Internet use and its relationship to lonelines.

The association between Robert Weiss's bimodal theory of loneliness and Internet use was examined. The degree of social and emotional loneliness was assessed using the Social and Emotional Loneliness scale. This was compared with self-report measures of Internet use and the breadth of one's network of friends, both online and on a face-to-face basis. Low levels of social and emotional loneliness were both associated with high degrees of face-to-face networks of friends, while high levels of Internet use were associated with low levels of social loneliness and high levels of emotional loneliness. This supports recent research that has found that the Internet can decrease social well-being, even though it is often used as a communication tool.

Stereoselective actions of halothane at GABA(A) receptors.

Isoflurane anesthesia exhibits stereoselectivity, and a corresponding stereoselectivity ((+)->(-)-isomer) has been reported at GABA(A) receptors in vitro. The objective of the present study was to determine if the positive modulatory actions of halothane at GABA(A) receptors exhibited a similar stereoselectivity. Both (R)- and (S)-halothane ((+)- and (-)- isomers, respectively) enhanced [3H]flunitrazepam binding to brain membranes in a concentration dependent manner without a significant difference in either potency (EC50) or efficacy (Emax). While both (R)- and (S)-halothane enhanced [3H]muscimol binding, the potency of the (+)-isomer was slightly greater than the corresponding (-)-isomer (0.91 +/- 0.17 versus 1.45 +/- 0.04% atmospheres, respectively (P < 0.02)). Thus, subtle structural differences between inhalational anesthetics can have a significant impact on the degree of stereoselectivity at the receptor level and may provide insights for the development of more specific drugs.

Distinct structural requirements for the direct and indirect actions of the anaesthetic etomidate at GABA(A) receptors.

1. The intravenous anaesthetic etomidate augments GABA-gated chloride currents (indirect action) and, at higher concentrations, evokes chloride currents in the absence of GABA (direct action). 2. In order to identify amino acid residues essential for these actions, site directed mutagenesis was performed on the beta3 subunit. 3. Mutation of an asparagine to a serine residue at position 290 dramatically reduced both etomidate-induced chloride currents and its ability to enhance [3H]flunitrazepam binding in HEK293 cells expressing alpha1beta3gamma2 recombinant GABA(A) receptors. 4. In contrast, the indirect effect of etomidate was retained, though its potency was reduced. 5. These findings indicate that there are distinct requirements for these dual actions of etomidate at GABA(A) receptors.

Distinct loci mediate the direct and indirect actions of the anesthetic etomidate at GABA(A) receptors.

Most general anesthetics produce two distinct actions at GABA(A) receptors. Thus, these drugs augment GABA-gated chloride currents (referred to as an indirect action) and, at higher concentrations, elicit chloride currents in the absence of GABA (referred to as a direct action). Because a beta subunit appears to be required for the direct action of intravenous anesthetics in recombinant GABA(A) receptors, site-directed mutagenesis of the beta3 subunit was performed to identify amino acid residues that are critical for this action. In HEK293 cells expressing a prototypical GABA(A) receptor composed of alpha1beta3gamma2 subunits, mutation of amino acid 290 from Asn to Ser dramatically reduced both etomidate-induced chloride currents and its ability to stimulate [3H]flunitrazepam binding. By contrast, the ability of etomidate to augment GABA-gated chloride currents and GABA-enhanced [3H]flunitrazepam binding was retained. The demonstration that the direct, but not the indirect, actions of etomidate are dependent on beta3(Asn290) indicates that the dual actions of this intravenous anesthetic at GABA(A) receptors are mediated via distinct loci.

Contribution of "diazepam-insensitive" GABAA receptors to the alcohol antagonist properties of Ro 15-4513 and related imidazobenzodiazepines.

Both in vivo and in vitro studies have shown that Ro 15-4513 can antagonize many of the pharmacologic actions of ethanol. In contrast to many benzodiazepine receptor (BzR) ligands, Ro 15-4513 binds with high affinity to a novel GABAA receptor subtype, referred to as "diazepam-insensitive" (DI). This study examined the contribution of DI GABAA receptors to the modulation of ethanol-induced sleep time by Ro 15-4513 and related imidazobenzodiazepines [e.g., Ro 19-4603, Ro 16-6028, and ZG-63 (t-butyl-8-chloro-5,6-dihydro-5-methyl-6-oxo-imidazo[1,5,a] [1,4]benzodiazepine-3-carboxylate)] that possess high affinities for this GABAA receptor subtype. Ro 15-4513 (0.6-5 mg/kg) significantly reduced ethanol (3.5 g/kg, i.p.) sleep time in mice (p < 0.001, analysis of variance). This effect was not blocked by BzR antagonists ZK 93426 (5 mg/kg) and Ro 14-7437 (5 mg/kg), which possess low affinities for DI but bind with high affinities to other "diazepam-sensitive" (DS) GABAA receptor isoforms. Although Ro 19-4603 (2.5 mg/kg) also reduced ethanol sleep time (p < 0.01), this effect was attenuated by coadministration of ZK 93426 (2.5 mg/kg). Ro 16-6028 (2.5 mg/kg) prolonged (p < 0.01) ethanol sleep time. However, in the presence of either Ro 19-7437 (5 mg/kg) or ZK 93426 (2.5 mg/kg) ethanol-induced sleep time was reduced to values approaching those obtained with ethanol in the presence of Ro 15-4513. A low dose (2.5 mg/kg) of ZG-63 did not significantly affect alcohol sleep time. However, in the presence of ZK 93426, ZG-63 increased sleep time (p < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Different subunit requirements for volatile and nonvolatile anesthetics at gamma-aminobutyric acid type A receptors.

The ability of volatile (halothane and isoflurane) and nonvolatile (alphaxalone and pentobarbital) general anesthetics to modulate radioligand binding to gamma-aminobutyric acid (GABA)A receptors was examined in an immortalized cell line (WSS-1) expressing rat alpha 1 and gamma 2 subunits. Volatile anesthetics enhance [3H]flunitrazepam binding to WSS-1 cells in a concentration-dependent manner, with potencies and efficacies comparable to those found with native GABAA receptors. Transfection of these cells with cDNAs encoding rat beta 2 or beta 3 subunits had a significant influence on anesthetic efficacy but not potency in this assay. Thus, transfection with the beta 2 subunit reduced the efficacy of both isoflurane and halothane, whereas transfection with the beta 3 subunit increased the efficacy of isoflurane but not halothane, compared with values obtained in WSS-1 cells. In contrast, alpha-xalone (an anesthetic steroid) had no effect, whereas at high concentrations pentobarbital (an anesthetic barbiturate) produced a modest inhibition of [3H]flunitrazepam binding to GABAA receptors in WSS-1 cells. Transfection of WSS-1 cells with cDNAs encoding either beta 2 or beta 3 subunits resulted in a concentration-dependent enhancement of [3H]flunitrazepam binding by these nonvolatile anesthetics. Moreover, pentobarbital was significantly more potent in enhancing [3H]flunitrazepam binding to WSS-1 cells transfected with the beta 2 subunit, compared with the beta 3 subunit. The difference in subunit requirements between volatile and nonvolatile anesthetics for enhancement of [3H]flunitrazepam binding indicates that these classes of agents affect GABAA receptor function at distinct loci. These studies also provide evidence that the beta subunit is required for these nonvolatile anesthetics to positively modulate GABAA receptors.

The potential for safer anaesthesia using stereoselective anaesthetics.

The molecular mechanisms by which inhalational agents produce anaesthesia remains a subject of controversy, despite a history of clinical use spanning two centuries. The demonstration of a significant difference in the anaesthetic potencies of (+)- and (-)-isoflurane provides compelling evidence for the hypothesis that proteins, rather than lipids, are the primary sites of anaesthetic action. Moreover, the optically active isomers of volatile anaesthetics provide new tools to discriminate among putative molecular targets of anaesthesia. A difference in the anaesthetic potencies of (+)- and (-)-isoflurane, together with an apparent lack of stereoselectivity in their myocardial suppression, raises the possibility that an optically active volatile agent may have clinical advantages over currently available racemic mixtures.

Inhibition of [3H]isradipine binding to L-type calcium channels by the optical isomers of isoflurane. Lack of stereospecificity.

BACKGROUND: The dose-dependent myocardial depression of volatile general anesthetics such as isoflurane has been linked to blockade of L-type Ca2+ channels. The effects of (+)- and (-)-isoflurane on the inhibition of [3H]isradipine binding to L-type Ca2+ channels in membranes prepared from mouse heart were examined. In addition, because there is a stereo-specific effect of these isomers on sleep time in mice, the potential contribution of L-type Ca2+ channels to isoflurane-induced sleep was assessed by determining whether a similar stereoselectivity would be manifested at these sites in cerebral cortical membranes. METHODS: The effects of isoflurane stereoisomers on the binding of an L-type Ca2+ channel ligand ([3H]isradipine) were studied in cardiac and brain cortical membranes. Their potencies and effects on the Kd and Bmax of [3H]isradipine were measured. RESULTS: Pharmacologically relevant concentrations of (+)- and (-)-isoflurane inhibited [3H]isradipine binding. The IC50 values for (+)-isoflurane were 0.48 +/- 0.02% and 0.40 +/- 0.01% in heart and brain membranes, respectively. The values for (-)-isoflurane were not significantly different from the respective values for the (+)-isomer. Saturation analysis demonstrated (+)- and (-)-isoflurane inhibited [3H]isradipine binding by significantly reducing Bmax and increasing Kd, but there were no significant differences between these isomers in either tissue. CONCLUSIONS: The stereoisomers of isoflurane are equipotent as inhibitors of [3H]isradipine binding to L-type Ca2+ channels. This lack of stereoselectivity between (+)- and (-)-isoflurane indicates that the [3H]isradipine site on L-type Ca2+ channels in brain does not contribute to the differences in isoflurane-induced sleep time reported for these stereoisomers. Taken with a lack of stereoselectivity at L-type Ca2+ channels in heart, an optically resolved isomer of isoflurane may have clinical advantages compared to the current racemic mixture.

Volatile anesthetics bidirectionally and stereospecifically modulate ligand binding to GABA receptors.

Pharmacologically relevant concentrations of volatile anesthetics can bidirectionally modulate radioligand binding to GABAA receptors. In mouse cerebral cortex, halothane (a prototypic volatile anesthetic) increased [3H]muscimol (a GABA receptor agonist) binding while inhibiting the binding of a GABA receptor antagonist ([3H]SR 95531). These bidirectional effects of inhalational anesthetics on ligand binding to GABA receptors are effected through changes in the Bmax with no significant alterations in the KD of these radioligands. Moreover, the concentration dependent, bidirectional modulation of radioligand binding to GABA receptors by volatile anesthetics exhibited stereoselectivity. Thus, (+)-isoflurane was about twice as potent as the (-)-enantiomer in enhancing [3H]muscimol binding and approximately 50% more potent as an inhibitor of [3H]SR 95531 binding, respectively. The demonstration of a bidirectional, stereospecific modulation of radioligand binding to GABA receptors by inhalational agents is consistent with the presence of specific recognition sites for inhalational anesthetics on the GABAA receptor complex.

Stereospecific actions of the inhalation anesthetic isoflurane at the GABAA receptor complex.

The inhalation anesthetic isoflurane stereoselectively modulates ligand binding to the GABAA receptor complex. The (+)-isomer of isoflurane was more potent and efficacious than the (-)-isomer in enhancing [3H]flunitrazepam binding to benzodiazepine receptors. For example, concentration effect curves for Cl- enhancement of [3H]flunitrazepam binding were significantly different (P < 0.001) in the presence of (+)- and (-)-isoflurane (0.44 and 0.88 mM). At the higher anesthetic concentration, they potency of Cl- to increase [3H]flunitrazepam binding was increased 3.2- and 1.45-fold by (+)- and (-)-isoflurane, respectively (P < 0.05). Likewise, concentration-effect curves for (+) isoflurane-enhanced [3H]flunitrazepam binding were significantly different (P < 0.05-P < 0.001) from the (-)-isomer in the presence of 0-200 mM Cl-. Stereoselectivity was not observed with respect to the potencies of these enantiomers as inhibitors of [35S]t-butylbicyclophosphorothionate (TBPS) binding to sites within the Cl- ionophore. In this measure, the isomers had similar potencies (P > 0.05), although at higher concentrations (> 0.1 mM) (+)-isoflurane produced significantly more inhibition than (-)-isoflurane. While the absolute potency differences between isomers were modest (< or = 2-fold) and measure dependent, these effects were manifested at clinically relevant concentrations of isoflurane and are consistent with in vivo studies demonstrating (+)-isoflurane is a more effective anesthetic than the (-)-isomer. This is the first demonstration of an inhalation anesthetic producing a stereoselective perturbation of the GABAA receptor complex.

Site-specific acylation of GABA-gated Cl- channels: effects on 36Cl- uptake.

Radioligand binding studies indicate that p-isothiocyanato-t-butylbicycloorthobenzoate (p-NCS-TBOB) specifically acylates GABA-gated chloride channels. Preincubation of synaptoneurosomes with p-NCS-TBOB followed by washing resulted in a concentration dependent (63-500 nM) inhibition of both muscimol-stimulated chloride uptake and [355]t-butylbicyclophosphorothionate (TBPS) binding. The extent of acylation (assessed by inhibition of [35S]TBPS binding) was highly correlated (r = 0.89; p less than 0.001) with the inhibition of muscimol-stimulated Cl- uptake. Neither basal Cl- uptake nor [3H]muscimol binding to GABAA receptors were affected by p-NCS-TBOB. Preincubation with the nonacylating 'cage' convulsant t-butylbicycloorthobenzoate (500 nM) followed by washing had no effect on either muscimol-stimulated Cl- uptake or [35S]TBPS binding. These findings indicate that p-NCS-TBOB interferes with the efficacy of muscimol promoted channel openings, but does not affect the recognition qualities of GABAA receptors. p-NCS-TBOB should prove useful in electrophysiological and biochemical studies examining the properties of GABA-gated Cl- channels.

Ultraviolet irradiation selectively disrupts the gamma-aminobutyric acid/benzodiazepine receptor-linked chloride ionophore.

The ability of UV light to affect radioligand binding and 36Cl-uptake at the gamma-aminobutyric acidA (GABAA) receptor-chloride channel complex was examined. Exposure to 302 nm UV light produced a rapid (t1/2 = 4 min) reduction in [35S]t-butylbicyclo-phosphorothionate binding (assayed in the presence of 200 mM chloride) to sites associated with the GABAA receptor-coupled chloride ionophore. Saturation analysis revealed that this effect could be attributed entirely to a decrease in the maximum number of binding sites. Exposure to UV irradiation at lower (254 nm) and higher (366 nm) wavelengths also inhibited [35S]t-butylbicy-clophosphorothionate binding, but the respective rates of inactivation were 8- and 27-fold slower, compared with 302 nm. Other anion-dependent interactions at the GABAA receptor complex were disrupted in a similar manner. In the absence of permeant anion, [3H]flunitrazepam binding to benzodiazepine receptors was unaffected by 302 nm UV irradiation, whereas chloride-enhanced [3H]flunitrazepam binding was inhibited markedly. In the presence of 250-500 mM chloride, [3H]methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate binding to benzodiazepine receptors was also inhibited after UV exposure. Basal 36Cl- uptake into synaptoneurosomes was nearly doubled after 15 min of exposure to 302 nm light, whereas pentobarbital- and muscimol-stimulated 36Cl- uptake were reduced significantly. UV irradiation at 302 nm appears to disrupt selectively the anion-dependent functional interactions at the GABAA receptor complex. The apparent wavelength specificity suggests that the gating structure (channel) may contain tryptophan and/or tyrosine residues vital to the regulation of anion movement through the ionophore portion of this supramolecular receptor-ion channel complex.

Chlormethiazole: neurochemical actions at the gamma-aminobutyric acid receptor complex.

Chlormethiazole has been extensively employed as a sedative/hypnotic and anticonvulsant for more than 25 years. While pharmacological and electrophysiological studies have implicated the GABAA receptor complex in these actions, neurochemical findings have not been consistent with this conclusion. We now present evidence that pharmacologically relevant concentrations of chlormethiazole perturb the GABAA receptor complex. Chlormethiazole was found to increase 36Cl- uptake into rat cortical synaptoneurosomes in a concentration-dependent (EC50 = 48 +/- 3 microM; Emax = 8.9 +/- 0.8 nmol Cl-/mg protein per 5 s), picrotoxin-sensitive fashion. Chlormethiazole was also found to inhibit the binding of the 'cage' convulsant [35S]t-butylbicyclophosphorothionate to rat cortical membranes (IC50 = 58.6 +/- 0.6 microM) through an increase in the apparent KD of this radioligand. Moreover, at these concentrations chlormethiazole did not affect pentobarbital-enhanced [3H]flunitrazepam binding, but inhibited [3H]flunitrazepam binding with a low potency (IC50 = 1.6 +/- 0.2 mM). These findings provide neurochemical evidence that pharmacologically relevant concentrations of chlormethiazole can perturb the GABAA receptor complex, and suggest that this compound acts at a distinct locus from other sedative/hypnotics such as barbiturates, benzodiazepines and GABAmimetics.

Stereospecific reversal of nitrous oxide analgesia by naloxone.

The opiate antagonist naloxone was found to block nitrous oxide analgesia in a stereospecific fashion. Using a modified hotplate test in mice, the (-)-enantiomer of naloxone (which has a KD of approximately 1 nM for opiate receptors) antagonized the analgesic actions of nitrous oxide in a dose-dependent (2.5-20 mg/kg) fashion. In contrast, the (+)-enantiomer (KD approximately 10,000 nM) had no effect on nitrous oxide analgesia at the highest dose tested (40 mg/kg). These data strongly suggest that nitrous oxide analgesia is mediated via opiate receptors and is consistent with the hypotheses that this effect occurs either through the release of endogenous opioids or by physical perturbation of the opiate receptors.

Modulation of the benzodiazepine/gamma-aminobutyric acid receptor chloride channel complex by inhalation anesthetics.

Inhalation anesthetics, such as diethyl ether, halothane, and enflurane, increase 36Cl- uptake into rat cerebral cortical synaptoneurosomes in a concentration-dependent, picrotoxin-sensitive fashion. At concentrations consistent with those that stimulate 36Cl- uptake, inhalation anesthetics also inhibit the binding of t-[35S]butylbicyclophosphorothionate ([35S]TBPS) to well-washed cortical membranes. Scatchard analysis of [35S]TBPS binding indicates that these agents reduce the apparent affinity of this radioligand and have little effect on the Bmax. The ability of inhalation anesthetics to directly stimulate 36Cl- uptake and inhibit [35S]TBPS binding is a property shared by nonvolatile anesthetics. Nonetheless, there are differences between nonvolatile agents (such as barbiturates and alcohols) and inhalation anesthetics, because the former compounds augment muscimol (a GABAmimetic) stimulated 36Cl- uptake, whereas the latter group (such as ether and enflurane) inhibit this effect. These findings demonstrate that therapeutically relevant concentrations of inhalation anesthetics perturb the benzodiazepine/gamma-aminobutyric acid receptor chloride channel complex, and suggest this oligomeric protein may be a common mediator of some aspects of anesthetic action.

The imidazobenzodiazepine Ro 15-4513 antagonizes methoxyflurane anesthesia.

Parenteral administration of the imidazobenzodiazepine Ro 15-4513 (a high affinity ligand of the benzodiazepine receptor with partial inverse agonist qualities) produced a dose dependent reduction in sleep time of mice exposed to the inhalation anesthetic, methoxyflurane. The reductions in methoxyflurane sleep time ranged from approximately 20% at 4 mg/kg to approximately 38% at 32 mg/kg of Ro 15-4513. Co-administration of the benzodiazepine receptor antagonist Ro 15-1788 (16 mg/kg) or the inverse agonists DMCM (5-20 mg/kg) and FG 7142 (22.5 mg/kg) blocks this effect which suggests that the reductions in methoxyflurane sleep time produced by Ro 15-4513 are mediated via occupation of benzodiazepine receptors. Moreover, neither DMCM (5-20 mg/kg) nor FG 7142 (22.5 mg/kg) reduced methoxyflurane sleep time which suggests this effect of Ro 15-4513 cannot be attributed solely to its partial inverse agonist properties. These observations support recent findings that inhalation anesthetics may produce their depressant effects via perturbation of the benzodiazepine/GABA receptor chloride channel complex, and suggest that Ro 15-4513 may serve as a prototype of agents capable of antagonizing the depressant effects of inhalation anesthetics such as methoxyflurane.

Control of extracellular ions in skate brain during osmotic disturbances.

Regulation of brain water and osmolytes in osmotic disturbances has been studied in the little skate, Raja erinacea. Free-swimming fish were subjected to seawater plus 125 mM NaCl (hyperosmotic; these also received 10 ml/kg body wt im 4.19 M NaCl in elasmobranch Ringer) or to 50% seawater (hyposmotic). At a set time, fish were killed, and blood and brain (telencephalon and medulla) were analyzed. Brain water was divided into a Cl- and a non-Cl- space. Responses of water and osmolytes to osmotic disturbances were mutually consistent. In telencephalon, there was good regulation of Cl- space, based on Na+ and Cl- shifts in hypo- and hyperosmolality. This control was near perfect at 2- and 4-h hyperosmolality. Regulation of non-Cl- space was minimal at 24-h hyperosmolality, with small K+ uptake. In medulla, Cl- space and ions were unregulated, whereas non-Cl- space was partly controlled in hyposmolality in relation to amino acid loss. Thus in this elasmobranch, regulation of Cl- space and of Na+ and Cl- is effective in telencephalon but is nonexistent in medulla oblongata.

Sign language acquisition by a global aphasic.

A left hemisphere-damaged, hemiplegic, and globally aphasic man was taught receptive and expressive language using Total Communication--a combination of standardized sign language and speech. After an initial period during which words (in sign) were learned slowly and with frequent lapses of memory, the subject's learning ability and memory improved dramatically. He has learned to communicate using increasingly complex, syntactically correct sentences, self-correcting his mistakes. He reads and understands simple sentences. These results suggest that it may be possible to restore communicative function even in those stroke victims who remain orally aphasic if a suitable means of expression can be found.