemical recordings using Nafion-coated 30 microm diameter single carbon fiber microelectrodes for high-speed chronoamperometric measurements of biogenic amines. First, the single carbon fiber microelectrodes were coated with Nafion and dried at 85 vs. 200 degrees C and their recording properties were determined. Second, the effects of shifts in solution pH, ionic strength, changes in recording solution levels of Ca(2+) or Mg(2+) and temperature on the recording characteristics and sensitivity of Nafion-coated high temperature dried (200 degrees C) single carbon fiber microelectrodes for measures of dopamine were studied. These studies showed that the high temperature drying of the Nafion produced a microelectrode with better recording properties: higher selectivity for cations versus anions, increased differences between the reduction and oxidation current ratios for the identification of dopamine versus serotonin, and more rapid response times. In addition, these studies demonstrated that the chronoamperometric recordings were insensitive to small changes in pH and divalent cations such as Ca(2+) or Mg(2+). However, increases in ionic strength decreased the sensitivity of the microelectrodes, while increases in temperature produced increases in the sensitivity of the microelectrodes for biogenic amines. These data support that Nafion-coated high temperature (200 degrees C) dried microelectrodes have enhanced recording properties as compared to microelectrodes, which are coated with Nafion and dried at 85 degrees C. In addition, high-speed chronoamperometric recordings of biogenic amines are not affected by solution changes in divalent cations (Ca(2+) or Mg(2+)).

Contribution of the hyperpolarization-activated current (I(h)) to membrane potential and GABA release in hippocampal interneurons.

Intrinsic GABAergic interneurons provide inhibitory input to the principal neurons of the hippocampus. The majority of interneurons located in stratum oriens (s.o.) of the CA1 region express the hyperpolarization-activated cation current known as I(h). In an effort to elucidate the role of this current in regulating the baseline excitability of these neurons and its participation in the regulation of the release of GABA onto CA1 pyramidal neurons, we utilized whole cell electrophysiological recordings from both populations of cells. In voltage-clamp experiments, hyperpolarization of the interneuron membrane initiated a large inward current with an estimated activation threshold of 51.6 +/- 7.6 mV and a half-maximal voltage of -73.0 +/- 7.0 mV. This current was blocked by bath application of the I(h) inhibitors ZD 7288 (50 microM) or cesium (2 mM). Current-clamp experiments at the interneuron resting membrane potential (-61.3 +/- 1.2 mV) revealed a significant hyperpolarization, a decrease in the rate of spontaneous action potential discharge, an increase in the cellular input resistance, and the elimination of rebound afterdepolarizations during blockade of I(h) with ZD 7288 (50 microM). The hyperpolarizing effect of ZD 7288 was also substantially larger in interneurons clamped near -80 mV using current injection through the pipette. In addition to neurons exhibiting I(h), recordings were obtained from a small population of s.o. interneurons that did not exhibit this current. These cells demonstrated resting membrane potentials that were significantly more negative (-73.6 +/- 5.5 mV) than those observed in neurons expressing I(h), suggesting that this current contributes to more depolarized membrane potentials in these cells. Recordings from postsynaptic pyramidal neurons demonstrated that blockade of I(h) with ZD 7288 caused a substantial reduction (approximately 43%) in the frequency of spontaneous action potential-dependent inhibitory postsynaptic currents (IPSCs), without altering their average amplitude. However, miniature action-potential-independent IPSC frequency, amplitude, and decay kinetics were unaltered by ZD 7288. These data suggest that I(h) is active at the resting membrane potential in s.o. interneurons and as a result contributes to the spontaneous activity of these cells and to the tonic inhibition of CA1 pyramidal neurons in the hippocampus.

Direct actions of cannabinoids on synaptic transmission in the nucleus accumbens: a comparison with opioids.

The nucleus accumbens (NAc) represents a critical site for the rewarding and addictive properties of several classes of abused drugs. The medium spiny GABAergic projection neurons (MSNs) in the NAc receive innervation from intrinsic GABAergic interneurons and glutamatergic innervation from extrinsic sources. Both GABA and glutamate release onto MSNs are inhibited by drugs of abuse, suggesting that this action may contribute to their rewarding properties. To investigate the actions of cannabinoids in the NAc, we performed whole cell recordings from MSNs located in the shell region in rat brain slices. The cannabinoid agonist WIN 55,212-2 (1 microM) had no effect on the resting membrane potential, input resistance, or whole cell conductance, suggesting no direct postsynaptic effects. Evoked glutamatergic excitatory postsynaptic currents (EPSCs) were inhibited to a much greater extent by [Tyr-D-Ala(2), N-CH(3)-Phe(4), Gly-ol-enkephalin] (DAMGO, approximately 35%) than by WIN 55,212-2 (<20%), and an analysis of miniature EPSCs suggested that the effects of DAMGO were presynaptic, whereas those of WIN 55,212-2 were postsynaptic. However, electrically evoked GABAergic inhibitory postsynaptic currents (evIPSCs), were reduced by WIN 55,212-2 in every neuron tested (EC(50) = 123 nM; 60% maximal inhibition), and the inhibition of IPSCs by WIN 55,212-2 was completely antagonized by the CB1 receptor antagonist SR141716A (1 microM). In contrast evIPSCs were inhibited in approximately 50% of MSNs by the mu/delta opioid agonist D-Ala(2)-methionine(2)-enkephalinamide and were completely unaffected by a selective mu-opioid receptor agonist (DAMGO). WIN 55,212-2 also increased paired-pulse facilitation of the evIPSCs and did not alter the amplitudes of tetrodotoxin-resistant miniature IPSCs, suggesting a presynaptic action. Taken together, these data suggest that cannabinoids and opioids differentially modulate inhibitory and excitatory synaptic transmission in the NAc and that the abuse liability of marijuana may be related to the direct actions of cannabinoids in this structure.

Mechanisms of cannabinoid inhibition of GABA(A) synaptic transmission in the hippocampus.

The localization of cannabinoid (CB) receptors to GABAergic interneurons in the hippocampus indicates that CBs may modulate GABAergic function and thereby mediate some of the disruptive effects of marijuana on spatial memory and sensory processing. To investigate the possible mechanisms through which CB receptors may modulate GABAergic neurotransmission in the hippocampus, whole-cell voltage-clamp recordings were performed on CA1 pyramidal neurons in rat brain slices. Stimulus-evoked GABA(A) receptor-mediated IPSCs were reduced in a concentration-dependent manner by the CB receptor agonist WIN 55,212-2 (EC(50) of 138 nM). This effect was blocked by the CB1 receptor antagonist SR141716A (1 microM) but not by the opioid antagonist naloxone. In contrast, evoked GABA(B)-mediated IPSCs were insensitive to the CB agonist. WIN 55,212-2 also reduced the frequency of spontaneous, action potential-dependent IPSCs (sIPSCs), without altering action potential-independent miniature IPSCs (mIPSCs), measured while sodium channels were blocked by tetrodotoxin (TTX). Blockade of voltage-dependent calcium channels (VDCCs) by cadmium also eliminated the effect of WIN 55,212-2 on sIPSCs. Depolarization of inhibitory terminals with elevated extracellular potassium caused a large increase in the frequency of mIPSCs that was inhibited by both cadmium and WIN 55,212-2. The presynaptic effect of WIN 55,212-2 was also investigated using the potassium channel blockers barium and 4-aminopyridine. Neither of these agents significantly altered the effect of WIN 55,212-2 on evoked IPSCs. Together, these data suggest that presynaptic CB1 receptors reduce GABA(A)- but not GABA(B)-mediated synaptic inhibition of CA1 pyramidal neurons by inhibiting VDCCs located on inhibitory nerve terminals.

Differences in pharmacological properties of dopamine release between the substantia nigra and striatum: an in vivo electrochemical study.

The properties of dopamine (DA) release in the rat substantia nigra (SN) and striatum were investigated using high-speed chronoamperometric recordings in brain slices. In both brain regions, a 2-min bath superfusion with 30 mM KCl produced robust DA-like electrochemical signals, with the mean amplitude of the signal being >10-fold greater in the striatum than the SN. The reproducibility of the response was confirmed by a second stimulus (S2)/first-stimulus (S1) ratio of >0.8 in both regions. The bath application of tetrodotoxin significantly reduced the S2/S1 ratio in both the striatum and SN, implicating the requirement for voltage-sensitive sodium channels in the DA-release process. However, the application of cadmium chloride, a nonselective blocker of voltage-sensitive calcium channels, reduced the S2/S1 ratio only in the striatum and not within the SN. Moreover, removal of Ca2+ from the buffer did not significantly affect release within the SN, despite a >85% reduction in release within the striatum. In addition, although the D2 receptor antagonist sulpiride enhanced the S2/S1 ratio in the striatum, no effect of this agent was seen in the SN. Finally, the application of d-amphetamine produced DA-like electrochemical signals in both the striatum and SN. However, the amplitude of the d-amphetamine-evoked response, relative to the KCl-evoked release, was much smaller in the striatum than in the SN. Taken together, these data support the hypothesis that differences in the mechanism or mechanisms of release exist between somatodendritic and axonal elements within the nigrostriatal pathway.

Voltage-dependency of the dopamine transporter in the rat substantia nigra.

The possible voltage-dependence of the dopamine transporter (DAT) was investigated using electrophysiological and electrochemical recordings in rat brain slices containing the substantia nigra (SN). Whole-cell patch clamp recordings of DA neurons, revealed that addition of 15 mM KCl rapidly depolarized the membrane potential by approximately 20 mV, whereas these cells were hyperpolarized approximately 10 mV by DA (10 microM) and approximately 14 mV by the GABAB-receptor agonist baclofen (30 microM). High-speed chronoamperometric recordings were used to monitor clearance properties of exogenously applied DA signals during similar manipulations. Superfusion of slices with 15 mM KCl significantly increased the time course of the DA signal, consistent with inhibition of DAT activity. Application of the D2 DA-receptor antagonist sulpiride (50 microM) also significantly increased the time course, suggesting that DA-induced hyperpolarization enhances DAT activity. Baclofen reversed the effects of sulpiride on DA clearance. These results demonstrate that changes in DA cell membrane potential can modulate DAT activity.

Nicotine-evoked nitric oxide release in the rat hippocampal slice.

The effects of cholinergic agonists on nitric oxide (NO) release in hippocampal slices from male Sprague-Dawley rats were investigated using electrochemical recording procedures using Nafion and O-phenylenediamine-treated carbon fiber microelectrodes. These microelectrodes are highly selective for NO versus other interferents. Acetylcholine (Ach) with neostigmine, or nicotine was delivered by pressure ejection from pipettes placed within 300 microm of the NO sensors. Both Ach and nicotine produced NO signals ranging from 0.04 to 2.14 microM in the CA1, CA3, and dentate gyrus of the rat hippocampus that lasted for 2-5 min. The Ach responses were not antagonized by the muscarinic antagonist atropine. However, nicotine-evoked responses were partially antagonized by alpha-bungarotoxin, a finding consistent with alpha7-nicotinic cholinergic receptors being involved with the effects of nicotine. These data support the hypothesis that nicotine is capable of evoking long lasting NO release in the hippocampus.

Dopamine transporter activity in the substantia nigra and striatum assessed by high-speed chronoamperometric recordings in brain slices.

High-speed chronoamperometric measurements were used to measure clearance of locally applied dopamine (DA) in rat brain slices containing the substantia nigra (SN) or striatum. A comparison of DA signals of similar amplitudes between brain regions revealed that DA clearance was more rapid in the striatum than in the SN, consistent with the known greater distribution of the dopamine transporter (DAT) in the striatum. To clarify the role of the DAT in mediating DA clearance within the SN, slices were superfused with uptake inhibitors with different selectivities for the various monoamine transporters. In the SN, both cocaine and nomifensine significantly increased the amplitude and time course of the DA electrochemical signal. However, neither the serotonin transporter (SERT) inhibitor citalopram nor the norepinephrine transporter (NET) inhibitor desipramine (DMI) produced significant effects on DA clearance. In addition, cocaine and nomifensine affected the clearance parameters of the DA electrochemical signal to a similar extent in both the striatum and the SN, further confirming the functional role of the DAT in both brain regions. Local applications of d-amphetamine resulted in slow, prolonged DA-like electrochemical signals in both the SN and striatum, although the amplitude of the evoked response was larger within the striatum. In contrast, KCl-evoked depolarizations yielded rapid, detectable DA-like signals only within the striatum. Taken together, these data demonstrate the functional role of DAT in mediating DA clearance and release within both the striatum and SN.

In vivo electrochemical studies of dopamine clearance in the rat substantia nigra: effects of locally applied uptake inhibitors and unilateral 6-hydroxydopamine lesions.

High-speed chronoamperometric recordings were used to measure the uptake and clearance of locally applied dopamine (DA) within the substantia nigra (SN) of anesthetized rats. To establish that DA clearance within the SN was mediated primarily by the DA transporter (DAT) rather than the norepinephrine transporter (NET) or the serotonin transporter (SERT), we locally applied uptake inhibitors with different selectivity profiles for the various amine transporters. Nomifensine, a DAT/NET inhibitor, significantly potentiated both the amplitude and the time course of the DA signals. In contrast, neither the selective NET inhibitor desipramine, nor the selective SERT inhibitor citalopram affected the DA signal, suggesting that NET and SERT do not contribute to DA uptake and clearance within the regions of the SN studied over the concentration ranges (1-5 microM) used. In unilaterally 6-hydroxydopamine-lesioned rats, the time course of the DA signal was increased in both the lesioned SN and striatum, relative to the unlesioned hemisphere, indicating loss of DAT and decreased DA uptake and clearance. In addition, when identical amounts of DA were injected in the striatum and SN, peak signal amplitudes were larger in the SN, suggesting that the amplitudes are related to the number of DAT sites in a given region of brain tissue. For signals of equivalent amplitudes, clearance rates were lower in the SN than in the striatum, consistent with a lower capacity for DAT-mediated DA uptake within the SN. These results suggest that the DAT is the major transporter responsible for DA clearance within the rat SN.

In vivo microdialysis studies on somatodendritic dopamine release in the rat substantia nigra: effects of unilateral 6-OHDA lesions and GDNF.

Dopamine (DA) release and metabolism within the substantia nigra (SN) were studied in normal rats, rats with unilateral 6-hydroxydopamine (6-OHDA) lesions, and 6-OHDA-lesioned rats treated with glial cells line-derived neurotrophic factor (GDNF). Animals with > 99% DA depletions, as determined by apomorphine-induced circling behavior, also showed significant deficits in several measures of spontaneous motor activity. In vivo microdialysis recordings in the SN were carried out in normal and unilaterally 6-OHDA-lesioned rats. Basal levels of DNA were detectable only in the dialysates of normal animals, and basal levels of t he primary DA metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were found to be significantly reduced in the SN of 6-OHDA-lesioned animals. In the presence of d-amphetamine, either alone or in combination with potassium, significant reductions in DA release were observed in the SN of 6-OHDA-lesioned animals compared to normal animals. Potassium-evoked DA release alone was not significantly different between the groups. A single intranigral administration of GDNF into 6-OHDA-lesioned animals elicited a significant reduction in apomorphine-induced rotation behavior and a significant increase in spontaneous motor activities. These behavioral changes were apparent at 1 week and persisted through 4 weeks following treatment. In vivo microdialysis showed that, although DA metabolism was altered 1 week following GDNF treatment, DA release was not significantly affected until 4 weeks following treatment.

Onychomycosis.

The prevalence and clinical types of onychomycosis and diagnostic methods are reviewed in this article. The need for correct identification of the causative organism is emphasized. The use of oral and topical therapeutic agents is outlined, with specific emphasis on relevant research data and potential side effects of these agents. Sections on the potential hazard of nail dust, onychomycosis in HIV-infected patients, and the long-term management of onychomycosis are also included.

Glial cell line-derived neurotrophic factor supports survival of injured midbrain dopaminergic neurons.

Glial cell-lined derived neurotrophic factor (GDNF) has been shown to promote survival of developing mesencephalic dopaminergic neurons in vitro. In order to determine if there is a positive effect of GDNF on injured adult midbrain dopaminergic neurons in situ, we have carried out experiments in which a single dose of GDNF was injected into the substantia nigra following a unilateral lesion of the nigrostriatal system. Rats were unilaterally lesioned by a single stereotaxic injection of 6-hydroxydopamine (6-OHDA; 9 micrograms/4 microliters normal saline with 0.02% ascorbate) into the medial forebrain bundle and tested weekly for apomorphine-induced (0.05 mg/kg s.c.) contralateral rotation behavior. Rats that manifested > 300 turns/hour received a nigral injection of 100 micrograms GDNF, or cytochrome C as a control, 4 weeks following the 6-OHDA lesion. Rotation behavior was quantified weekly for 5 weeks after GDNF. Rats were subsequently anesthetized, transcardially perfused, and processed for tyrosine hydroxylase immunohistochemistry. It was found that 100 micrograms GDNF decreased apomorphine-induced rotational behavior by more than 85%. Immunohistochemical studies revealed that tyrosine hydroxylase immunoreactivity was equally reduced in the striatum ipsilateral to the lesion in both cytochrome C and GDNF-injected animals. In contrast, large increments in tyrosine hydroxylase immunoreactivity were observed in the substantia nigra of animals treated with 100 micrograms of GDNF, with a significant increase in numbers of tyrosine hydroxylase-immunoreactive cell bodies and neurites as well as a small increase in the cell body area of these neurons. The results suggest that GDNF can maintain the dopaminergic neuronal phenotype in a number of nigral neurons following a unilateral nigrostriatal lesion in the rat.

Inhibition of lipid mediator biosynthesis in human inflammatory cells by BIRM 270.

BIRM 270 was developed as a potent and enantioselective inhibitor of LTB4 biosynthesis by human neutrophils, and was also found to inhibit LTC4 production by human eosinophils and lung mast cells. BIRM 270 inhibited LTB4 synthesis in neutrophils by preventing arachidonate release from membrane phospholipids, and over the same concentration range, inhibited PAF biosynthesis. BIRM 270 did not directly inhibit acylhydrolases which have been implicated in eicosanoid and PAF biosynthesis, suggesting an indirect mode of action.

BIRM 270: a novel inhibitor of arachidonate release that blocks leukotriene B4 and platelet-activating factor biosynthesis in human neutrophils.

(S)-N-[2-Cyclohexyl-1-(2-pyridinyl)ethyl]-5-methyl-2-benzoxazolamine+ ++ (BIRM 270) was identified as a potent and enantiomerically selective inhibitor of calcium ionophore A23187-stimulated leukotriene B4 biosynthesis in human neutrophils. The (S)- and (R)-enantiomers exhibited IC50 values of 1 nM and 40 nM, respectively. BIRM 270 did not inhibit 5-lipoxygenase activity in a cell-free assay. In addition, the compound did not interfere with the conversion of exogenous 5-lipoxygenase substrate (15S)-hydroperoxyeicosatetraenoic acid to (5S, 15S)-dihydroxyeicosatetraenoic acid in intact, ionophore-stimulated neutrophils. Under the same experimental conditions, BIRM 270 inhibited the production of 5-lipoxygenase products from endogenous substrate, suggesting that the compound affected arachidonate availability rather than metabolism. Consistent with this concept, the inhibition of leukotriene B4 biosynthesis by BIRM 270 was overcome by the addition of exogenous arachidonic acid to the leukocyte preparation. Direct measurement of free arachidonate by gas chromatography-mass spectrometry confirmed that BIRM 270 inhibited arachidonate release from ionophore-stimulated neutrophils. The compound did not affect arachidonate reacylation. The blockage of arachidonate release coincided with inhibition of leukotriene B4 biosynthesis in these cells. BIRM 270 also inhibited ionophore-stimulated platelet-activating factor biosynthesis by human neutrophils. Although these results suggest that BIRM 270 inhibited phospholipase A2-mediated deacylation of membrane phospholipids, the compound did not directly inhibit the high molecular weight, cytosolic phospholipase A2 derived from human neutrophils or U937 cells. Thus, suppression of arachidonate mobilization by BIRM 270 may be due to indirect inhibition of intracellular phospholipase A2 or to inhibition of another acylhydrolase activity.

Chronic treatment with levodopa and/or selegiline does not affect behavioral recovery induced by fetal ventral mesencephalic grafts in unilaterally 6-hydroxydopamine-lesioned rats.

It has been suggested that levodopa (L-dopa), a dopamine precursor used to treat Parkinson's disease, may be toxic to grafted fetal neuroblasts; if so, the use of the monoamine oxidase B inhibitor selegiline might prevent such toxicity. We randomly assigned 30 unilaterally 6-hydroxydopamine-lesioned male Sprague-Dawley rats, whose lesions were verified with low-dose apomorphine-induced rotations, to one of five treatment groups: (i) L-dopa methyl ester (125 mg/kg/day) with benserazide (a peripheral decarboxylase inhibitor; 25 mg/kg/day), (ii) L-dopa methyl ester with benserazide and selegiline (L-deprenyl; 0.5 mg/kg/day), (iii) selegiline only, (iv) and (v) vehicle (ascorbate in normal saline) only. After 2 weeks of twice-daily ip injections, the rats received fetal ventral mesencephalic grafts into the lesioned striatum; one vehicle group received sham grafts. Drug therapy was continued for 2 1/2 months post grafting. At 1 month after grafting, and every 2 weeks thereafter, the rats were tested using low-dose apomorphine-induced rotation. A 70% decrease in rotations among all grafted groups, relative to the shams, was found. No statistical differences among groups receiving various drug therapies were seen in behavior or in counts or dimensions of tyrosine hydroxylase-positive cells. We therefore conclude that, in the unilaterally lesioned rat model of Parkinson's disease, there is no adverse effect of L-dopa nor any significant effect of selegiline, either alone or coadministered with L-dopa, on behavioral recovery induced by fetal ventral mesencephalic grafts.

Evaluation of arterial blood flow in the lower extremity.

Podiatrists need to evaluate arterial blood flow to determine whether arterial flow is compatible for healing following a contemplated surgery, to determine whether arterial flow is at a compatible level to prevent tissue necrosis or heal an ischemic ulcer, and to determine whether the patient should be referred to a vascular surgeon for consideration of the possible surgery. This article addresses these needs and provides guidelines to help make these assessments.

Normal digital pressure changes following the postocclusive reactive hyperemia test.

The authors report digital pressure changes in normal subjects following the 5-min postocclusive reactive hyperemia test. This test increases the sensitivity of using toe pressures to assess the adequacy of blood flow.

Purification and characterization of a phospholipase A2 from human osteoarthritic synovial fluid.

Phospholipase A2 (PLA2) from human osteoarthritic synovial fluid was purified to homogeneity in three steps. The NH2-terminal amino acid sequence and biochemical characteristics of the enzyme were identical to the Peak A PLA2 activity of rheumatoid synovial fluid (1). The enzyme exhibited an apparent mass of 14,000, an absolute Ca+(+)-dependence, an alkaline pH optimum, and was inhibited by sodium deoxycholate (DOC), NaCl and 0.5 M Tris-HCl. The enzyme strongly preferred phosphatidylethanolamine (PE) as substrate over phosphatidylcholine (PC) or phosphatidylinositol (PI), and hydrolyzed PE containing arachidonic acid or linoleic acid in the sn-2 position at similar rates. Heparin bound to the enzyme but did not inhibit catalytic activity. In addition, the human enzyme was not inhibited by the acidic 'chaperone' subunit of crotoxin despite considerable sequence similarity with the basic PLA2 subunit of the neurotoxin. The enzyme was capable of hydrolyzing E. coli membrane phospholipids in the presence of the neutrophil bactericidal/permeability increasing protein (BPI). This finding, coupled to the reported pro-inflammatory activity and presence of the enzyme in inflammatory cells, supports the hypothesis that it may be a component of the host defense mechanism which can, under certain conditions, contribute to the pathogenesis of inflammatory disease.