Effects of primary alcohols on airway smooth muscle

BACKGROUND

The investigation examined whether primary alcohols could be used as tools to explore the mechanism of anesthetic actions in airway smooth muscle (ASM). The hypothesis was that, like volatile anesthetics, the primary alcohols relax intact ASM by decreasing intracellular Ca2+ concentration ([Ca2+]i) and by inhibiting agonist-induced increases in the force developed for a given [Ca2+]i (Ca2+ sensitivity).

METHOD

The effects of butanol, hexanol, and octanol on isometric force in canine tracheal smooth muscle were examined. The effects of hexanol on [Ca2+]i (measured with fura-2) and the relationship between force and [Ca2+]i were studied during membrane depolarization provided by KCl and during muscarinic stimulation provided by acetylcholine.

RESULTS

The primary alcohols relaxed ASM contracted by KCl or acetylcholine in a concentration-dependent manner, with potency increasing as chain length increased. The alcohols could completely relax the strips, even during maximal stimulation with 10 microM acetylcholine (median effective concentrations of 28 +/- 12, 1.3 +/- 0.4, and 0.14 +/- 0.05 mM [mean +/- SD] for butanol, hexanol, and octanol, respectively). Hexanol decreased both [Ca2+]i and force in a concentration-dependent manner. Hexanol decreased Ca2+ sensitivity during muscarinic stimulation but had no effect on the force-[Ca2+]i relationship in its absence.

CONCLUSIONS

Primary alcohols produce reversible, complete relaxation of ASM, with potency increasing as chain length increases, by decreasing [Ca2+]i and inhibiting increases in Ca2+ sensitivity produced by muscarinic receptor stimulation. These actions mimic those of volatile anesthetics on ASM, a circumstance suggesting that the primary alcohols may be useful tools for further exploring mechanisms of anesthetic effects on ASM.

Specific gap junctions enhance the neuronal vulnerability to brain traumatic injury

Traumatic brain injury results in neuronal loss and associated neurological deficits. Although most research on the factors leading to trauma-induced damage focuses on synaptic or ionic mechanisms, the possible role of direct intercellular communication via gap junctions has remained unexplored. Gap junctions connect directly the cytoplasms of coupled cells; hence, they offer a way to propagate stress signals from cell to cell. We investigated the contribution of gap junctional communication (GJC) to cell death using an in vitro trauma model. The impact injury, induced by a weight dropped on the distal CA1 area of organotypic hippocampal slices, results in glutamate-dependent cell loss. The gap junctional blockers carbenoxolone and octanol decreased significantly post-traumatic cell death, measured by propidium iodide staining over a 72 hr period after the impact. Dye coupling in the pyramidal layers was enhanced immediately after the injury and decreased over the following 24 hr. To determine whether specific connexins were involved in the spread of trauma-induced cell death, we used organotypic slices from connexin43 (Cx43) knock-out mice, as well as acute knock-outs by incubation with antisense oligodeoxynucleotides. Simultaneous knockdown of two neuronal connexins resulted in significant neuroprotection. Slices from the null-mutant Cx43 mice, as well as the acute Cx43 knockdown, also showed decreased cell death after the impact. The gap junctional blockers alleviated the trauma-induced impairment of synaptic function as measured by electrophysiological field potential recordings. These results indicate that GJC enhances the cellular vulnerability to traumatic injury. Hence, specific gap junctions could be a novel target to reduce injury and secondary damage to the brain and maximize recovery from trauma.

Inhibition of gap junction hemichannels by chloride channel blockers

Electrophysiological methods were used to assess the effect of chloride-channel blockers on the macroscopic and microscopic currents of mouse connexin50 (Cx50) and rat connexin46 (Cx46) hemichannels expressed in Xenopus laevis oocytes. Oocytes were voltage-clamped at -50 mV and hemichannel currents (ICx50 or ICx46) were activated by lowering the extracellular Ca2+ concentration ([Ca2+]o) from 5 mM to 10 microM. Ion-replacement experiments suggested that ICx50 is carried primarily (>95%) by monovalent cations (PK : PNa : PCl = 1.0 : 0.74 : 0.05). ICx50 was inhibited by 18beta-glycyrrhetinic acid (apparent Ki, 2 microM), gadolinium (3 microM), flufenamic acid (3 microM), niflumic acid (11 microM), NPPB (15 microM), diphenyl-2-carboxylate (26 microM), and octanol (177 microM). With the exception of octanol, niflumic acid, and diphenyl-2-carboxylate, the above agents also inhibited ICx46. Anthracene-9-carboxylate, furosemide, DIDS, SITS, IAA-94, and tamoxifen had no inhibitory effect on either ICx50 or ICx46. The kinetics of ICx50 inhibition were not altered at widely different [Ca2+]o (10-500 microM), suggesting that drug-hemichannel interaction does not involve the Ca2+ binding site. In excised membrane patches, application of flufenamic acid or octanol to the extracellular surface of Cx50 hemichannels reduced single channel-open probability without altering the single-channel conductance, but application to the cytoplasmic surface had no effect on the channels. We conclude that some chloride-channel blockers inhibit lens-connexin hemichannels by acting on a site accessible only from the extracellular space, and that drug-hemichannel interaction involves a high-affinity site other than the Ca2+ binding site.

Larviposition by nasopharyngeal bot fly parasites of Columbian black-tailed deer: a correction

Previous reports of Cephenemyia jellisoni Townsend (Diptera: Oestridae) larvipositing onto the lips/lower muzzle of deer, with larvae invading via the mouth, are shown to be erroneous. Additional studies with deer models baited with CO2, 1-octen-3-ol and Deer Trail Scent, and muzzle and nostrils treated with insect adhesive, revealed that only C. apicata Bennett & Sabrosky larviposited onto the lips/lower muzzle; C. jellisoni, by contrast, larviposited into the nostrils. Larval depositions were associated with females of both species observed attacking models. Females of both species also were found stuck on adhesive-treated, baited models not attended by observers. During several seasons of exposure, such models received 89 C. jellisoni larvipositions into the nostrils and 87 C. apicata larvipositions onto the lips/lower muzzle. In laboratory experiments nearly all larvae of both species remained stuck in adhesive within 1 mm or less of where they were deposited.

Prolonged epileptiform bursting induced by 0-Mg(2+) in rat hippocampal slices depends on gap junctional coupling

The transition from brief interictal to prolonged seizure, or 'ictal', activity is a crucial event in epilepsy. In vitro slice models can mimic many phenomena observed in the electroencephalogram of patients, including transition from interictal to ictaform or seizure-like activity. In field potential recordings, three discharge types can be distinguished: (1) primary discharges making up the typical interictal burst, (2) secondary bursts, lasting several hundred milliseconds, and (3) tertiary discharges lasting for seconds, constituting the ictal series of bursts. The roles of chemical synapses in these classes of burst have been explored in detail. Here we test the hypothesis that gap junctions are necessary for the generation of secondary bursts. In rat hippocampal slices, epileptiform activity was induced by exposure to 0-Mg(2+). Epileptiform discharges started in the CA3 subfield, and generally consisted of primary discharges followed by 4-13 secondary bursts. Three drugs that block gap junctions, halothane (5-10 mM), carbenoxolone (100 microM) and octanol (0.2-1.0 mM), abolished the secondary discharges, but left the primary bursts intact. The gap junction opener trimethylamine (10 mM) reversibly induced secondary and tertiary discharges. None of these agents altered intrinsic or synaptic properties of CA3 pyramidal cells at the doses used. Surgically isolating the CA3 subfield made secondary discharges disappear, and trimethylamine under these conditions was able to restore them.We conclude that gap junctions can contribute to the prolongation of epileptiform discharges.

A gap junctionally transmitted epithelial cell signal regulates endocytic yolk uptake in Oncopeltus fasciatus

For endocytic uptake of vitellogenins, developing oocytes of Oncopeltus require a soluble, diffusible molecular signal from their surrounding epithelial cells, and this signal must be transmitted through open gap junctions. Hormonal stimulation triggering synthesis and processing of vitellogenins into mature insect yolk spheres has been intensely studied, and follicle epithelial cells are known in several insects to contribute to the blood products which are endocytosed along with vitellogenins synthesized in the fat bodies. However, there has been little evidence that direct gap junctional communication is a requirement for endocytic activity by oocytes. In untreated control follicles, both electrical and dye coupling occur, and follicles incubated in vitro in physiological salt solution containing small amounts of blood and fluorescent dye produce fluorescently labeled nascent yolk spheres. Labeled yolk spheres were visible in both sectioned material, and, with (Laser) Confocal Scanning, in living material. Dye coupling was abolished by treatment with either 1 mM octanol, 0.5 mM ethyl methanesulfonate (EMS), or cytoplasmic acidification, with coupling coefficients also being affected as each of these gap junction antagonists down-regulated the connexons. With each of these treatments, after gap junctions were down-regulated, receptor-mediated endocytic uptake of blood-born vitellogenins came to a halt. Furthermore, Oncopeltus follicles with endocytic activity blocked in this manner could be rescued by microinjection of the soluble fraction of lysed epithelial cell cytoplasm, confirming that the process depended upon a molecular signal from the epithelial cells.

Smooth muscle cell response to mechanical injury involves intracellular calcium release and ERK1/ERK2 phosphorylation

We have investigated possible signaling pathways coupled to injury-induced ERK1/2 activation and the subsequent initiation of vascular rat smooth muscle cell migration and proliferation. Aortic smooth muscle cells were cultured to confluency and subjected to in vitro injury under serum-free conditions. In fluo-4-loaded cells, injury induced a rapid wave of intracellular Ca(2+) release that propagated about 200 microm in radius from the injured zone, reached a peak in about 20 s, and subsided to the baseline within 2 min. The wave was abolished by prior treatment with the sarcoplasmic reticulum ATPase inhibitor thapsigargin, but not by omission of extracellular Ca(2+). ERK1/2 activation reached a peak at 10 min after injury and was inhibited by the MEK1 inhibitor PD98059, as well as by thapsigargin, fluphenazine, genistein, and the Src inhibitor PP2. These inhibitors also reduced [(3)H]thymidine incorporation and migration of cells into the injured area determined at 48 h after injury. These results show that mechanical injury to vascular smooth muscle cells induces a Ca(2+) wave which is dependent on intracellular Ca(2+) release. Furthermore, the injury activates ERK1/2 phosphorylation as well as cell migration and replication.

Light, carbon dioxide, and octenol-baited mosquito trap and host-seeking activity evaluations for mosquitoes in a malarious area of the Republic of Korea

Two field trials for commercially available and experimental mosquito traps variously baited with light, carbon dioxide, octenol, or combinations of these were evaluated in a malarious area at Paekyeon-Ri near Tongil-Chon (village) and Camp Greaves, Paju County, Kyonggi Province, Republic of Korea. The host-seeking activity for common mosquito species was determined using hourly aspirator collections from a human- and propane lantern-baited Shannon trap. The total number of mosquitoes and number of each species captured during the test were compared using 8 x 8 and 5 x 5 Latin square designs based on trap location. Significant differences were observed for the total number of mosquitoes collected in the 8 x 8 test, such that counterflow geometry (CFG) with CO2 > or = CFG with CO2 and octenol > or = Shannon trap > or = Mosquito Magnet with octenol > American Biophysics Corporation (ABC) light trap with light, CO2 (500 ml/min), and octenol > or = ABC light trap with light and dry ice > or = ABC light trap with light and CO2 > ABC light trap with light only. A concurrent 5 x 5 test found significant differences in trap catch, where Mosquito Magnet with octenol > New Jersey light trap > or = EPAR Mosquito Killer with CO2 > or = ABC light trap with light and dry ice > Centers for Disease Control (CDC) light trap (manufactured by John W. Hock) with light and octenol. Significant differences in trap catch were noted for several species including: Aedes vexans, Anopheles sinensis, An. yatsushiroensis, An. lesteri, Culex pipiens, and Cx. orientalis. Traps baited with octenol captured significantly fewer Cx. pipiens than those not baited with octenol. Likewise, no Cx. orientalis were captured in octenol-baited traps. Host-seeking activity showed a similar bimodal pattern for all species captured. Results from these field trap evaluations can significantly enhance surveillance efforts. Significantly greater numbers of mosquitoes were captured with mosquito traps using counterflow technology (e.g., Mosquito Magnet and CFG traps) when compared to standard light and carbon dioxide-baited traps. Additionally, field evaluations demonstrate that various traps can be utilized for isolation and detection of arboviruses and other pathogens.

Functional expression and characterization of odorant receptors using the Semliki Forest virus system

The human olfactory system can recognize and discriminate a large number of different odorant molecules. The detection of chemically distinct odorants starts with the binding of an odorant ligand to a specific receptor protein on the olfactory neuron cell surface. To address the problem of olfactory perception at a molecular level, we have expressed and characterized different olfactory receptors with several expression systems. Here we provide the first documentation of functional expression of odorant receptors using the Semliki Forest virus system. The human odorant OR 17-40 receptor and the rat 17 receptor were functionally expressed in vertebrate kidney cells (HEK293) using recombinant Semliki Forest viruses. Receptors were expressed as a fusion protein with the N-terminal membrane import sequence of the guinea pig serotonin receptor. Experiments employing the Ca2+-sensitive dye fura-2 revealed a fast, transient increase in the [Ca2+]i after application of the specific agonists helional and octanal to HEK293 cells infected with viruses containing RNA for the human odorant OR 17-40 receptor and the rat 17 receptor, respectively.

Effective reduction of neuronal death by inhibiting gap junctional intercellular communication in a rodent model of global transient cerebral ischemia

Gap junctions assemble astrocytes into syncytia, allowing exchange of metabolites, catabolites, and second-messenger molecules. Connexin43 is the predominant connexin of astrocytic gap junctions. The distribution of gap junction protein connexin43 was analyzed in different subfields of the hippocampal formation as a function of time after transient forebrain ischemia. One decisive key step in understanding why an ischemic insult gradually expands may be to establish how gap junction channels permit dying cells in the ischemic focus to communicate, in particular, with viable cells. The role of gap junctional intercellular communication in the hippocampus under ischemic conditions could be decisive for cell death propagation. We found that the vulnerable CA1/CA2 subfields have a higher density of gap junctions than the resistant CA3/CA4 areas, that changes in the distribution of connexin43 immunoreactivity may correlate with the phenomenon of selective vulnerability, and that inhibition of astrocytic gap junction permeability by octanol restricts the flow of undesirable neurotoxins that could potentially exacerbate neuronal damage. This provides a novel perspective for analysis of the pathophysiology of cerebral ischemia.

Electrical coupling between glial cells in the rat retina

The strength of electrical coupling between retinal glial cells was quantified with simultaneous whole-cell current-clamp recordings from astrocyte-astrocyte, astrocyte-Müller cell, and Müller cell-Müller cell pairs in the acutely isolated rat retina. Experimental results were fit and space constants determined using a resistive model of the glial cell network that assumed a homogeneous two-dimensional glial syncytium. The effective space constant (the distance from the point of stimulation to where the voltage falls to 1/e) equaled 12.9, 6.2, and 3.7 microm, respectively for astrocyte-astrocyte, astrocyte-Müller cell, and Müller cell-Müller cell coupling. The addition of 1 mM Ba(2+) had little effect on network space constants, while 0.5 mM octanol shortened the space constants to 4.7, 4.4, and 2.6 microm for the three types of coupling. For a given distance separating cell pairs, the strength of coupling showed considerable variability. This variability in coupling strength was reproduced accurately by a second resistive model of the glial cell network (incorporating discrete astrocytes spaced at varying distances from each other), demonstrating that the variability was an intrinsic property of the glial cell network. Coupling between glial cells in the retina may permit the intercellular spread of ions and small molecules, including messengers mediating Ca(2+) wave propagation, but it is too weak to carry significant K(+) spatial buffer currents.

Field studies on efficacy of host odour baits for the biting midge Culicoides impunctatus in Scotland

The efficacy of some putative attractants for the biting midge Culicoides impunctatus (Goetghebuer) (Diptera: Ceratopogonidae) was assessed using odour-baited 'delta traps' and suction traps. 1-octen-3-ol was confirmed as a potent olfactory attractant for C. impunctatus when released at 0.06mg/h. Acetone (23mg/h) and a mix of six phenolic compounds (phenol, 3-ethylphenol, 4-ethylphenol, 3-methylphenol, 4-methylphenol and 4-propylphenol), at undetermined release rate, also significantly increased delta trap catches compared to unbaited controls. When tested in combination, there was evidence of synergism between CO2 (0.2L/min) and acetone, 1-octen-3-ol or cow urine, trap catches being, respectively, 4.7, 6.2 and 9.3-fold greater than for CO2 alone. Highest catches were obtained with triple bait combinations comprising cow urine + acetone + CO2 or cow urine + 1-octen-3-ol+CO2, which increased trap catches by X 22 and X 24, respectively, compared to CO2 alone. Culicoides impunctatus was found to be extremely sensitive to CO2 and responses, gauged over two field seasons, showed a significant dose-dependent increase in catch across the entire range of release rates (0.2-2.5 L/min). Responses to these release rates, ranging from small to large mammal equivalents, emphasized the important role of CO2 in host location by C. impunctatus. Uses of olfactory attractants for monitoring and control of Culicoides are reviewed on the basis of these results.

Spreading depolarization waves triggered by vagal stimulation in the embryonic chick brain: optical evidence for intercellular communication in the developing central nervous system

Throughout experiments on multiple-site voltage-sensitive dye recordings of neural activity in embryonic chick brain preparations, we have found a novel type of depolarization waves which spread widely from the brainstem to the whole brain region at a rapid rate (mm/s). This depolarization wave was triggered by glutamate-mediated postsynaptic potentials and was especially correlated to N-methyl-D-aspartate receptor function. Evidence that the spreading depolarization wave is eliminated by octanol or 18beta-glycyrrhetinic acid suggests that the depolarization wave depends on functions of gap junctions. The profile obtained with Ca(2+)-imaging experiments also suggests that the propagation of the depolarization wave is accompanied by a calcium wave. These results provide new evidence for intercellular functional communication between neural cells in the vertebrate central nervous system during embryonic development.

Direct inhibition of voltage-dependent Ca(2+) fluxes by ethanol and higher alcohols in rabbit T-tubule membranes

The effects of ethanol and higher alcohols on 45Ca(2+) fluxes, mediated by voltage-dependent Ca(2+) channels (VDCCs), were investigated in inside-out transverse (T)-tubule membrane vesicles from rabbit skeletal muscle. 45Ca(2+) effluxes were induced by membrane potentials generated via establishing K(+) gradients across the vesicles, and were significantly inhibited by the inorganic Ca(2+) channel blocker La(3+) (1 mM) and the Ca(2+) channel antagonist nifedipine (1-10 microM). Ethanol, in the concentration range of 100-400 mM, caused a significant suppression of depolarization-induced 45Ca(2+) fluxes. Ethanol also functionally modulated the effect of nifedipine (1-10 microM) and the Ca(2+) channel agonist Bay K 8644 (1 microM) on Ca(2+) effluxes. Pretreatment with pertussis toxin (5 microg/ml) or phorbol 12-myrstate 13-acetate (PMA, 50 nM) did not affect the ethanol inhibition of 45Ca(2+) fluxes. Further experiments with alcohols revealed that butanol, hexanol, octanol and decanol also significantly inhibited 45Ca(2+) effluxes. However, undecanol and dodecanol did not cause any significant change on 45Ca(2+) fluxes, indicating that the effects of alcohols on 45Ca(2+) effluxes exhibit a cut-off phenomenon. In radioligand binding studies, it was found that at the concentrations used in flux studies, alcohols did not alter the characteristics of the specific binding of [3H]PN 200-110 to T-tubule membranes. Results indicate that ethanol directly inhibits the function of voltage-dependent Ca(2+) channels without modulating the specific binding of Ca(2+) channel ligands of the dihydropyridine class, and that this inhibition is independent of intracellular Ca(2+) levels.

Optical recording of spreading depression in rat neocortical slices

A spreading depression (SD) was elicited in adult rat neocortical slices by microdrop application of high potassium and the SD propagation pattern was analyzed by recording simultaneously the extracellular DC potential and the changes in the intrinsic optical signal. The electrical SD with an average peak amplitude of 13.2+/-3.4 mV showed a good spatial and temporal correlation with the optical signal. In 79% of the slices, the SD was characterized by an initial increase of light reflectance by 2.3+/-1.6%, followed by a reflectance decrease of 0.5+/-2.4% and finally a larger and long-lasting increase by 5+/-2.4%. In the remaining slices, the SD revealed an initial decrease in light reflectance by 5.8+/-1.8% followed by an increase of 1.4+/-1.2%. In all slices, the recovery in the DC recording was faster as in the optical signal. The SD preferentially propagated within layers I-IV and could be blocked in most experiments by a vertical incision through upper layers or by local glutamate receptor blockade following microdrop application of kynurenic acid in layers II-III. The SD could be also blocked by bath application of kynurenic acid, MK-801 and octanol, but not by the more specific gap junction blocker carbenoxolone. Our results indicate that the high density of dendritic processes and glutamate receptors in layers II-IV promote the horizontal spread of the SD in these cortical layers and that gap junctions are not required for the propagation of SD in neocortical slices.

Carbenoxolone depresses spontaneous epileptiform activity in the CA1 region of rat hippocampal slices

An important contributor to the generation of epileptiform activity is the synchronization of burst firing in a group of neurons. The aim of this study was to investigate whether gap junctions are involved in this synchrony using an in vitro model of epileptiform activity. Hippocampal slices (400 microm) were prepared from female Sprague-Dawley rats (120-170 g). The perfusion of slices with a medium containing no added magnesium and 4-aminopyridine (50 microM) resulted in the generation of spontaneous bursts of population spikes of a fast frequency along with less frequent negative-going bursts. The frequency of the bursts produced was consistent over a 3h period. Carbenoxolone (100 microM), a gap junction blocker and mineralocorticoid agonist, perfused for 75 min, reduced the frequency of both types of spontaneous burst activity. Perfusion of spironolactone (1 microM), a mineralocorticosteroid antagonist, for 15 min prior to and during carbenoxolone perfusion did not alter the ability of carbenoxolone to depress the frequency of spontaneous activity. The incubation of hippocampal slices in carbenoxolone prior to recording increased the time taken for the spontaneous activity to start on change to the zero magnesium/4-aminopyridine medium and decreased the total number of spontaneous bursts over the first 60 min period. The ability of carbenoxolone to delay induction of epileptiform activity and reduce established epileptiform activity suggests that gap junctions contribute to the synchronization of neuronal firing in this model.

Increased dilator response to heptanol and octanol in aorta from DOCA-salt-hypertensive rats

This study tests the hypothesis that contractile responses in aortae of hypertensive rats are more dependent on gap junctional communication compared to those from normotensive rats. The experimental approach was pharmacological, using inhibitors of gap junctional activity (heptanol and octanol). Two models of experimental hypertension were characterized: (1) mineralocorticoid (DOCA)-hypertensive rats and (2) stroke-prone spontaneous hypertensive rats (SHRSP). Vessels from DOCA-hypertensive rats showed a greater relaxation to heptanol and octanol, particularly when precontracted with phenylephrine, compared to sham-operated animals. Octanol-induced relaxation in aortic segments from SHRSP did not differ from normotensive values regardless of the agonist used to cause contraction. These results suggest that in DOCA hypertension, gap junctional communication and voltage-operated calcium channels are differentially regulated, which could explain in part the changes in vascular reactivity observed in mineralocorticoid hypertension.

Electrical coupling and excitatory synaptic transmission between rhythmogenic respiratory neurons in the preBötzinger complex

Breathing pattern is postulated to be generated by brainstem neurons. However, determination of the underlying cellular mechanisms, and in particular the synaptic interactions between respiratory neurons, has been difficult. Here we used dual recordings from two distinct populations of brainstem respiratory neurons, hypoglossal (XII) motoneurons, and rhythmogenic (type-1) neurons in the preBötzinger complex (preBötC), the hypothesized site for respiratory rhythm generation, to determine whether electrical and chemical transmission is present. Using an in vitro brainstem slice preparation from newborn mice, we found that intracellularly recorded pairs of XII motoneurons and pairs of preBötC inspiratory type-1 neurons showed bidirectional electrical coupling. Coupling strength was low (<0.10), and the current that passed between two neurons was heavily filtered (corner frequency, <10 Hz). Dual recordings also demonstrated unidirectional excitatory chemical transmission (EPSPs of approximately 3 mV) between type-1 neurons. These data indicate that respiratory motor output from the brainstem involves gap junction-mediated current transfer between motoneurons. Furthermore, bidirectional electrical coupling and unidirectional excitatory chemical transmission are present between type-1 neurons in the preBötC and may be important for generation or modulation of breathing rhythm.

Activation of urocortin transport into brain by leptin

There are several transport systems for peptides and polypeptides at the blood-brain barrier (BBB) which facilitate the passage of bioactive substances from blood to brain or from brain to blood. Nonetheless, it would be a novel concept for one peptide or polypeptide to activate the transport of another peptide with a similar function but unrelated structure. In this study, we report the first observation of such a phenomenon: activation of a urocortin transport system at the BBB by leptin. Urocortin, a corticotropin-releasing factor (CRF)-related neuropeptide, is a more potent suppressor of food intake than leptin or CRF when injected peripherally. Radiolabeled urocortin ((125)I-urocortin) was used for these in vivo studies in mice; it remained stable and intact during the experimental period. Unlike CRF, urocortin was not saturably transported out of the brain. There was no substantial entry of (125)I-urocortin into brain as determined by sensitive multiple-time regression analysis after iv bolus injection. Addition of leptin, however, caused a dose-related increase in the influx of (125)I-urocortin and greatly facilitated its entry into brain parenchyma; this effect disappeared at higher doses of leptin. Moreover, in the presence of an activating dose of leptin, the entry of (125)I-urocortin into brain was saturable. The results indicate that the presence of leptin contributes to the potent satiety effects of urocortin after peripheral administration. Thus, the action of leptin in the periphery extends beyond its direct passage across the BBB and involves acute modulation of an inert transport system. We believe that these findings have broad physiological implications and indicate a unique function of the BBB as a regulatory interface.

A series of biotinylated tracers distinguishes three types of gap junction in retina

Gap junctions serve many important roles in various tissues, but their abundance and diversity in neurons is only beginning to be understood. The tracer Neurobiotin has revealed many different networks interconnected by gap junctions in retina. We compared the relative permeabilities of five different retinal gap junctions by measuring their permeabilities to a series of structurally related tracers. When large tracers were injected, the staining of coupled cells fell off more rapidly in some networks than others relative to Neurobiotin controls. Three distinctly different permeability profiles were found, suggesting that multiple neuronal connexin types were present. The most permeant to large molecules were gap junctions from A-type horizontal cells. The permeability of gap junctions of two types of amacrine cell were not distinguishable from those from B-type horizontal cells. The lowest permeability was found for gap junctions between cone bipolar cells and the AII amacrine cells to which they are coupled. Because only a single neural connexin type has been identified in retina, our results suggest more types remain to be found. To determine whether the unitary permeability of channels is altered by channel modulators, we reduced permeability with octanol and a cAMP analog. Although net permeability was substantially diminished, the proportion by which it declined was constant across tracer size. This suggests that these agents act only to close channels rather than alter individual channel permeabilities. This tracer series can therefore be used to contrast permeability properties of gap junctions in intact circuits, even at the level of individual channels.

Identification of sites of incorporation in the nicotinic acetylcholine receptor of a photoactivatible general anesthetic

Most general anesthetics including long chain aliphatic alcohols act as noncompetitive antagonists of the nicotinic acetylcholine receptor (nAChR). To locate the sites of interaction of a long chain alcohol with the Torpedo nAChR, we have used the photoactivatible alcohol 3-[(3)H]azioctanol, which inhibits the nAChR and photoincorporates into nAChR subunits. At 1 and 275 microm, 3-[(3)H]azioctanol photoincorporated into nAChR subunits with increased incorporation in the alpha-subunit in the desensitized state. The incorporation into the alpha-subunit was mapped to two large proteolytic fragments. One fragment of approximately 20 kDa (alpha V8-20), containing the M1, M2, and M3 transmembrane segments, showed enhanced incorporation in the presence of agonist whereas the other of approximately 10 kDa (alpha V8-10), containing the M4 transmembrane segment, did not show agonist-induced incorporation of label. Within alpha V8-20, the primary site of incorporation was alpha Glu-262 at the C-terminal end of alpha M2, labeled preferentially in the desensitized state. The incorporation at alpha Glu-262 approached saturation between 1 microm, with approximately 6% labeled, and 275 microm, with approximately 30% labeled. Low level incorporation was seen in residues at the agonist binding site and the protein-lipid interface at approximately 1% of the levels in alpha Glu-262. Therefore, the primary binding site of 3-azioctanol is within the ion channel with additional lower affinity interactions within the agonist binding site and at the protein-lipid interface.

Growth regulation of astrocytes and C6 cells by TGFbeta1: correlation with gap junctions

Transforming growth factor (TGF) beta1 enhanced in vitro [3H]thymidine incorporation into C6 cells and reduced that of astrocytes in the presence of a high serum concentration. It concomitantly raised the gap junction intercellular communication (GJIC) in normal astrocytes but reduced the coupling of C6 cells, and respectively increased or decreased the proportion of P2-phosphorylated connexin (Cx) 43 isoform in these cells. Finally, octanol, which inhibited GJIC in both cell types, increased the thymidine incorporation in C6 cells, but neither altered the proliferation of astrocytes nor their response to TGFbeta1. These data indicate that an inhibition of gap junction intercellular communication, due to an altered phosphorylation of connexin 43, may contribute to the proliferative response of C6 glioblastoma cells to TGFbeta1.

Responses of the biting midge Culicoides impunctatus to acetone, CO2 and 1-octen-3-ol in a wind tunnel

Responses of host-seeking female Culicoides impunctatus (Goetghebuer) (Diptera: Ceratopogonidae) to acetone, carbon dioxide and 1-octen-3-ol were measured in a wind tunnel. Carbon dioxide, presented as a filamentous plume, increased upwind flight in a dose-dependent manner, up to 0.09% concentration. A homogenous CO2 plume elicited similar upwind responses at concentrations up to 0.09%, whereas higher plume concentrations (> 0.1%) induced erratic responses with a suppression of upwind flight. Bovine equivalent concentrations of acetone (1.5 x 10(-6)g/l) and 1-octen-3-ol (1.3 x 10(-8)g/) failed to induce any significant upwind response when tested alone. In the presence of CO2, however, 1-octen-3-ol showed highly significant increases in upwind responses at concentrations of 1.3 x 10(-1) - 10(-8)g/l. Mixtures of CO2+ acetone also enhanced upwind flight at 1.5 x 10(-9)g/l. High tunnel concentrations of both 1-octen-3-ol and acetone inhibited upwind responses. These findings are discussed in relation to host finding by C. impunctatus and known mechanisms by which upwind flight is initiated and arrested at high odour concentrations.

Effects of gap junction blocker on vasopressin and vasoactive intestinal polypeptide rhythms in the rat suprachiasmatic nucleus in vitro

We examined effects of gap junction blockers, octanol and halothane, on circadian rhythms in the release of arginine-vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) in suprachiasmatic nucleus (SCN) slice cultures of the rat. Circadian rhythms in AVP and VIP release maintained when the SCN culture was treated with octanol for 42 h. However, the release of AVP and VIP showed no circadian rhythms after 7 days incubation with octanol or halothane. Circadian rhythmicity in the two peptide rhythms appeared after the removal of the drug from the culture medium. These findings suggested that the gap junction communication may be involved in intercellular coupling within each subpopulation of AVP or VIP neurons in the SCN.

pH Sensitivity of non-synaptic field bursts in the dentate gyrus

Under conditions of low [Ca(2+)](o) and high [K(+)](o), the rat dentate granule cell layer in vitro develops recurrent spontaneous prolonged field bursts that resemble an in vivo phenomenon called maximal dentate activation. To understand how pH changes in vivo might affect this phenomenon, the slices were exposed to different extracellular pH environments in vitro. The field bursts were highly sensitive to extracellular pH over the range 7.0-7.6 and were suppressed at low pH and enhanced at high pH. Granule cell resting membrane potential, action potentials, and postsynaptic potentials were not significantly altered by pH changes within the range that suppressed the bursts. The pH sensitivity of the bursts was not altered by pharmacologic blockade of N-methyl-D-aspartate (NMDA), non-NMDA, and GABA(A) receptors at concentrations of these agents sufficient to eliminate both spontaneous and evoked synaptic potentials. Gap junction patency is known to be sensitive to pH, and agents that block gap junctions, including octanol, oleamide, and carbenoxolone, blocked the prolonged field bursts in a manner similar to low pH. Perfusion with gap junction blockers or acidic pH suppressed field bursts but did not block spontaneous firing of single and multiple units, including burst firing. These data suggest that the pH sensitivity of seizures and epileptiform phenomena in vivo may be mediated in large part through mechanisms other than suppression of NMDA-mediated or other excitatory synaptic transmission. Alterations in electrotonic coupling via gap junctions, affecting field synchronization, may be one such process.