Incidence of hyperoxia in trauma patients receiving pre-hospital emergency anaesthesia: results of a 5-year retrospective analysis

Background

Previous studies have demonstrated an association between hyperoxia and increased mortality in various patient groups. Critically unwell and injured patients are routinely given high concentration oxygen in the pre-hospital phase of care. We aim to investigate the incidence of hyperoxia in major trauma patients receiving pre-hospital emergency anesthesia (PHEA) in the pre-hospital setting and determine factors that may help guide clinicians with pre-hospital oxygen administration in these patients.

Methods

A retrospective cohort study was performed of all patients who received PHEA by a single helicopter emergency medical service (HEMS) between 1 October 2014 and 1 May 2019 and who were subsequently transferred to one major trauma centre (MTC). Patient and treatment factors were collected from the electronic patient records of the HEMS service and the MTC. Hyperoxia was defined as a PaO₂ > 16 kPA on the first arterial blood gas analysis upon arrival in the MTC.

Results

On arrival in the MTC, the majority of the patients (90/147, 61.2%) had severe hyperoxia, whereas 30 patients (20.4%) had mild hyperoxia and 26 patients (19.7%) had normoxia. Only 1 patient (0.7%) had hypoxia. The median PaO₂ on the first arterial blood gas analysis (ABGA) after HEMS handover was 36.7 [IQR 18.5–52.2] kPa, with a range of 7.0–86.0 kPa. SpO₂ pulse oximetry readings before handover were independently associated with the presence of hyperoxia. An SpO₂ ≥ 97% was associated with a significantly increased odds of hyperoxia (OR 3.99 [1.58–10.08]), and had a sensitivity of 86.7% [79.1–92.4], a specificity of 37.9% [20.7–57.8], a positive predictive value of 84.5% [70.2–87.9] and a negative predictive value of 42.3% [27.4–58.7] for the presence of hyperoxemia.

Conclusion

Trauma patients who have undergone PHEA often have profound hyperoxemia upon arrival at hospital. In the pre-hospital setting, where arterial blood gas analysis is not readily available a titrated approach to oxygen therapy should be considered to reduce the incidence of potentially harmful tissue hyperoxia.

Differential activation of the human costal and crural diaphragm during voluntary and involuntary breaths

Simultaneous electromyographic recordings from the human costal and crural diaphragm during voluntary augmented breathing and involuntary rebreathing show that the increase in inspiratory crural diaphragm activity was ~60% of the increase in costal diaphragm activity. However costal to crural diaphragm activation did not differ between the two tasks. The dissociation in the amplitude of activation of the costal and crural diaphragm becomes apparent only as the drive to breathe increases above tidal breathing.

Increased diaphragm motor unit discharge frequencies during quiet breathing in people with chronic tetraplegia

KEY POINTS

Respiratory muscle strength is compromised in people with tetraplegia, which may be compensated for by an increase in neural drive to the diaphragm. We found that the discharge frequencies of diaphragm motor units are higher in people with chronic tetraplegia compared with able-bodied people during quiet breathing. Furthermore, we found that the area of single motor unit potentials was increased in people with tetraplegia. These results suggest an increased motoneurone output to the diaphragm and remodelling of diaphragm motor units to maintain ventilation in tetraplegia.

ABSTRACT

People with tetraplegia have reduced inspiratory muscle strength, ∼40% of able-bodied individuals. Paralysed or partially paralysed respiratory muscles as a result of tetraplegia compromise lung function, increase the incidence of respiratory infections and can cause dyspnoea. We hypothesised that reduced inspiratory muscle strength in tetraplegia may increase neural drive to the inspiratory muscles to maintain ventilation. We recorded the discharge properties of single motor units from the diaphragm in participants with chronic tetraplegia (8 males, 42-78 years, C3-C6 injury, AIS A-C) and able-bodied control participants (6 males matched for age and body mass index). In each group, 117 and 166 single motor units, respectively, were discriminated from recordings in the costal diaphragm using a monopolar electrode. A linear mixed-effects model analysis showed higher peak discharge frequencies of motor units during quiet breathing in tetraplegia (17.8 ± 4.9 Hz; mean ± SD) compared with controls (12.4 ± 2.2 Hz) (P < 0.001). There were no differences in tidal volume, inspiratory time or mean air flow between groups. Motor unit potentials in tetraplegia, compared with controls, were larger in amplitude (1.1 ± 0.7 mV and 0.5 ± 0.3 mV, respectively, P = 0.007) and area (1.83 ± 1.49 µV ms and 0.69 ± 0.52 µV ms, respectively, P = 0.003). The findings indicate that diaphragm motor unit remodelling is likely to have occurred in people with chronic tetraplegia and that there is an increase in diaphragm motor unit discharge rates during quiet breathing. These neural changes ensure that ventilation is maintained in people with chronic tetraplegia.

Abdominal Functional Electrical Stimulation to Augment Respiratory Function in Spinal Cord Injury

Background: Functional electrical stimulation (FES) is the application of electrical pulses to a nerve to achieve a functional muscle contraction. Surface electrical stimulation of the nerves that innervate the abdominal muscles, termed abdominal FES, can cause the abdominal muscles to contract, even when paralysed after spinal cord injury. As the abdominal muscles are the major expiratory muscles, and commonly partially or completely paralysed in tetraplegia, abdominal FES offers a promising method of improving respiratory function for this patient group. Objective: The aim of the article is to provide readers with a better understanding of how abdominal FES can be used to improve the health of the spinal cord-injured population. Methods: A narrative review of the abdominal FES literature was performed. Results: Abdominal FES can achieve an immediate effective cough in patients with tetraplegia, while the repeated application over 6 weeks of abdominal FES can improve unassisted respiratory function. Ventilator duration and tracheostomy cannulation time can also be reduced with repeated abdominal FES. Conclusion: Abdominal FES is a noninvasive method to achieve functional improvements in cough and respiratory function in acute and chronically injured people with tetraplegia. Potential practical outcomes of this include reduced ventilation duration, assisted tracheostomy decannulation, and a reduction in respiratory complications. All of these outcomes can contribute to reduced morbidity and mortality, improved quality of life, and significant potential cost savings for local health care providers.

A Novel Gaba Receptor on Central Neurones

The features of γ-aminobutyric acid (GABA) as an inhibitory neurotransmitter are described, together with those of its receptor as defined by both iontophoretic and radiolabelled ligand binding techniques. Evidence is presented supporting the existence of a second GABA receptor at both peripheral nerve endings and within the CNS. At the classical receptor, GABA can produce a depolarisation of the ganglion cell body or mediate hyperpolarisation within the CNS by increasing membrane conductance to chloride ions. At this second receptor GABA acts in a bicuculline-insensitive manner to reduce neurotransmitter outflow.

Many GABA analogues active at the classical receptor are inactive at the second receptor but by contrast baclofen which is inactive at the classical receptor is a potent agonist at the novel site.

EVERSUN: a phase 2 trial of alternating sunitinib and everolimus as first-line therapy for advanced renal cell carcinoma

BACKGROUND

We hypothesised that alternating inhibitors of the vascular endothelial growth factor receptor (VEGFR) and mammalian target of rapamycin pathways would delay the development of resistance in advanced renal cell carcinoma (aRCC).

PATIENTS AND METHODS

A single-arm, two-stage, multicentre, phase 2 trial to determine the activity, feasibility, and safety of 12-week cycles of sunitinib 50 mg daily 4 weeks on / 2 weeks off, alternating with everolimus 10 mg daily for 5 weeks on / 1 week off, until disease progression or prohibitive toxicity in favourable or intermediate-risk aRCC. The primary end point was proportion alive and progression-free at 6 months (PFS6m). The secondary end points were feasibility, tumour response, overall survival (OS), and adverse events (AEs). The correlative objective was to assess biomarkers and correlate with clinical outcome.

RESULTS

We recruited 55 eligible participants from September 2010 to August 2012.

DEMOGRAPHICS

mean age 61, 71% male, favourable risk 16%, intermediate risk 84%. Cycle 2 commenced within 14 weeks for 80% of participants; 64% received ≥22 weeks of alternating therapy; 78% received ≥22 weeks of any treatment. PFS6m was 29/55 (53%; 95% confidence interval [CI] 40% to 66%). Tumour response rate was 7/55 (13%; 95% CI 4% to 22%, all partial responses). After median follow-up of 20 months, 47 of 55 (86%) had progressed with a median progression-free survival of 8 months (95% CI 5-10), and 30 of 55 (55%) had died with a median OS of 17 months (95% CI 12-undefined). AEs were consistent with those expected for each single agent. No convincing prognostic biomarkers were identified.

CONCLUSIONS

The EVERSUN regimen was feasible and safe, but its activity did not meet pre-specified values to warrant further research. This supports the current approach of continuing anti-VEGF therapy until progression or prohibitive toxicity before changing treatment.

AUSTRALIAN NEW ZEALAND CLINICAL TRIALS REGISTRY

ACTRN12609000643279.

Quetiapine and Buspirone Both Elevate Cortical Levels of Noradrenaline and Dopamine In vivo, but Do Not have Synergistic Effects

Decreased cognitive ability is a significant problem in schizophrenia, and it has been proposed that augmentation of antipsychotics with 5HT(1A) receptor agonists may improve cognitive performance. Clinical studies have been mixed but there have been no studies specifically examining the effects of combining the atypical antipsychotic quetiapine with the 5HT(1A) receptor partial agonist, buspirone on monoamine release. This is of interest given previous evidence that monoamine release can alter cognition in schizophrenia. In the present study we measured in vivo levels of monoamines in the frontal cortex of Sprague Dawley rats and examined if buspirone (2.5 mg/kg i.p.), altered monoamine release both when given alone and when combined with quetiapine (10 mg/kg i.p.). We found that serotonin levels were not altered by either drug, either alone or in combination. In contrast, both buspirone and quetiapine monotherapy significantly increased release of noradrenaline (112 and 160% respectively) and dopamine (169 and 191% respectively) compared to controls. However, there were no additional increases in in vivo monoamine release when the combination of these drugs were given. One possible explanation for these negative findings could be that the intrinsic 5HT(1A) agonist activity of quetiapine on its own is of such significance that it is not further enhanced by buspirone. These findings do not support clinical studies combining buspirone and quetiapine, if these were to be used on the basis of enhanced monoamine neurotransmission. These findings may also have implications for the atypical antipsychotic drugs in development which combine dopamine D(2) antagonism with 5HT(1A) partial agonism.

Symptom experience and functional status among HIV-infected women

Irrespective of powerful drug therapies, there has been a slight increase in newly diagnosed cases of AIDS in women. HIV/AIDS-related symptoms develop from the illness itself, treatments or medications. Symptoms and their reoccurrence remain problematic. This study is a secondary analysis of data exploring symptoms, symptom distress and functional status in 104 ethnically diverse HIV-positive women. Measures included the Brief Symptom Inventory, a General Symptom Questionnaire, the Center for Epidemiological Studies Depression Scale, and the Inventory of Functional Status. Findings indicate that this sample of women was distressed, at risk for depression and had a moderate level of physical functioning. These findings support the need for symptom management interventions that enhance emotional wellbeing and self-care activities for HIV-infected women.

Synthesis and biological activities of [7-(azetidine-2-carboxylic acid)]-oxytocin and -lysine-vasopressin

[7-(Azetidine-2-carboxylic acid)]-oxytocin and -lysine-vasopressin have been synthesised by a (6 + 3) strategy using protected hexapeptide acids with preformed disulphide bridges, and their biological activities have been investigated. All activities were reduced but not to the same extent. In assays of pressor and antidiuretic activity it was observed consistently that the responses to the vasopressin analogue were of shorter duration than responses to lysine-vasopressin of the same amplitude.

Pharmacological characterisation of the electrically evoked release of monoamines from chicken brainin vitro

1. A study was conducted to develop an in vitro model for examining the basal and electrical-stimulation-induced release of [3H]monoamines from chicken hyperstriatal neurones in order to demonstrate the presence of presynaptic autoreceptors for the three main monoamine transmitters: noradrenaline, dopamine and 5-HT. 2. Two sets of experiments were carried out: the first was to evaluate the effect of calcium and tetrodotoxin (TTX, sodium channel conductance inhibitor) in order to demonstrate that evoked release of monoamines was a consequence of exocytotic processes; the second to investigate the effect of selective agonists and antagonists on neurotransmitter release. 3. Ross and Cobb broiler chickens of either sex (approximately 7 to 8 weeks old) were used. Slices of hyperstriatal tissue were preincubated with [3H]noradrenaline, [3H]dopamine or [3H]5-hydroxytryptamine (5-HT), washed, perfused and electrically stimulated at three time points (S1, S2 and S3) which released [3H]noradrenaline, [3H]dopamine and [3H]5-HT, as determined by scintillation spectrometry. 4. When calcium was removed from, or TTX added to, the superfusion medium prior to and including the second period of electrical stimulation (S2) the evoked releases of [3H]noradrenaline, [3H]dopamine and [3H]5-HT at S2 were abolished. 5. In the presence of the selective alpha2-adrenoceptor agonist UK 14304 during the S2 period, the S2/S1 ratio was lower than the control ratio due to a reduction in the stimulated release of [3H]noradrenaline. The selective alpha2-adrenoceptor antagonist RX 821002 blocked the UK 14304-induced reduction of evoked release and the S2/S1 ratio was similar to the control ratio. 6. The D2-like receptor agonist quinpirole reduced the S2/S1 ratio for [3H]dopamine release, an effect blocked by the antagonist AJ 76. The 5-HT1B receptor agonist CP 94253 during S2 reduced the S2/S1 ratio due to a reduction in evoked [3H]5-HT. This effect was blocked by the 5-HT1B receptor antagonist GR 55562. 7. The results demonstrate, for the first time, the functional presence of presynaptic alpha2-adrenoceptors, presynaptic 5-HT1B autoreceptors and presynaptic D2-like autoreceptors in broiler chicken hyperstriatal neurones in vitro.

Invited review: the evolution of antidepressant mechanisms

Present antidepressants are all descendents of the serendipitous findings in the 1950s that the monoamine oxidase inhibitor iproniazid and the tricyclic antidepressant imipramine were effective antidepressants. The identification of their mechanism of action, and those of reserpine and amphetamine, in the 1960s, led to the monoamine theories of depression being postulated; first, with noradrenaline then 5-hydroxytryptamine being considered the more important amine. These monoamine theories of depression predominated both industrial and academic research for four decades. Recently, in attempts to design new drugs with faster onsets of action and more universal therapeutic action, downstream alterations common to current antidepressants are being examined as potential antidepressants. Additionally, the use of animal models has identified a number of novel targets some of which have been subjected to clinical trials in humans. However, monoamine antidepressants remain the best current medications and it may be some time before they are dislodged as the market leaders.

Novel Ligands for the Investigation of Imidazoline Receptors and Their Binding Proteins

New ligands for imidazoline receptors are described so that these receptors can be more fully explored and understood. BU224, (2-(4,5-dihydroimidaz-2-yl)-quinoline, shows high affinity and is selective for the imidazoline-2 (I(2)) class of receptors. BU224 was tested in the rat Porsolt forced swim paradigm where it was found to decrease time spent immobile and increase the time spent swimming, consistent with an antidepressant profile. BU224 was tritiated and, in radioligand binding studies, was found to label a single population of saturable sites with high affinity. In vitro brain autoradiography with [(3)H]BU224 also showed a pattern of distribution similar to the known labeling of I(2) receptors. A new series of four 2BFI (2-(benzofuranyl)-2-imidazoline) derivatives were investigated as potential ligands for imaging brain I(2) receptors using positron emission tomography (PET). At least two, BU20012 and BU20013, retained high affinity and moderate selectivity and penetrated the brain when administered peripherally in the mouse. 2BFI has undergone the Mannich reaction to immobilized diaminodipropyl amine to fabricate an affinity column, which was used to isolate a protein from rabbit brain; this protein was sequenced and identified as the enzyme creatine kinase.

In Vivo Estimation of Imidazoline2 Binding Site Turnover

Turnover of imidazoline(2) (I(2)) binding sites in the mouse and rat brain has been measured following an acute intravenous dose of BU99006. This ligand selectively and irreversibly knocks out I(2) sites, as defined by [(3)H]2BFI binding. Recovery was measured using radioligand binding and autoradiography to determine global and regional changes in I(2) density. The density of I(2) sites in brain recovered from BU99006 treatment with a half-life of 2.1 hours in mice and 4.3 hours in rats. Monoamine oxidase (MAO) activity and MAO binding density were unaltered in the brains of BU99006-treated animals. These data suggest that the I(2) site that reacts with BU99006 recovers rapidly and is independent of MAO.

Relationship Between Imidazoline2 Sites and Monoamine Oxidase

I(2) site-selective compounds are known to interact with and inhibit monoamine oxidase (MAO), but it remains unclear as to whether this interaction occurs through an allosteric or competitive interaction. This study used the new selective, irreversible I(2) ligand BU99006, to clarify the relationship between MAO and the I(2) binding sites (I(2)-BS). Results demonstrate that irreversible binding of BU99006 to rat brain membranes does not inhibit the enzyme or interfere with its interaction with other imidazoline enzyme inhibitors. This finding suggests that the I(2) sites that react with BU99006 are not those implicated in MAO inhibition and points to the existence of at least two distinct I(2) binding proteins.

Investigation of the Affinities of Two New b-Carbolines for Rat Brain Imidazoline2 Receptors

The beta-carbolines are possible endogenous ligands and modulators of the imidazoline binding sites (I-BSs). Relatively little is known about this class of compound and its interaction with the I-BS. Presented here are the binding data for two aryl ring substituted dihydro-beta-carbolines at the imidazoline(2) binding site (I(2)-BS) and alpha(2)-adrenoceptor: BG-326 (5-bromo-4,9-dihydro-3H-b-carboline) and BG-350 (5-methoxy-4,9-dihydro-3H-b-carboline). Both compounds show good affinity and selectivity for the I(2)-BS.

Endogenous -Carbolines as Clonidine-Displacing Substances

Endogenous beta-carbolines, such as harmane, are known to occur in mammalian species including humans. Radioligand binding studies have revealed that certain beta-carbolines display high affinity for both I(1) and I(2) imidazoline-binding sites (IBS). Functional studies have shown that the beta-carboline harmane elicits many characteristics expected of an endogenous ligand IBS. This article discusses the evidence relating to beta-carbolines as endogenous ligands and presents a case for harmane and related compounds as endogenous ligands for IBS.

Identification of an I2 Binding Protein From Rabbit Brain

Imidazoline-2 binding proteins exist as a heterogeneous population. The aim of this study was to isolate and identify I(2) binding proteins from rabbit brain using an affinity column synthesized with a highly selective I(2) ligand, 2-(2-benzofuranyl)2-imidazoline (2BFI). The results revealed an approximately 45-kD protein to be brain creatine kinase (EC 2.7.3.2). [(3)H]-2BFI (5nM) was able to bind specifically to the purified enzyme. This study has identified brain creatine kinase as a novel I(2) binding protein.

Initial Evaluation of Novel Selective Ligands for Imidazoline2 Receptors in Rat Whole Brain

Indazim, the indazole analogue of 2BFI, and four methyl-substituted analogues were tested for their affinity at the imidazoline(2) binding site (I(2)-BS), and this affinity was compared with their affinity at the alpha(2)-adrenoceptor to determine their structure, affinity relationship, and selectivity at the I(2)-BS. These studies showed that these ligands were highly selective for the I(2)-BS compared with 2BFI and that substitution at the 4 and 7 positions increased affinity without affecting selectivity.

BU98008, a Highly Selective Imidazoline1-Receptor Ligand

BU98008 (1-(4, 5-dihydro-1H-imidazol-2-yl)isoquinoline) is a novel isoquinoline derivative. Radioligand binding studies revealed it had high affinity for the I(1) receptor in rat kidney membranes but low affinity for the I(2) binding site and alpha(2)-adrenoceptor in rat brain membranes. Further evaluation of BU98008 in vivo revealed no effect on blood pressure following peripheral administration. These preliminary data suggest BU98008 may be an antagonist at I(1) receptors. Further evaluation following central administration must be performed before a hypotensive action can be excluded.

Characterization of [3H]Harmane Binding to Rat Whole Brain Membranes

This study investigates the binding of [(3)H]harmane to rat whole brain homogenates. Saturation studies revealed [(3)H]harmane labels a single, saturable, high-capacity population with high affinity. All the test compounds displaced [(3)H]harmane completely and in an apparently monophasic manner. The displacement profile of the test ligands indicated labeling of MAO-A. Given the high level of MAO-A binding, it is unlikely that a low-capacity I(2) site would be distinguishable from the total [(3)H]harmane population.

2-(4,5-Dihydro-1H-imidazol-2-yl)indazole (indazim) derivatives as selective I2 imidazoline receptor ligands

A series of variously substituted 2-(4,5-dihydro-1H-imidazol-2-yl)indazoles 3a-j and 2-(4,5-dihydro-1H-imidazol-2-yl)-4,5,6,7-tetrahydroindazole 6 were prepared by the regiospecific heteroalkylation of corresponding indazoles 1a-k with 2-chloro-4,5-dihydroimidazole (2). Their affinity to imidazoline I(2) receptors and alpha(2)-adrenergic receptors was determined by radioligand binding assay carried out on P(2) membrane preparations obtained from rat whole brains. 4-Chloro-2-(4,5-dihydro-1H-imidazol-2-yl)indazole (3f, 4-Cl-indazim) showed a 3076-fold difference in affinity for the [(3)H]2BFI-labeled imidazoline I(2) receptors relative to the [(3)H]RX821001-labeled alpha(2)-adrenergic receptors. This highly selective compound should prove to be useful tool in further understanding the functions of the imidazoline I(2) receptors.

5-Isothiocyanato-2-benzofuranyl-2-imidazoline (BU99006) an irreversible imidazoline(2) binding site ligand: in vitro and in vivo characterisation in rat brain

5-Isothiocyanato-2-benzofuranyl-2-imidazoline (BU99006) is an irreversible ligand based on the highly selective I(2) binding site ligand 2BFI. In competition binding assays it has been shown to have high affinity and selectivity for the I(2) binding site and to irreversibly inhibit the binding of [(3)H]2BFI. In this present study we have sought to confirm and expand on these findings both in vitro and in vivo. In vitro pre-incubation of rat whole brain membranes with BU99006 (10 microM) was shown to reduce the specific binding of [(3)H]2BFI to 10% of the control values, an effect not seen using 2BFI or BU224. Pre-treatment of rat whole brain membranes by BU99006, or by the alpha(2)-adrenoceptor antagonists RX821002 or rauwolscine had no effect on the specific binding of [(3)H]RX821002. In vivo pre-treatment of rats with BU99006 (15 mg x kg(-1), i.v.) caused a substantial loss of [(3)H]2BFI specific binding in subsequent in vitro saturation analysis and autoradiography; this loss was shown to be dose dependent. These data indicate that BU99006 is selectively and irreversibly affecting I(2) binding sites both in vitro and in vivo and that it represents an invaluable tool in the further understanding of the I(2) binding site.

Imidazoline(2) (I(2)) binding site- and alpha(2)-adrenoceptor-mediated modulation of central noradrenergic and HPA axis function in control rats and chronically stressed rats with adjuvant-induced arthritis

The aim of this study was to investigate imidazoline(2) (I(2)) binding site- and alpha(2)-adrenoceptor-mediated control of central noradrenergic and HPA axis activity in control rats and chronically stressed rats with adjuvant-induced arthritis (AA). Basal levels of extracellular nonadrenaline (NA) in the region of the hypothalamic paraventricular nucleus (PVN) of AA rats were significantly greater than controls. Both the I(2) binding site selective ligand BU224 (10 mg kg(-1) i.p.) and the alpha(2)-adrenoceptor antagonist RX821002 (2.5 mg kg(-1) i.p.) significantly elevated extracellular levels of NA in the PVN region and plasma corticosterone (CORT) in a rapid and transient manner in both control and AA rats. The noradrenergic response of AA rats to BU224 was significantly enhanced compared with drug treated controls. There was a significant correlation between extracellular NA in the PVN region and plasma CORT following BU224 and RX821002. In conclusion, central noradrenergic and HPA axis activity in control and chronically stressed AA rats appear to be under the control of both I(2) binding sites and alpha(2)-adrenoceptors. Increased basal levels of extracellular NA in the PVN region of AA rats suggests increased noradrenergic activity in these animals which is modulated to a greater extent by I(2) binding sites than by alpha(2)-adrenoceptors.

beta-carboline binding to imidazoline receptors

A series of beta-carbolines were prepared and their affinities for imidazoline (I(1) and I(2)) sites evaluated. Selected compounds were also examined at alpha(2)-adrenoceptors. Some of the beta-carbolines were found to bind with high affinity to I(2)-sites and this affinity was dependent on both the planarity of the molecule and the presence of the aryl ring substituents. Good I(1)-affinity was observed with two of the compounds but none of the tested compounds bound to alpha(2)-adrenoceptors. The hallucinogenic properties of beta-carbolines have been linked to activity at 5-HT receptors, in particular 5-HT(2), however, it is apparent from this study that many of these compounds display substantially higher affinity for the imidazoline sites. This finding, and those showing modulation of some behavioural effects of morphine by I(2)-ligands, suggests that imidazoline sites may be interesting new targets in drug abuse research.

Social interactions, perceived support, and level of distress in HIV-positive women

Although powerful pharmacological therapies are helping women with HIV infection live longer, women continue to experience the stressors of chronic illness. This study used a person-environment systems framework to describe social interactions, perceived social support, and psychological distress in HIV-positive women. A convenience sample of 104 HIV-positive women living in the San Francisco Bay Area completed a questionnaire on social interactions, perceived social support, and distress. Women reported limited social interactions with family and friends and a low level of perceived social support. Social support and level of distress did not differ by ethnicity. Limited perceived social support was a significant predictor of distress in this sample of women. Supportive interactions from health care providers can be useful in mediating the relationship between the stressor of HIV disease and distress in HIV-positive women. Community-based nurses can enhance HIV-positive women's support network by providing positive and supportive interactions as they intervene with women in symptom management, case management, and other health care services.

Selective delta-opioid receptor ligands: potential PET ligands based on naltrindole

Two series of delta-selective ligands related to the prototypic delta-antagonist naltrindole have been prepared and evaluated in opioid binding assays with the aim of developing new PET ligands for the delta-opioid receptor. One compound (5d) had significantly higher selectivity than naltrindole, but with substantially reduced binding affinity. For those compounds retaining similar affinity to naltrindole, those having ethyl and fluoroethyl substituents afforded the highest levels of selectivity. However, none of the compounds combined the high level of affinity and selectivity ideally suited to the development of an imaging agent.

Behavioural and physiological effects induced by an infusion of antisense to alpha(2D)-adrenoceptors in the rat

1. The aim of this study was to investigate the behavioural and physiological effects of an i.c.v. infusion of antisense oligonucleotide to the alpha(2D)-adrenoceptor subtype. Behavioural and physiological parameters were monitored for 2 days before the infusion, throughout the 3-day infusion period and for 3 days following the end of the infusion. 2. The antisense infusion resulted in a significant increase in behavioural activity characterized by increased locomotion and grooming scores. Behavioural activity scores of rats treated with antisense to alpha(2D)-adrenoceptors were significantly higher than those of rats treated with vehicle (H(2)O) or the mismatch toxicity control on day 4 and day 5 and, significantly higher than vehicle controls on day 6. 3. Body weight gain was significantly reduced in the antisense-treated rats at the end of the study compared to the vehicle (34%) and mismatch groups (30%), although daily food and water intakes were not significantly different at any time point. 4. Pupil diameters of rats infused with antisense to alpha(2D)-adrenoceptors were significantly greater than those of animals treated either with vehicle or mismatch oligonucleotide on day 5 of the study. On day 6, the pupil diameters of these animals were still significantly greater than the mismatch group. 5. In conclusion, an i.c.v. infusion of antisense to the alpha(2D)-adrenoceptor induced behavioural activation in rats, increased pupil diameter and reduced total weight gain. These effects were specific to the antisense-treated group and were fully reversed post-infusion.

Probes for imidazoline binding sites: synthesis and evaluation of a selective, irreversible I2 ligand

An irreversible ligand (7) has been prepared based on the selective I2 ligand 2-BFI. Compound 7 displayed high affinity and selectivity for I2-sites and has been shown to irreversibly bind to these sites in rat brain. Compound 7 should, therefore, prove an invaluable tool for the further elucidation of I2-site function.

Isolation of RP-HPLC pure clonidine-displacing substance from NG108-15 cells

A crude extract of clonidine-displacing substance (CDS) has previously been extracted from the NG108-15 cell line. This study aimed to purify CDS extracted from this cell line further, by the technique of reverse phase-HPLC (RP-HPLC), and subsequently determine whether this refined CDS bears any similarity to CDS's extracted from other tissues. Crude CDS was extracted from NG108-cells and fractionated by RP-HPLC eluting with a linear gradient of methanol (5-65%; 1 ml min(-1) flow rate) over 50 min., and collected at 1 min. intervals. The pharmacological activities of the CDS fractions were determined by their abilities to displace bound [3H]clonidine to alpha(2)-adrenoceptors in rat brain membranes. RP-HPLC analysis of CDS revealed a pharmacologically active fraction distinct from agmatine, eluting at 24 min, corresponding to an absorbance peak observed at this time. Collectively, these results confirmed that CDS was present in the NG108-15 cell line. However, the RP-HPLC analysis showed the pharmacological activity to elute at a more hydrophobic gradient than previously observed with CDS's extracted from bovine tissues. These results support the notion of the existence of several CDS's.

In vitro and in vivo approaches to the characterization of the alpha2-adrenoceptor

1. In order to more fully understand the role of the alpha2-adrenoceptor in brain function, a combination of in vitro and in vivo techniques were utilized including radioligand binding, autoradiography, brain microdialysis and antisense oligonucleotides. 2. Binding studies showed the tritiated form of the selective alpha2-adrenoceptor antagonist, RX821002 (methoxy-idazoxan) labelled an apparent single population of sites in rat brain membranes with high affinity (1 nM), for which prazosin had low affinity (1107 nM). Similar studies in rabbit brain membranes found that prazosin and oxymetazoline were able to displace [3H]-RX821002 in a biphasic manner indicating the presence of subtypes of alpha2-adrenoceptors. 3. Receptor autoradiography revealed a distribution of [3H]-RX821002 binding in rat brain consistent with the labelling of all alpha2-adrenoceptor subtypes, namely alpha(2A/D-), alpha2B and alpha2C. 4. In rat, in vivo brain dialysis experiments demonstrated peripherally administered RX821002 elevated basal noradrenaline in frontal cortex and also, although to a lesser extent, in ventral hippocampus. RX821002 was also able to elevate extracellular dopamine in the striatum. 5. A 7-day i.c.v. infusion of an antisense oligonucleotide targeting the alpha(2A/D)-adrenoceptor, resulted in a significant reduction in the autoradiographic density of [3H]-RX821002 binding in specific brain areas, notably the lateral septal nuclei and anterior hypothalamic area. 6. Several years of research by our group has extended our knowledge of the pharmacology and function of the alpha2-adrenoceptor and has provided evidence of the roles of this receptor in the control of monoamine turnover. The successful use of antisense technology to knockdown expression of the alpha(2A/D) subtype provides future opportunities to explore the physiology of this receptor subtype.

Autoradiographical and behavioural effects of a chronic infusion of antisense to the alpha2D-adrenoceptor in the rat

1. The aims of this study were, firstly to use receptor autoradiography to investigate the effect of antisense oligonucleotides to the alpha2D-adrenoceptor on receptor binding and, secondly to measure behavioural and physiological parameters to determine whether the chronic antisense infusion had any effect on alpha2-adrenoceptor function in vivo. 2. A 3 day infusion of antisense to the alpha2D-adrenoceptor significantly reduced specific [3H]-RX821002 binding in the septum (20 - 30%) and anterior hypothalamic area (20 - 30%). beta-Adrenoceptor expression was unaffected in those brain areas examined, indicating the antisense knockdown was specific to the alpha2-adrenoceptors. 3. On the second day of the infusion, the hypothermic response to UK 14,304 was significantly attenuated in the antisense-treated group compared with both vehicle and mismatch controls. The effect was fully reversible and a similar decrease in body temperature was observed in all the treatment groups 4 days after the end of infusion. 4. During the second day of the infusion, the effects of UK 14,304 on behaviour were reduced in the antisense-treated rats, but were not significantly lower than those of the vehicle and mismatch, UK 14, 304 controls. These trends were not observed 4 days after the end of the infusion. 5. In conclusion, antisense has been shown to selectively knockdown alpha2-adrenoceptor expression in specific brain areas. The consequence of this knockdown is a significant attenuation of UK 14,304-induced hypothermia and a reduction in its sedative actions. These changes were fully reversed 4 days after the end of the infusion.

Extraction of active clonidine-displacing substance from bovine lung and comparison with clonidine-displacing substance extracted from other tissues

Crude methanolic clonidine-displacing substance (CDS) extracted from bovine lung competed for radioligand binding from alpha2-adrenoceptors and I2-sites present in rat brain membranes, and from I1-sites present in rat brain and kidney membranes. There was no difference in the competition of [3H]clonidine binding to alpha2-adrenoceptors present in either rat or rabbit brain membranes by the crude CDS extract and therefore either tissue could be used to estimate the number of units of CDS present in extracts. Further purification by reverse phase high performance liquid chromatography (RP-HPLC), with UV detection, of extracts obtained from bovine lung, brain and rat brain exhibited similar three-peak profiles, previously reported. Corresponding fractions competed for radioligand binding to alpha2-adrenoceptors present in rat brain membranes, eluting between 19 and 23 min, which corresponded with the middle peak of the three-peaks. Therefore, we propose the CDS-like material eluting from all these tissues to be similar. Interestingly, CDS extracted from bovine adrenal glands under the same conditions showed a similar three-peak profile, but did not repeat the displacement of binding just at 19-23 min, but at every time point after 4 min. This suggests this tissue could represent a source of CDS in this species.

Novel selective compounds for the investigation of imidazoline receptors

Over several years our group has sought to synthesize and identify selective ligands for imidazoline (I) receptors, in particular the I2 binding site. As a consequence, [3H]2-(2-benzofuranyl)-2-imidazoline (2BFI) has proved extremely useful for binding and autoradiographic studies. More recently we have synthesized a BU series of compounds and examined these for their affinities for both I1 and I2 binding sites. BU224 (2-(4,5-dihydroimidaz-2-yl)-quinoline) shows high affinity for I2 receptors with a Ki of 2.1 nM. BU226 (2-(4,5-dihydroimidaz-2-yl)-isoquinoline) demonstrated slightly higher affinity (Ki 1.4 nM) for I2 receptors, but overall BU224 displayed greater selectivity for I2 over I1 receptors (832-fold) than BU226 (380-fold). Both compounds showed low (microM) affinity for alpha 2-adrenoceptors. Given BU224's ability to cross the blood brain barrier, we predict that its in vivo effects are likely to be mediated via I2 receptors. Brain dialysis revealed BU224 to dose dependently (0-20 mg/kg i.p.) elevate basal noradrenaline in rat frontal cortex and basal dopamine in striatum. In a rat model of opiate withdrawal, behavioral studies showed that BU224 (10 mg/kg, s.c.) was able to reduce acute weight loss and diarrhea, but not the number of wet dog shakes associated with the withdrawal syndrome.

Potentiation of barbiturate-induced alterations in presynaptic noradrenergic function in rat frontal cortex by imidazol(in)e alpha2-adrenoceptor agonists

1. In order to resolve the extent to which presynaptic noradrenergic mechanisms contribute to the anaesthetic-sparing effects of alpha2-adrenoceptor agonists in vivo microdialysis was used to investigate the combined effects of sodium pentobarbitone and imidazol(in)e alpha2-adrenoceptor agonists on extracellular levels of noradrenaline (NA) in the rat frontal cortex. 2. Dialysate levels of NA were markedly reduced by the addition of TTX (2 microM) or by the removal of calcium in the perfusate. These data imply that dialysate NA levels are ultimately dependent on exocytotic release mechanisms from afferent coeruleo-cortical neurones. 3. Systemic administration of sodium pentobarbitone (85 mg kg(-1), i.p.) induced general anaesthesia and reduced NA levels by 92% after 30 min. The restoration of basal levels 90 min later was closely associated with a return of the corneal blink reflex. 4. Basal NA levels in conscious animals were not affected by an intravenous infusion of equally radioactive solutions of either imidazoline (clonidine) or imidazole (mivazerol) alpha2-adrenoceptor agonists. The dose rate employed for each compound was 2 microg kg(-1) h(-1) over 2 h. 5. The co-administration of intravenous clonidine or mivazerol, each at 2 microg kg(-1) h(-1) for 2 h, with sodium pentobarbitone (85 mg kg(-1), i.p.), produced a marked and prolonged reduction in NA efflux. After 2 h, NA levels remained suppressed by 95% (clonidine) and 80% (mivazerol) and animals remained deeply anaesthetized. 6. The accumulation of tritium in brain tissue was 42-73% lower across all brain regions examined after [3H]-mivazerol administration than after [3H]-clonidine administration. Sodium pentobarbitone did not alter the accumulation of tritium in brain tissue after the administration of either alpha2-adrenoceptor agonist. 7. These data demonstrate that alpha2-adrenoceptor agonists potentiate the inhibitory effects of sodium pentobarbitone on extracellular levels of NA in the frontal cortex. Further studies will be necessary to establish a causal role of noradrenergic mechanisms in the potentiation of anaesthesia by selective alpha2-adrenoceptor agonists.

'Seeing through a glass darkly': casting light on imidazoline 'I' sites

Although imidazoline sites have been the subject of research for several years, there is still controversy about their structure, diversity and physiology. The I1 site is thought to exist principally as a binding site and is widely purported to play a role in controlling systemic blood pressure, although this is still unclear. The majority of I2 sites are widely accepted as being allosteric sites on monoamine oxidase; however, even with selective ligands, their exact function remains to be determined. A putative I3 site modulates insulin secretion and could represent the first functional site to be pharmacologically defined with selective agonists and antagonists. The structure and relevance of the proposed endogenous ligand 'clonidine-displacing substance' remains elusive. A potential candidate for this substance is agmatine; however, although it is capable of displacing bound clonidine from imidazoline sites, it lacks the functionality ascribed to the clonidine-displacing substance. In this review, Richard M. Eglen and colleagues assess our knowledge of imidazoline sites in the light of recent data.

Characterisation and localisation of [3H]2-(2-benzofuranyl)-2-imidazoline binding in rat brain: a selective ligand for imidazoline I2 receptors

In rat whole brain homogenates, saturation binding analysis revealed that both [3H]2-BFI (2-(2-benzofuranyl)-2-imidazoline) and [3H]idazoxan (in the presence of 5 microM rauwolscine) bound with high affinity to an apparent single population of sites. However, the Kd for [3H]2-BFI (1.74+/-0.14 nM) was significantly (P < 0.01) less than that for [3H]idazoxan (10.4+/-2.68 nM). In competition studies idazoxan, 2-BFI, BU224 (2-(4,5-dihydroimidaz-2-yl)-quinoline), amiloride and guanabenz displayed high affinity (Ki values = 7.32, 1.71, 2.08, 21.80 and 14.90 nM, respectively) for 70-80% of sites, and low microM affinity for the remaining 20-30% of sites labelled by [3H]2-BFI. In contrast, several alpha2-adrenoceptor, imidazoline I1 receptor and histamine receptor ligands exhibited only micromolar affinity for the [3H]2-BFI labelled site. Quantitative receptor autoradiography revealed high binding by [3H]2-BFI to discrete brain nuclei, notably the area postrema, interpeduncular nucleus, arcuate nucleus, mammillary peduncle, ependyma and pineal gland. These data indicate that [3H]2-BFI recognises imidazoline I2 receptors in rat brain with higher affinity and selectivity than [3H]idazoxan and thus represents a superior radioligand to [3H]idazoxan for the study of imidazoline I2 receptors.

Antisense oligonucleotides in psychopharmacology and behaviour: promises and pitfalls

Antisense oligonucleotides are used to study the expression and function of a diverse range of proteins. Areas for which antisense has been used for pharmacological investigation include receptors, neuropeptides and immediate early genes, particularly when specific ligands or markers are not yet available. Antisense oligonucleotides target a specific mRNA and block the expression of the protein by sequence specific hybridization. This technique has not only been shown to be a valuable pharmacological tool but also to have potential therapeutic applications. In this review we discuss the technology behind the technique including developments in methodology employed in antisense experiments. Although antisense provides a novel and highly specific tool, the reliability of the technique and many of the problems associated with antisense experiments are discussed. The main focus of this article is the use of antisense in psychopharmacology to investigate behavioural changes following antisense-mediated inhibition of the expression of specific brain proteins and receptors.

Characteristics of GABAB receptor binding sites on rat whole brain synaptic membranes. 1983

Saturable binding of (±)-[³H]-baclofen and [³H]-γ-aminobutyric acid ([³H]-GABA) to rat brain crude synaptic membranes has been examined by means of a centrifugation assay.

The binding of [³H]-baclofen could be detected in fresh or previously frozen tissue and was dependent on the presence of physiological concentrations of Ca²⁺ or Mg²⁺ although a lower affinity Na⁺-dependent component could also be observed. Both components probably reflect binding to receptor recognition sites.

The saturable portion of bound [³H]-baclofen formed 20.3 ± 6.9% of total bound ligand. This could be displaced by GABA (IC₅₀ = 0.04 μm), (–)-baclofen (0.04 μm) and to a much lesser extent by (+)-baclofen (33 μm). Isoguvacine, piperidine-4-sulphonic acid and bicuculline methobromide were inactive (up to 100 μm) and muscimol was only weakly active (IC₅₀ = 12.3 μm).

Saturable binding of [³H]-GABA increased on adding CaCl₂ or MgSO₄ (up to 2.5 Mm and 5.0 Mm respectively) to the Tris-HCl incubation solution. This binding (GABA_B site binding) was additional to the bicuculline-sensitive binding of GABA (GABA_A site binding) and could be completely displaced by (–)-baclofen (IC₅₀ = 0.13 μm).

Increasing the Ca²⁺ concentration (0 to 2.5 Mm) increased the binding capacity of the membranes without changing their affinity for the ligand.

The binding of [³H]-GABA to GABA_B sites could be demonstrated in fresh as well as previously frozen membranes with a doubling of the affinity being produced by freezing. Further incubation with the non-ionic detergent Triton-X-100 (0.05% v/v) reduced the binding capacity by 50%.

The pharmacological profile of displacers of [³H]-GABA from GABA_B sites correlated well with that for [³H]-baclofen displacement. A correlation with data previously obtained in isolated preparations of rat atria and mouse vas deferens was also apparent.

It is concluded that [³H]-baclofen or [³H]-GABA are both ligands for the same bicuculline-insensitive, divalent cation-dependent binding sites in the rat brain.

Noradrenergic mechanisms in the prefrontal cortex

There is growing evidence that noradrenergic inputs to the prefrontal cortex (PFC) play an important role in regulating its function. This paper reviews the pharmacological control of noradrenaline (NA) release in this region, with particular reference to our studies using brain microdialysis, and also describes how NA levels are modulated by antidepressant and antipsychotic drugs. The suggestion that atypical antipsychotics such as clozapine and risperidone may produce clinical benefits by their ability to increase NA release is discussed. Finally, a new class of drugs, which show selectivity for imidazoline receptors is described. These compounds are shown to similarly increase extracellular NA in the PFC. Their potential utility as clinical treatments is discussed.