Influence of gangliosides or LPS-like gangliosides on the tumoricidal activity of adherent leukocytes

We previously showed that highly metastatic clones derived from the poorly metastatic human melanoma cell line M4Be are very radiosensitive provided that they are deficient in complex gangliosides. Here, we report that the highly metastatic clone 4 appears more sensitive to activated adherent leukocytes than M4Be via a transmembrane TNF-alpha-dependent mechanism. Adherent leukocytes (AL) were freshly isolated from different blood donors and were activated with Esherichia coli lipopolysaccharide (LPS). These AL contain 80% (73-93%) monocytes, 15% (6-20%) B lymphocytes and 5% (1-8%) T lymphocytes. The tumour cell survival following contact with AL was estimated with a clonogenic assay where isolated tumour cells were plated for 14 days with AL. We show on the one hand that either exogenous bovine brain GM1 gangliosides or Campylobacter jejuni LPS with GM1-like structure (LPS-like GM1) significantly decrease the hypersensitivity of clone 4 to AL. On the other hand, the cleaving with neuraminidase of more than 50% of the sialic residues bound to endogenous gangliosides in resistant M4Be cells significantly increases their sensitivity to AL. Thus, our highly metastatic cells appear both very sensitive to activated AL when they are deficient in complex gangliosides and resistant to AL when they are transiently exposed to exogenous gangliosides or LPS-like gangliosides. These in vitro data may reflect the paradoxidal behaviour of highly metastatic cells in vivo which appear both very sensitive to physiological stresses and able to survive to form secondary tumours.     

Mechanism of accumulation of prion amyloid in the CNS in experimental amyotrophic leukospongiosis]

The mechanism of accumulation of prion amyloid in guinea pig CNS in experimental slow virus disease--amyotrophic leuco-spongiosis (AL) was studied. The complex histochemical, immuno-cytochemical and ultrastructural studies revealed specific amyloid deposits in a few brain capillaries and in most of pia matter vessels. Taking into account the high AL agent titer in spleen throughout the disease period, conclusion was drawn of entering AL agent in CNS through blood-liquor barrier and blood-brain barrier. It was supposed that primary immune system damaging took place in AL pathogenesis.     

Interaction between geminivirus replication protein and the SUMO-conjugating enzyme is required for viral infection

Geminiviruses are small DNA viruses that replicate in nuclei of infected plant cells by using plant DNA polymerases. These viruses encode a protein designated AL1, Rep, or AC1 that is essential for viral replication. AL1 is an oligomeric protein that binds to double-stranded DNA, catalyzes the cleavage and ligation of single-stranded DNA, and induces the accumulation of host replication machinery. It also interacts with several host proteins, including the cell cycle regulator retinoblastoma-related protein (RBR), the DNA replication protein PCNA (proliferating cellular nuclear antigen), and the sumoylation enzyme that conjugates SUMO to target proteins (SUMO-conjugating enzyme [SCE1]). The SCE1-binding motif was mapped by deletion to a region encompassing AL1 amino acids 85 to 114. Alanine mutagenesis of lysine residues in the binding region either reduced or eliminated the interaction with SCE1, but no defects were observed for other AL1 functions, such as oligomerization, DNA binding, DNA cleavage, and interaction with AL3 or RBR. The lysine mutations reduced or abolished virus infectivity in plants and viral DNA accumulation in transient-replication assays, suggesting that the AL1-SCE1 interaction is required for viral DNA replication. Ectopic AL1 expression did not result in broad changes in the sumoylation pattern of plant cells, but specific changes were detected, indicating that AL1 modifies the sumoylation state of selected host proteins. These results established the importance of AL1-SCE1 interactions during geminivirus infection of plants and suggested that AL1 alters the sumoylation of selected host factors to create an environment suitable for viral infection.     

Molecular forms of alpha-melanocyte-stimulating hormone in the canine pituitary anterior and intermediate lobe.

Reverse-phase high pressure liquid chromatography (HPLC) and radioimmunoassay (RIA) were used to determine the distribution of naturally occurring forms of alpha-melanocyte-stimulating hormone (alpha-MSH) in acid extracts of pars intermedia (PI) and anterior lobe (AL) tissue from canine and rat pituitary. Similarly, intracellular and secreted forms of alpha-MSH were determined using cultured canine PI and AL cells. Rat PI tissue contained predominantly diacetyl-alpha-MSH, while monoacetyl-alpha-MSH was the most abundant form in canine PI. In both canine and rat AL tissue extracts desacetyl-alpha-MSH was the major form of alpha-MSH. The profile of alpha-MSH contained in and secreted into culture medium by canine PI cells was found to be very similar to that in PI tissue extracts. The proportion of monoacetyl-alpha-MSH and diacetyl-alpha-MSH secreted by cultured canine AL cells and contained in extracts of AL cells in culture, however, was much higher than that in tissue extracts. These results indicate that in the dog, as in all other mammalian species studied, acetylated forms of alpha-MSH predominate in PI tissue, while nonacetylated alpha-MSH is the major form in AL tissue. It appears, however, that acetylation of alpha-MSH may occur in cultured canine AL cells, possibly as a result of the absence of factors that normally inhibit acetyltransferase in vivo or as a consequence of culture conditions.     

Sensitivity of human melanoma cells to adherent leukocytes depends on the ratio between them, the activation status of adherent leukocytes and the metastatic potential of tumor cells

 This study examined the interaction of the poorly metastatic human melanoma cell line M4Be and the highly metastatic clone 4 derived from M4Be, with respect to fresh adherent leukocytes (AL) isolated from 17 different healthy blood donors. These AL contained 80% (73%–93%) monocytes, 15% (6%–20%) B lymphocytes and 5% (1%–8%) T lymphocytes. The survival of these tumor cells against the stress exerted by these AL was estimated with a clonogenic assay where isolated tumor cells were co-cultured for 14 days in contact with AL and lipopolysaccharide (LPS). For a given blood donor, AL either stimulates or inhibits the colony formation of the tumor cells (T) depending on the AL/T ratio, the AL activation status and the metastatic potential of tumor cells. At low AL/T ratios (<10/1) in the presence of low (8 ng/ml) and trace (8 pg/ml) levels of LPS, hydrogen peroxide (H₂O₂) release is significantly reduced, and tumor cells significantly increase their colony formation; the feeder effect of AL is suggested to be due to low concentrations of soluble tumor necrosis factor-alpha (TNF-α). At high AL/T ratios (>10/1), whatever the characteristics of the blood donor, clone 4 is significantly more sensitive than M4Be to AL activated with medium containing low (8 ng/ml) or high (1,000 ng/ml) levels of LPS; this killing effect is suggested to be due to TNF-α, both soluble and membrane-bound, but not to be due to release of H₂O₂. These data suggest that the regulatory role of AL, which remove the majority of human melanoma cells and stimulate the colony formation of a small fraction of them, is partly due to TNF-α. Received: 2 November 2000 / Accepted: 15 February 2001     

Effects of arginine/lysine supplementation and resistance training on glucose tolerance.

The purpose of this study was to evaluate and compare the effects of arginine/lysine supplementation (AL) and resistance training (RT) on changes in glucose tolerance and to determine whether alterations were associated with changes in selected hormonal parameters. The study involved 30 physically active college males, ages 20-30 yr, randomly assigned to one of four groups: placebo/control (P/C, n = 7), P/RT (n = 8), AL/C (n = 7), or AL/RT (n = 8). An AL supplement at a daily morning dose of 132 mg/kg fat-free body mass or placebo was administered orally to controls and training groups. During the 10-wk program, exercise subjects participated in a progressive resistance training program stressing all major muscle groups. Three-hour oral glucose tolerance (OGT) tests were performed on each subject before and after the 10-wk intervention to evaluate resting levels and responses of glucose, insulin, and glucagon. OGT parameters did not significantly change after intervention. It was concluded that neither AL supplementation nor RT had a significant effect on OGT.     

Cellular and molecular effects of unoprostone as a BK channel activator

Effects of unoprostone isopropyl (unoprostone), a prostaglandin metabolite analog; latanoprost, a PGF(2alpha) analog; and PGF(2alpha) were examined in HCN-1A cells, a model system for studies of large conductance Ca(2+) activated K(+)(BK) channel activator-based neuroprotective agents. Unoprostone and latanoprost, both used as anti-glaucoma agents, have been suggested to act through FP receptors and have neuroprotective effects. Ion channel activation, plasma membrane polarization, [Ca(2+)](i) changes and protection against long-term irreversible glutamate-induced [Ca(2+)](i) increases were studied. Unoprostone activated iberiotoxin (IbTX)-sensitive BK channels in HCN-1A cells with an EC(50) of 0.6+/-0.2 nM and had no effect on Cl(-) currents. Unoprostone caused IbTX-sensitive plasma membrane hyperpolarization that was insensitive to AL8810, an FP receptor antagonist. In contrast, latanoprost and PGF(2alpha) activated a Cl(-) current sensitive to [Ca(2+)](i) chelation, tamoxifen and AL8810, and caused IbTX-insensitive, AL8810-sensitive membrane depolarization consistent with FP receptor-mediated Ca(2+) signaling Cl(-) current activation. Latanoprost and PGF(2alpha), but not unoprostone, increased [Ca(2+)](i). Unoprostone, PGF(2alpha) only partially, but not latanoprost protected HCN-1A cells against glutamate-induced Ca(2+) deregulation. These findings show that unoprostone has a distinctly different mechanism of action from latanoprost and PGF(2alpha). Whether unoprostone affects the BK channel directly or an unidentified signaling mechanism has not been determined.     

Fibronectin accelerates the growth and differentiation of ameloblast lineage cells in vitro.

During tooth development, the growth and differentiation of ameloblast lineage (AL) cells are regulated by epithelial-mesenchymal interactions. To examine the dynamic effects of components of the basement membrane, which is the extracellular matrix (ECM) lying between the epithelium and mesenchyme, we prepared AL cells from the epithelial layer sheet of mandibular incisors of postnatal day 7 rats and cultured them on plates coated with type IV collagen, laminin-1, or fibronectin. The growth of AL cells was supported by type IV collagen and fibronectin but not by laminin-1 in comparison with that on type I collagen as a reference. Clustering and differentiation of AL cells were observed on all matrices examined. AL cells showed normal growth and differentiation at low cell density on fibronectin but not on type I collagen. Furthermore, the population of cytokeratin 14-positive cells on fibronectin was lower than that on other ECM components, suggesting that fibronectin may be a modulator to accelerate the differentiation of AL cells. After the cells had been cultured for 9 days on fibronectin, crystal-like structures were observed. These structures overlaid the cell clusters and were positive for von Kossa staining. These findings indicate that each matrix component has a regulative role in the proliferation and differentiation of AL cells and that fibronectin causes the greatest acceleration of AL cell differentiation.     

Effect of capsaicin on voltage-gated currents of trigeminal neurones in cell culture and slice preparations

Effects of capsaicin on voltage-gated currents were examined in vitro by whole-cell patch-clamp recordings from small neurones of rat trigeminal ganglia either in slice preparations or in different cell cultures. Cells were classified as sensitive to capsaicin if they responded with inward current and/or conductance change to the agent in nanomolar concentration. Capsaicin (150 to 330 nM) in sensitive cells reduced the mixed inward current evoked by depolarizing step or ramp commands in all preparations. In cultured cells, the inward current was depressed to 32.78 +/- 26.42% (n = 27) of the control. Both the tetrodotoxin-sensitive and -resistant inward currents were affected. The data support the concept that capsaicin besides acting on VR-1 receptors inhibits also some voltage gated channels. In 34 cultured cells, capsaicin increased the slope conductance to 170.5 +/- 68%. Percentage of capsaicin sensitive cells observed in nerve growth factor-treated cultured cell populations was higher (77.8%) than in the two other preparations (14.3 or 38.8%). It is concluded that 1) depression of the voltage-gated currents may play an important role in the functional desensitization of the sensory receptors and in the analgesic effect induced by the agent and 2) cell body of sensory neurones under native condition seems less sensitive to capsaicin then that of cells cultured in the presence of nerve growth factor.     

Glucocorticoid inhibition of immunoreactive beta-endorphin release from the anterior lobe of the rat pituitary: in vitro and in vivo studies

Glucocorticoid control of pituitary beta-endorphin (beta-END) release was investigated in vitro and in vivo. Cultured cells of both rat anterior (AL) and neurointermediate (NIL) lobe released beta-END-like immunoreactivity (beta-END-LI) in response to epinephrine (10(-7) M); however, only the response of AL cells was prevented by corticosterone (10(-8)-10(-6) M) or dexamethasone (10(-9)-10(-7) M). Gel chromatographic analysis (Sephadex G-50) revealed that the major forms of beta-END-LI released by AL cells corresponded to beta-END and beta-lipotropin (beta-LPH) in molecular size, whereas virtually all of the immunoreactivity released by NIL cells resembled beta-END. In vivo administration of dexamethasone attenuated the stress-induced release of beta-END-LI in a dose- and time-related fashion, having a more pronounced effect on plasma levels of beta-END-LI corresponding to beta-LPH in molecular size. Metyrapone (100 mg/kg), an inhibitor of glucocorticoid synthesis, evoked a rapid (20-40 min) four- to sixfold increase in total plasma beta-END-LI and 75% of this rise was due to immunoreactivity resembling beta-LPH in size. This response was diminished by coadministration of either dexamethasone (0.05-1.25 mg/kg) or corticosterone (0.05-1.25 mg/kg) and completely prevented by 4-hr pretreatment with dexamethasone (50 micrograms/kg). The briskness of the plasma beta-END-LI response to acute changes in glucocorticoid status suggests that a "rapid" feedback mechanism operates in the physiologic control of pituitary beta-END-LI secretion. Moreover, the ability of glucocorticoids to selectively inhibit AL release of beta-END-LI in vitro and their pronounced effect on plasma levels of beta-END-LI resembling beta-LPH, a marker of AL secretion, together indicate that glucocorticoids exert a selective influence over the secretion of AL corticotrophs in vivo. This demonstration of differential regulation of the AL versus IL secretion of beta-END-LI in vivo most likely reflects a phenomena having biologic importance related to the different physiologic actions of the several molecular forms of beta-END-LI secreted by the two tissues.     

Annulate lamellae and single pore complexes in normal, SV40-transformed and tumor cells in vitro : A semiquantitative analysis

The frequency with which annulate lamellae (AL) and single cytoplasmic pore complexes appeared in selected groups (normal cell lines, SV40-, Rous sarcoma-, and 6/94 virus-infected cell lines, SV40-transformed cell lines, and both human and mouse tumor cell lines) was observed during standard electron microscopy techniques.All cell lines tested contained single pore complexes in the rough endoplasmic reticulum (RER). Further, it was found that at early passages WI38 cells have more single pore complexes than at later passages. In SV40-infected CV1 cells, the number of pore complexes increased during the infectious cycle, which indicates that the formation of these complexes may not be dependent on nuclear membrane remnants from mitosis. No pore complexes were found during mitosis, i.e., the formation of cytoplasmic pore complexes is by new synthesis or reformation. We speculate that all proliferating cells and germ cells generate pore complexes (similar to nuclear pore complexes) in their cytoplasmic membrane systems. With respect to annulate lamellae, it was found that:

1. (1) In cell lines where AL could be observed, not all cells exhibited AL stacks.

2. (2) “Normal” cells—such as human fetal lung (WI38) and monkey kidney (CV1) cells, mouse macrophages and fibroblasts, and cells from chicken explants—did not have AL stacks, but AL stacks could be induced by exposure to vinblastine.

3. (3) SV40-infected cells did not generate stacks of AL in the cell lines tested.

4. (4) SV40-transformed cells had AL stacks in a few cells or in many, depending on the cell line.

5. (5) The introduction of the SV40-containing chromosome 7 of human transformed LN-SV cells into a cell type that did not express AL formation caused it to form AL.

6. (6) AL were present up to 48 h after enucleation of mouse L cells, that is until the cells show signs of degeneration (which indicates that cellular upkeep of AL may not be dependent on the presence of the nucleus, as was suggested by the simultaneous disappearance of AL at mitosis).

7. (7) All tumor cell lines investigated were found to have AL stacks.

     

Treponemicidal activity of anti-treponemal lymphotoxins and their relation to circulating immune complexes and autolymphocytotoxins

Abstract It was previously reported that spleen cells of rabbits infected with Treponema pallidum produced anti-treponemal lymphotoxins (ATL). This ability was distinctly disturbed when circulating immune complexes (CIC) and autolymphocytotoxins (AL) were present in the sera of cell donors. ATL liberated from cells of donors without CIC and AL displayed a marked ability to immobilize treponemes. The percentage of immobilized treponemes varied according to the type of cells used for ATL liberation and their density. The most active was ATL from T cells (density 4 × 10⁸ ml⁻¹) and the weakest was the one from B lymphocytes. In the presence of CIC in sera of cell donors the weakest ATL was from macrophages and in the presence of AL from T lymphocytes. When both factors (CIC and AL) were present ATL from T lymphocytes did not immobilize treponemes. This seems to suggest that the impairment of the cells' ability to produce ATL may facilitate the survival of treponemes in the host despite the presence of immunologically competent cells.     

Molecular forms of α-melanocyte-stimulating hormone in the canine pituitary anterior and intermediate lobe

Reverse-phase high pressure liquid chromatography (HPLC) and radioimmunoassay (RIA) were used to determine the distribution of naturally occurring forms of α-melanocyte-stimulating hormone (α-MSH) in acid extracts of pars intermedia (PI) and anterior lobe (AL) tissue from canine and rat pituitary. Similarly, intracellular and secreted forms of α-MSH were determined using cultured canine PI and AL cells. Rat PI tissue contained predominantly diacetyl-α-MSH, while monoacetyl-α-MSH was the most abundant form in canine PI. In both canine and rat AL tissue extracts desacetyl-α-MSH was the major form of α-MSH. The profile of α-MSH contained in and secreted into culture medium by canine PI cells was found to be very similar to that in PI tissue extracts. The proportion of monoacetyl-α-MSH and diacetyl-α-MSH secreted by cultured canine AL cells and contained in extracts of AL cells in culture, however, was much higher than that in tissue extracts. These results indicate that in the dog, as in all other mammalian species studied, acetylated forms of α-MSH predominate in PI tissue, while nonacetylated α-MSH is the major form in AL tissue. It appears, however, that acetylation of α-MSH may occur in cultured canine AL cells, possibly as a result of the absence of factors that normally inhibit acetyltransferase in vivo or as a consequence of culture conditions.     

Multiple mitral leaflet contractile systems in the beating heart

Mitral valve closure may be aided by contraction of anterior leaflet (AL) cardiac myocytes located in the annular third of the leaflet. This contraction, observed as a stiffening of the annular region of the AL during isovolumic contraction (IVC), is abolished by beta-blockade (βB). Sub-threshold rapid pacing in the region of aorto-mitral continuity (STIM) also causes AL stiffening, although this increases the stiffness of the entire leaflet during both IVC and isovolumic relaxation (IVR). We investigated whether these contractile events share a common pathway or whether multiple AL contractile mechanisms may be present. Ten sheep had radiopaque-markers implanted: 13 silhouetting the LV, 16 on the mitral annulus, an array of 16 on the AL, and one on each papillary muscle tip. 4-D marker coordinates were obtained from biplane videofluoroscopy during control (C), βB (esmolol) and during βB+STIM. Circumferential and radial stiffness values for three AL regions (Annular, Belly, and free-Edge), were obtained from inverse finite element analysis of AL displacements in response to trans-leaflet pressure changes during IVC and IVR. βB+STIM increased stiffness values in all regions at both IVC and IVR by 35 ± 7% relative to βB (p<0.001). Thus, even when AL myocyte contraction was blocked by βB, STIM stiffened all regions of the AL during both IVC and IVR. This demonstrates the presence of at least two contractile systems in the AL; one being the AL annular cardiac muscle, involving a β-dependent pathway, others via a β-independent pathway, likely involving valvular interstitial cells and/or AL smooth muscle cells.     

In vitro and in vivo anti-allergic effects of Arctium lappa L

The discovery of drugs that can be used for the treatment of allergic disease is important in human health. Arctium lappa Linne (Compositae) (AL) has been used as a traditional medicine in Brazil and throughout Asia and is known to have an anti-inflammatory effect. In this study, the inhibitory effects of AL on degranulation and the release of mediators as well as on inhibition of cys-leukotriene biosynthesis by basophils were investigated. AL was selected out of 10,000 herbal extracts in a set-up for high throughput screening in which the degree of degranulation was monitored by the release of beta-hexosaminidase from rat basophil leukemia (RBL-2H3) cells. The AL extract significantly reduced degranulation and biosynthesis of cys-leukotrienes of human basophils in peripheral blood mono-nuclear cells (PBMCs) (50% inhibitory concentration [IC(50)] = 8.3 and 11.4 microg/ml, respectively). Viability and metabolic activity of the PBMCs were not affected. Although arctiin, the active component of AL that has been described in the literature, was not able to reduce degranulation in RBL-2H3 cells, a single high-performance liquid chromatography (HPLC) fraction from the AL extract inhibited beta-hexosaminidase release (IC(50) = 22.2 microg/ml). Topical administration of an aqueous extract of AL (5 mg/ear) on the ear of whey-sensitized mice 4 hrs before challenge with whey in the ear inhibited acute ear swelling by 50% in an in vivo cow's milk allergic model. The extract had no effect in this model when administered orally. In conclusion, the active component present in the active HPLC fraction of the AL extract was able to significantly reduce the release of inflammatory mediators through inhibition of degranulation and cys-leukotriene release in vitro. In addition, this active component was able to inhibit acute skin response in mice in vivo, indicating that AL is a very promising natural component for use in anti-allergic treatment.     

Factors that influence the development of cultured neurons from the brain of the mothManduca sexta

Summary During metamorphic adult development, neurons and glial cells in the developing olfactory (antennal) lobes of the moth undergo characteristic and extensive changes in shape. These changes depend on an interplay among these two cell types and ingrowing sensory axons. All of the direct cellular interactions occur against a background of changing steroid hormone titers. Antennal-lobe (AL) neurons dissociated from stage-5 (of 18 stages) metamorphosing animals survive at least 3 wk in primary cell culture. We describe here the morphological influences on AL neurons of (1) exposure to the steroid hormone 20-hydroxyecdysone, (2) exposure to sensory axons, and (3) interactions among the AL neurons. Cultured AL neurons respond only weakly, if at all, to 20-hydroxyecdysone. They do, however, show greater total outgrowth and branching when they had been exposed in vivo to sensory axons. Because there is no direct contact between some of the neuronal types and the sensory axons at the time of dissociation, the increase in outgrowth must have been mediated via a diffusible factor(s). When AL cells (neurons and glia) are plated at high density in low volumes of medium, or when the cells are plated at low density but in the presence of medium conditioned by high-density cultures, neurite outgrowth and cell survival are increased. Nerve growth factor (NGF), epidermal growth factor (EGF), fibroblast growth factor-basic (bFGF), transforming growth factor-β (TGF _β ) and insulin-like growth factor (ILGF) had no obvious effect on neuronal morphology and thus are unlikely to underlie these effects. Our results suggest that the mature shape of AL neurons depends on developmental interactions among a number of diffusible factors.     

Alkannin attenuates lipopolysaccharide‐induced lung injury in mice via Rho/ROCK/NF‐κB pathway

We investigated the effects and associated mechanism of alkannin (AL) on lipopolysaccharide (LPS)‐induced acute lung injury in a mouse model. Pretreatment with AL in vivo significantly reduced the lung wet/dry weight ratio and inhibited lung myeloperoxidase activity and malondialdehyde content, while increasing superoxide dismutase activity. Hematoxylin and eosin staining demonstrated that AL attenuated lung histopathological changes. In addition, AL‐inhibited overproduction of proinflammatory cytokines in bronchoalveolar lavage fluid and lung tissues in LPS‐injured mice and LPS‐exposed A549 cells. Further analysis showed that AL‐inhibited induction of the Rho/ROCK/NF‐κB pathway via LPS‐induced inflammation in mice and A549 cells. Fasudil, a selective ROCK inhibitor, showed similar effects. Overall, the findings indicate that AL suppresses the expression of messenger RNAs and proteins associated with Rho/ROCK/NF‐κB signaling to effectively ameliorate lung injury.     

LncRNA AL133467.1作为miR-661的ceRNA抑制乳腺癌细胞增殖和侵袭

长非编码RNAs((long non-coding RNAs,lncRNAs)在多种肿瘤中异常表达并参与肿瘤的发生发展.然而,众多lncRNAs在肿瘤的表达及功能尚未完全阐明.本文通过分析TCGT数据库113例正常乳腺组织和1109例乳腺癌组织发现,LneRNA AL133467.1在乳腺癌组织中低表达,并与乳腺癌患者...     

GABA-mediated synaptic inhibition of projection neurons in the antennal lobes of the sphinx moth,Manduca sexta

Responses of neurons in the antennal lobe (AL) of the moth Manduca sexta to stimulation of the ipsilateral antenna by odors consist of excitatory and inhibitory synaptic potentials. Stimulation of primary afferent fibers by electrical shock of the antennal nerve causes a characteristic IPSP-EPSP synaptic response in AL projection neurons. The IPSP in projection neurons reverses below the resting potential, is sensitive to changes in external and internal chloride concentration, and thus is apparently mediated by an increase in chloride conductance. The IPSP is reversibly blocked by 100 microM picrotoxin or bicuculline. Many AL neurons respond to application of GABA with a strong hyperpolarization and an inhibition of spontaneous spiking activity. GABA responses are associated with an increase in neuronal input conductance and a reversal potential below the resting potential. Application of GABA blocks inhibitory synaptic inputs and reduces or blocks excitatory inputs. EPSPs can be protected from depression by application of GABA. Muscimol, a GABA analog that mimics GABA responses at GABAA receptors but not at GABAB receptors in the vertebrate CNS, inhibits many AL neurons in the moth.