The influence of volume exclusion by chromatin on the time required to find specific DNA binding sites by diffusion.

Within the nuclei of eukaryotic cells, the density of chromatin is nonuniform. We study the influence of this nonuniform density, which we derive from microscopic images [Schermelleh L, et al. (2008) Science 320:1332-1336], on the diffusion of proteins within the nucleus, under the hypothesis that chromatin density is proportional to an effective potential that tends to exclude the diffusing protein from regions of high chromatin density. The constant of proportionality, which we call the volume exclusivity of chromatin, is a model parameter that we can tune to study the influence of such volume exclusivity on the random time required for a diffusing particle to find its target. We consider randomly chosen binding sites located in regions of low (20th-30th percentile) chromatin density, and we compute the median time to find such a binding site by a protein that enters the nucleus at a randomly chosen nuclear pore. As the volume exclusivity of chromatin increases from zero, we find that the median time needed to reach the target binding site at first decreases to a minimum, and then increases again as the volume exclusivity of chromatin increases further. Random permutation of the voxel values of chromatin density abolishes the minimum, thus demonstrating that the speedup seen with increasing volume exclusivity at low to moderate volume exclusivity is dependent upon the spatial structure of chromatin within the nucleus.

Acupuncture increases parasympathetic tone, modulating HRV - Systematic review and meta-analysis.

INTRODUCTION: An increasing number of studies have demonstrated that acupuncture can influence Autonomic Nervous System functions. Heart Rate variability (HRV) is one widely used marker of autonomic activity. The main objective of this systematic review is to critically assess the evidence from randomized clinical trials (RCTs) regarding the effect of acupuncture on HRV as compared to placebo methods. METHOD: EMBASE, Pubmed, The Cochrane Library, Web of Science, Scopus electronic databases were searched until 9 September 2020 for RCTs in which human subjects were treated with needle acupuncture using acupoints of the body without electric stimulation. RESULTS: The searches identified 1698 potentially relevant articles, 9 RCTs were included. The statistical analysis of the available data showed that the changes between pre and post treatment HF (high frequency) and LF/HF (high frequency/low frequency) values in Verum group were significant, while there were no significant changes in these parameters in Sham groups. CONCLUSION: the results of this meta-analysis suggest that real acupuncture has superior effect over placebo acupuncture in increasing parasympathetic tone and in this way may improve physical well-being. Due to the quality of primary studies and degree of heterogeneity the results should be interpreted cautiously.

Clomifene citrate and intrauterine insemination as first-line treatments for unexplained infertility: are they cost-effective?

BACKGROUND: First-line treatments for unexplained infertility traditionally include clomifene citrate (CC) or unstimulated intrauterine insemination (IUI). A recently published randomized controlled trial considered the effectiveness of CC and IUI in patients with unexplained infertility and found that neither treatment offered a superior live birth rate when compared with expectant management (EM). This paper reports the economic evaluation conducted alongside this trial in order to assess whether health care providers are gaining value for money in this clinical area. METHODS: Five hundred and eighty women across five Scottish hospitals were randomized to either EM, CC or IUI for 6 months. The primary outcome measure was live births. Resource-use data were collected during the trial and costs were calculated from a UK National Health Service (NHS) perspective. Incremental cost-effectiveness ratios were calculated, expressed as cost per live birth, in order to compare the cost-effectiveness of CC and IUI with that of EM to treat unexplained infertility. RESULTS: Live birth rates in the three randomized groups were: EM = 32/193 (17%), CC = 26/194 (13%) and IUI = 43/193 (22%). The mean (standard deviation) costs per treatment cycle were £0 for EM, £83 (£17) for CC and £98 (£31) for IUI. The mean treatment costs per patient for EM, CC and IUI were £12 (£117), £350 (£220) and £331 (£222), respectively. The cost per live birth for EM, CC and IUI was £72 (95% confidence interval £0-£206), £2611 (£1870-£4166) and £1487 (£1116-£2155), respectively. The incremental cost-effectiveness ratio for IUI versus EM was £5604 (-£12204 to £2227), with CC dominated by IUI. CONCLUSIONS: Despite being more expensive, existing treatments such as empirical CC and unstimulated IUI do not offer superior live birth rates compared with EM of unexplained infertility. They are unlikely to be a cost-effective use of limited NHS resources. The study's main limitation is that it did not consider the psychological effects on couples. ISRCT Number: 71762042.

Effects of fish and plankton and lake temperature and mixing depth.

A comparative study of small temperate lakes (<20 square kilometers) indicates that the mixing depth or epilimnion is directly related to light penetration measured as Secchi depth. Clearer lakes have deeper mixing depths. This relation is the result of greater penetration of incident solar radiation in lakes and enclosures with high water clarity. Data show that light penetration is largely a function of size distribution and biomass of algae as indicated by a relation between the index of plankton size distribution (slope) and Secchi depth. Larger or steeper slopes (indicative of communities dominated by small plankton) are associated with shallower Secchi depth. In lakes with high abundances of planktivorous fish, water clarity or light penetration is reduced because large zooplankton, which feed on small algae, are reduced by fish predation. The net effect is a shallower mixing depth, lower metalimnetic temperature and lower heat content in the water column. Consequently, the biomass and size distribution of plankton can change the thermal structure and heat content of small lakes by modifying light penetration.

Endothelin-1 activates ETA receptors to cause reflex scratching in BALB/c mice.

BACKGROUND AND PURPOSE: Endothelin-1 (ET-1) is present in murine and human skin and causes itch (pruritus) when injected in humans. This behavioural study examined the scratch reflex evoked by ET-1 in mice. EXPERIMENTAL APPROACH: An automated detector was used to determine whether ET-1 causes reflex scratching, the behavioural correlate of itching, in BALB/c mice. Selective agonists and antagonists were used to probe the ET receptor(s) involved. KEY RESULTS: ET-1 evoked dose-related reflex scratching lasting up to 20 min following intradermal injection (0.1-100 ng; 0.04-40 pmol). The ED(50) for ET-1 induced scratching was 2.1 ng and desensitization occurred with cumulative dosing. High doses of the ET(B) receptor agonist IRL1620 (10 microg; 5.5 nmol), also caused scratching (ED(50) 1.3 microg, 0.7 nmol). The ET(A) receptor antagonist BQ123 significantly reduced scratching evoked by ET-1 and IRL 1620, suggesting that both agonists caused scratching via an ET(A) receptor-dependent mechanism. The ET(B) receptor antagonist BQ788 significantly reduced scratching evoked by IRL1620 but had no effect on scratching evoked by ET-1. This indicated that activation of ET(B) receptors by high doses of ET(B) agonist, but not ET-1, can trigger scratching. CONCLUSION AND IMPLICATIONS: ET-1 is a potent endogenous activator of reflex scratching (itch). Mechanisms for ET-induced scratching are considered, including direct action of ET-1 on pruriceptive nerve endings and indirect actions via release of endogenous mediators such as histamine from mast cells. ET-1 and ET(A) receptors, possibly also ET(B) receptors, are potential targets for developing specific anti-pruritic drugs to treat pruritic skin disorders such as atopic dermatitis.

A repetitive movement detector used for automatic monitoring and quantification of scratching in mice.

We have designed an economical non-invasive movement detector for small animal studies and used it for monitoring and quantifying itch in mice. The system is based on a sensitive force transducer positioned below a recording platform holding a lightweight polystyrene recording box in which an animal is placed. A programmed micro-controller is used to discriminate between non-specific movement, grooming behaviour, and scratching movements made by the animal's hind limb. Following sub-dermal injection of histamine receptor agonists into the neck of a mouse, dose-related scratching occurred which was detected and quantified. There was 91% correlation between bouts of scratching as counted manually from playback of the video recording and recorded by the detector. The detector was also able rapidly to count the individual scratch movements of the hind limb that comprise a bout, with 95% accuracy in comparison with manual counting during slow motion playback of video tape, something that is impossible for an unaided observer to achieve because individual scratch movements are too fast to discriminate by eye. Separate detectors were used for the efficient non-invasive study of four animals simultaneously, and this number could easily be increased by adding more platforms. The system could also be modified to record the animal's position within the box, which would be of value in studies involving exploratory behaviour. In summary, the non-invasive multichannel repetitive movement detector will be very useful for accurate measurement of scratching during pruritus studies in small animals, with considerable savings in staff time and effort. It should therefore be a valuable tool for helping to investigate pruritus and in the evaluation of anti-pruritic drugs.

Global priority setting for Cochrane systematic reviews of health promotion and public health research.

BACKGROUND: Systematic reviews of health promotion and public health interventions are increasingly being conducted to assist public policy decision making. Many intra-country initiatives have been established to conduct systematic reviews in their relevant public health areas. The Cochrane Collaboration, an international organisation established to conduct and publish systematic reviews of healthcare interventions, is committed to high quality reviews that are regularly updated, published electronically, and meeting the needs of the consumers. AIMS: To identify global priorities for Cochrane systematic reviews of public health topics. METHODS: Systematic reviews of public health interventions were identified and mapped against global health risks. Global health organisations were engaged and nominated policy-urgent titles, evidence based selection criteria were applied to set priorities. RESULTS: 26 priority systematic review titles were identified, addressing interventions such as community building activities, pre-natal and early infancy psychosocial outcomes, and improving the nutrition status of refugee and displaced populations. DISCUSSION: The 26 priority titles provide an opportunity for potential reviewers and indeed, the Cochrane Collaboration as a whole, to address the previously unmet needs of global health policy and research agencies.

NICE recommendations for psychotherapy in depression: Of limited clinical utility.

In 2009/10 NICE partially updated its guidelines on the treatment and management of depression in adults. Due to methodological shortcomings the recommendations for psychotherapy must be treated with caution. Despite recognising the heterogeneous and comorbid nature of depression, and the limitations of depression as a unitary diagnostic category, NICE treats depression as if it were a unitary entity differentiated only by severity. The guidance ignores important aetiological factors such as trauma, loss and maltreatment, personality and interpersonal difficulties. It excludes the largest naturalistic studies on clinical populations treated in the National Health Service on the grounds that they are observational studies conducted in heterogeneous groups with mixed neurotic disorders. It unquestioningly accepts that the "brand" of psychotherapy has construct validity, and ignores psychotherapy process research indicating significant commonalities, and overlap, between treatment modalities and evidence that individual practitioner effects are larger than the differences between treatment modalities. It fails to consider patient differences and preferences, which are known to influence uptake, completion and response. It takes an exclusively short-term perspective on a chronic relapsing disorder. It does not consider the evidence for longer-term treatments. It is of special concern that NICE misrepresents the findings of its own systematic review by implying that CBT and IPT are superior treatments. NICE's systematic review actually found no evidence of superiority between CBT, IPT, psychodynamic psychotherapy, or counselling. Based on the exclusion of much clinically relevant research demonstrating the effectiveness of psychodynamic psychotherapy and counselling many commentators have alleged a bias towards CBT in the guidance. With regard to service delivery NICE proposes the replacement of psychiatric assessment and individualised treatment plans, with an unproven stepped-care model. These clinical and theoretical limitations, perceived bias in the selection of studies, neglect of patient differences, preferences and values, misrepresentation of results of the systematic review, and the proposal for an unproven service delivery model together seriously undermine the validity of the guidance. The guidance, lacking validity is of questionable use, it undermines patient autonomy, professional expertise and, ultimately, patient welfare.

Changing patterns in reported sexual practices in the population: multiple partners and condom use.

OBJECTIVE: To determine whether the pattern of change with regard to condom use and multiple sexual partners is influenced by gender or educational level. DESIGN: Findings from data collected from 1987 to 1990 about changes in condom use and multiple-partner activities are presented, based on telephone interviews with 9416 participants aged 18 to 44 years resident in central Scotland, UK. METHODS: Change in patterns over time were modelled in a multivariate logistic regression using a linear interactive modelling program. RESULTS: Several models showing changes in the proportion of multiple-partner respondents and condom users yielded a complicated pattern of behavioural change in educational status and gender. CONCLUSIONS: There is a large difference in reported condom use and multiple sexual partners by gender, but the difference is decreasing over time. Better educated respondents increased their use of condoms while less educated respondents showed a decrease in the proportion of multiple partners.

Prostanoid-induced potentiation of the excitatory and sensitizing effects of bradykinin on articular mechanonociceptors in the rat ankle joint.

Responses of articular mechanonociceptors to intra-arterial injections of either bradykinin alone or in combination with prostaglandin E2, prostaglandin I2 or the selective I-type prostaglandin receptor agonist cicaprost were investigated electrophysiologically in anaesthetized rats. Bradykinin excited 76% of the mechanonociceptors studied and increased their responsiveness to repeated mechanical stimuli in 70% of units. Tachyphylaxis of these responses was evident in all cases. Injections of minimally effective doses of prostaglandin I2 or cicaprost excited the mechanonociceptors and increased their responsiveness to mechanical stimuli. Injections of prostaglandin E2 evoked only small increases in spontaneous discharge. Potentiation of bradykinin-evoked excitation was seen for combined injections of bradykinin with minimally effective or subthreshold doses of cicaprost in 86% of units, prostaglandin I2 in 40% of units and prostaglandin E2 in 56% of units. Combined injections of bradykinin and minimally effective or subthreshold doses of prostanoid agonist caused an increase in the responsiveness of mechanonociceptors to mechanical stimuli greater than that caused by either drug alone in 80% of units for cicaprost, 80% for prostaglandin I2 and 100% for prostaglandin E2. The relative potencies of prostaglandin I2, cicaprost and prostaglandin E2, suggest that prostanoid-induced excitation and sensitization of articular mechanonociceptors is mediated primarily by receptors for the naturally occurring prostanoid prostaglandin I2 (I-type P-receptors). Prostaglandin E2 may be important in potentiation of the sensitizing effects of bradykinin on mechanonociceptor responsiveness.

The effects of some prostaglandins on respiration in anaesthetized cats.

1 Some prostaglandins have been found to be capable of affecting respiration in anaesthetized cats.2 Prostaglandins E(1), E(2), F(2alpha), A(1) and A(2) all elicited increases in respiratory frequency when administered to cats anaesthetized with either pentobarbitone or alpha-chloralose. This effect was abolished by bilateral vagotomy.3 Prostaglandins of the E and A series, but not prostaglandin F(2alpha), elicited increases in tidal volume which were accompanied by falls in systemic blood pressure in cats anaesthetized with pentobarbitone. The changes in blood pressure were also obtained in cats anaesthetized with alpha-chloralose, but not the tidal volume changes.4 It is unlikely that the prostaglandins influenced respiration by direct actions on arterial chemoreceptors or baroreceptors.5 Mechanisms by which the prostaglandins may be acting to affect respiration are discussed.

Effects of acetylcholine and sodium cyanide on cat carotid baroreceptors.

1 The effects of intracarotid (i.a.) injections of acetylcholine (ACh) and sodium cyanide (NaCN) on baroreceptor activity recorded from the sinus nerve have been investigated in cats anaesthetized with pentobarbitone.2 Two types of baroreceptor unit were recorded. The predominant type discharged at least 3 to 4 spikes per pulse wave at normal BP; they are referred to as ;polyspike' units and may have been associated with A fibres. The other type discharged a maximum of 1 to 3 spikes per pulse wave, even at high BP; they are referred to as ;few-spike' units and may have been from C fibres.3 NaCN had no direct effect on either type of baroreceptor unit, even when injected in high doses (2.04 to 5.1 mumol i.a.) which cause maximal chemoreceptor stimulation, and it is concluded that as far as the cat's carotid baroreceptors and chemoreceptors are concerned, NaCN is a specific chemoreceptor stimulant.4 ACh had no direct effect on polyspike baroreceptor units unless very high doses (1.83 mumol i.a.) were injected, when there was occasionally a transient slight increase in discharge. This effect appeared to be secondary to muscle contraction caused by ACh since it was not seen when an adequate neuromuscular-blocking dose of gallamine had been administered.5 ACh stimulated the few-spike type of baroreceptor unit, an effect which was dose-related and lasted for up to 3 s; the threshold dose for baroreceptor stimulation was higher than that needed to excite chemoreceptor units. The increased discharge also occurred during experiments in which gallamine had been administered. Only five of these units were recorded during the investigation, despite an intensive search for them.6 There was a delayed increase in baroreceptor sensitivity following the administration of ACh in doses (37 to 366 nmol i.a.) which had no immediate direct effect on polyspike baroreceptor discharge. The effect was evidently not secondary to changes in sympathetic nerve activity to the sinus region since it was observed during an experiment in which the ganglioglomerular nerves had been cut. Whether the increased sensitivity resulted from direct or indirect actions of ACh remains to be determined.7 It is concluded that low doses of ACh or other drugs with nicotinic properties are unlikely to evoke baroreceptor reflexes on intracarotid injection, although they may cause delayed changes in baroreceptor sensitivity. Higher doses of ACh do not directly affect baroreceptor polyspike (A fibre) units, but transient baroreflex changes might result from stimulation of baroreceptor few-spike (C fibre) units. It is most unlikely that NaCN has any direct effect on baroreceptor reflex activity when injected into the carotid artery in doses used to elicit chemoreceptor reflexes.

Inhibitory actions of methionine-enkephalin and morphine on the cat carotid chemoreceptors.

1 The effects of intracarotid injections of methionine-enkephalin (Met-enkephalin) and morphine on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve have been studied in cats anaesthetized with pentobarbitone. 2 Met-enkephalin caused a rapid, powerful, inhibition of spontaneous chemoreceptor discharge, the intensity and duration of which was dose-dependent. 3 Morphine was a less potent inhibitor of spontaneous chemoreceptor discharge, and the inhibition it evoked was rather variable and tended to be biphasic. Low doses of morphine caused a slight increase in discharge. 4 Naloxone (0.2 mg i.c.) slightly increased spontaneous discharge, greatly reduced the chemo-inhibition caused by morphine, and reduced the inhibitory effect of Met-enkephalin. A higher dose of naloxone (0.8 mg) caused a substantial reduction of the Met-enkephalin effect. 5 Chemo-excitation evoked by intracarotid injections of acetylcholine, CO2-saturated Locke solution, and sodium cyanide were only slightly and somewhat variably reduced following injections of Met-enkephalin, whereas the inhibitory effect of dopamine was potentiated. Following morphine administration, response to acetylcholine and sodium cyanide were reduced slightly, whereas those to CO2 and dopamine were potentiated. 6 Responses to acetylcholine and CO2 were slightly potentiated during infusion of Met-enkephalin (50 micrograms/min, i.c.) and the response to sodium cyanide was slightly reduced. 7 It is concluded that naloxone-sensitive opiate receptors are present in the cat carotid body; when activated they cause inhibition of spontaneous chemoreceptor discharge. The physiological role of these receptors and the identity of any endogenous ligand remains to be established.

Characterization of opioid receptors in the cat carotid body involved in chemosensory depression in vivo.

The effects of selective opioid receptor agonists and antagonists on neural discharge recorded from carotid body arterial chemoreceptors in vivo were studied in anaesthetized cats. Mean ID50 values were determined for each agonist and used to assess chemodepressant potency on intracarotid (i.c.) injection in animals artificially ventilated with air. [Met]enkephalin, [Leu]enkephalin, [D-Ala2, D-Leu5]enkephalin and [D-Pen2, D-Pen5]enkephalin were more potent chemodepressants than [D-Ala2, Me-Phe4, Gly-ol5]enkephalin, dynorphin (1-8) or ethylketocyclazocine; morphiceptin (mu-agonist) was inactive. The rank order of potency was compatible with the involvement of delta-opioid receptors in opioid-induced depression of chemosensory discharge. ICI 154129, a delta-opioid receptor antagonist, was used in fairly high doses and caused reversible dose-related antagonism of chemodepression induced by [Met]enkephalin. It also antagonized depression caused by single doses of [Leu]enkephalin, [D-Ala2, D-Leu5]enkephalin, [D-Ala2, Me-Phe4, Gly-ol5]enkephalin or dynorphin (1-8). ICI 174864, a more potent and selective delta-opioid receptor antagonist, also antagonized chemodepression induced by [Met]enkephalin or by the selective delta-receptor agonist [D-Pen2, D-Pen5]enkephalin. Comparison of background or 'spontaneous' chemosensory discharge during the 30 min periods immediately before and after injecting ICI 174864 (0.1-0.2 mg kg-1 i.c.) showed a significant increase in discharge in one experiment, but in four others discharge was either unaffected or decreased after the antagonist, which argues against a toxic depression of chemosensors by endogenous opioids under resting conditions in our preparation. Sensitivity of the carotid chemoreceptors to hypoxia (ventilating with 10% O2) was increased significantly after ICI 174864, which could be taken as evidence that endogenous opioids depress chemosensitivity during hypoxia. In contrast, responsiveness to hypercapnia was reduced after the antagonist, implying that endogenous opioids may potentiate chemoreceptor sensitivity during hypercapnia. The results obtained using 'selective' agonists and antagonists provide evidence that depression of chemosensory discharge caused by injected opioids involves a delta type of opioid receptor within the cat carotid body. Endogenous opioids may modulate arterial chemoreceptor sensitivity to physiological stimuli such as hypoxia and hypercapnia.

Pharmacological characterization of the receptor involved in chemoexcitation induced by adenosine.

Experiments were performed on cats anaesthetized with pentobarbitone in which carotid body chemoreceptor activity was recorded from the peripheral end of a sectioned carotid nerve. Intracarotid (i.c.) injections of adenosine and its analogues, NECA (5'-N-ethylcarboxamidoadenosine), L-PIA(L-N6-phenylisopropyladenosine), and D-PIA(D-N6-phenylisopropyladenosine), caused dose-related increases in chemosensory discharge. The rank order of potency as chemoreceptor stimulants was: NECA greater than adenosine greater than L-PIA greater than D-PIA. Infusion of theophylline antagonized the chemoexcitatory effects of NECA, and infusion of 8-phenyltheophylline (8-PT), which is a more potent adenosine antagonist with less activity as a phosphodiesterase inhibitor, reduced the chemoexcitation induced by adenosine. Infusion of 8-PT (10 micrograms min-1 i.c.), a dose which substantially reduced the effect of injected adenosine, also reduced the sensitivity of carotid chemoreceptors to hypoxia (10% O2 for 4 min). It is concluded that the adenosine receptors in the cat carotid body which mediate chemosensory excitation are xanthine-sensitive and appear to be of the A2 sub-type. Adenosine, released within the carotid body by physiological stimuli, may be involved in chemoexcitation.

Anandamide induces cardiovascular and respiratory reflexes via vasosensory nerves in the anaesthetized rat.

1. We tested the hypothesis that sensory nerves innervating blood vessels play a role in the local and systemic regulation of the cardiovascular and respiratory (CVR) systems. We measured CVR reflexes evoked by administration of anandamide (86 - 863 nmoles) and capsaicin (0.3 - 10 nmoles) into the hindlimb vasculature of anaesthetized rats. 2. Anandamide and capsaicin each caused a rapid dose-dependent reflex fall in blood pressure and an increase in ventilation when injected intra-arterially into the hindlimb. 3. Action of both agonists at the vanilloid receptor (VR1) on perivascular sensory nerves was investigated using capsazepine (1 mg kg(-1) i.a.) a competitive VR1 antagonist, ruthenium red (1 mg kg(-1) i.a.), a non-competitive antagonist at VR1, or a desensitizing dose of capsaicin (200 nmoles i.a.). The cannabinoid receptor antagonist SR141716 (1 mg kg(-1) i.a.) was used to determine agonist activity at the CB(1) receptor. 4. Capsazepine, ruthenium red, or acute VR1 desensitization by capsaicin-pretreatment, markedly attenuated the reflex CVR responses evoked by anandamide and capsaicin (P< 0.05; paired Student's t-test). Blockade of CB(1) had no significant effect on the responses to anandamide. 5. Local sectioning of the femoral and sciatic nerves attenuated CVR responses to anandamide and capsaicin (P< 0.05). Vagotomy or carotid sinus sectioning had no significant effect on anandamide- or capsaicin-induced responses. 6. These data demonstrate that both the endogenous cannabinoid, anandamide, and the vanilloid, capsaicin, evoke CVR reflexes when injected intra-arterially into the rat hindlimb. These responses appear to be mediated reflexly via VR1 located on sensory nerve endings within the hindlimb vasculature.

On the specificity and type of receptor involved in carotid body chemoreceptor activation by adenosine in the cat.

Experiments were performed on cats anaesthetized with pentobarbitone in which carotid chemoreceptor activity was recorded from the peripheral end of a sectioned carotid sinus nerve. Intracarotid injections of adenosine 5'-triphosphate (ATP) (1-100 micrograms i.c.) caused a dose-related increase in chemosensory discharge which was delayed in onset. The adenosine uptake inhibitor dipyridamole potentiated the chemoexcitatory effects of injected adenosine and ATP. The stable ATP analogue alpha-beta-methylene ATP (10-100 micrograms i.c.) depressed chemoreceptor discharge, which suggests the presence of a P2-purinoceptor in the carotid body, and provides evidence that the chemoexcitatory effect of ATP results from its hydrolysis to adenosine 5'-phosphate (AMP)/adenosine. Adenine, inosine, guanosine, cytidine and uridine had no appreciable effect on chemoreceptor discharge. The adenosine R-site agonists 2'-chloroadenosine and N6-methyladenosine had chemoexcitatory effects which were similar to those of adenosine, whereas the P-site agonist 2'-deoxyadenosine had no appreciable effect on discharge. We conclude that the adenosine receptor in the cat carotid body has some of the characteristics of an R-site receptor according to the classification of Londos & Wolff (1977).

Effect of adenosine on carotid chemoreceptor activity in the cat.

1 The effects of intracarotid (i.c.) injections or infusions of adenosine on chemoreceptor activity recorded from the peripheral end of a sectioned carotid sinus nerve have been studied in cats anaesthetized with pentobarbitone. 2 Adenosine injections (0.1-100 micrograms) caused a rapid and marked increase of spontaneous chemoreceptor discharge, the intensity, duration and onset of which was dose-dependent. Infusion of adenosine, 50 microgram/min, also evoked an increase in discharge which persisted for the duration of the infusion. 3 Both theophylline (1 mg i.c.) and aminophylline (1 mg i.c.) caused short-lasting decreases in spontaneous discharge but did not prevent the excitatory effect of adenosine. Theophylline increased the excitatory action of adenosine. 4 Naloxone (400 micrograms i.c.) antagonized the depressant effect of morphine on chemoreceptor discharge but not the excitatory action of adenosine. 5 It is concluded that exogenous adenosine can excite the cat carotid chemoreceptors, an effect which is not prevented by theophylline in the doses studied. The physiological significance of the findings is discussed.

Changes in carotid body amine levels and effects of dopamine on respiration in rats treated neonatally with capsaicin.

Dopamine levels in rat carotid bodies and the effects of intravenous dopamine injections on respiration in adult rats anaesthetized with pentobarbitone have been studied in animals which were treated with capsaicin neonatally. Levels of dopamine were five fold higher in the carotid bodies of capsaicin-treated rats as compared with vehicle-treated controls, but there was no significant difference between capsaicin-treated and vehicle-treated rats in their ID50 values for dopamine-induced respiratory depression. Domperidone, a dopamine D2-receptor antagonist, substantially reduced the respiratory depression caused by dopamine, both in capsaicin-treated and in control animals, suggesting that a D2-receptor was involved in the response. Cutting the carotid sinus nerves greatly reduced the ventilatory-depressant effect of dopamine, showing that sensory receptors, most probably arterial chemoreceptors, were responsible for most of the response. Substantially less reflex hyperventilation was evoked in capsaicin-treated rats by the peripheral chemoreceptor stimulants hypoxia and sodium cyanide, in comparison with the controls, and domperidone did not increase the responsiveness. About 80% of the reflex ventilatory change originated from carotid body chemoreceptors. The hypoventilation caused by breathing 100% O2 was not significantly different in capsaicin-treated rats when compared with controls. Domperidone substantially reduced this response in capsaicin-treated rats, but not in vehicle-treated animals. Dopamine-induced respiratory depression in capsaicin-treated rats was slightly enhanced, rather than reduced, by oxygen breathing; domperidone remained an effective antagonist of dopamine-induced ventilatory depression. Most of the reduction in respiration caused by dopamine in rats anaesthetized with pentobarbitone can be attributed to actions on a dopamine D2-receptor located in the carotid body. However, despite the increased levels of dopamine found in the carotid bodies, the reduced peripheral chemosensitivity observed in anaesthetized capsaicin-treated rats does not appear to result from a change in sensitivity to dopamine.

Effects of the antagonists MDL 72222 and ketanserin on responses of cat carotid body chemoreceptors to 5-hydroxytryptamine.

The effects of intracarotid (i.c.) injections of 5-hydroxytryptamine (5-HT; 1-50 micrograms) on carotid chemoreceptor activity recorded from the carotid sinus nerve have been studied in anaesthetized cats. Three separate components in the complex response of the chemoreceptors to injected 5-HT were identified. Firstly, a transient burst of activity was obtained during the injection period in 56% of the recordings. Secondly, in all the recordings a period of chemodepression commenced a few seconds after completing the injection and was usually dose-related. Thirdly, a delayed longer-lasting chemoexcitation occurred in many experiments, concomitant with a fall in systemic blood pressure. The neuronal 5-HT receptor antagonist MDL 72222 (10-100 micrograms kg-1, i.c.) virtually abolished the transient chemoexcitation evoked during 5-HT injections and also significantly increased the mean ID50 for 5-HT-induced chemodepression; in 37% of recordings 5-HT caused a dose-related chemoexcitation after the high dose of MDL 72222. Neither the delayed chemoexcitation nor the hypotension caused by 5-HT were much affected by the antagonist. MDL 72222 itself had a biphasic effect on chemosensory discharge, causing depression followed by a delayed excitation. The 5-HT2-receptor antagonist ketanserin (100 micrograms kg-1, i.c.) had no appreciable effect on the transient chemoexcitation evoked during 5-HT injections and caused a slight but significant increase in the mean ID50 for 5-HT-induced chemodepression. The delayed chemoexcitation and accompanying hypotension associated with 5-HT were both substantially reduced or abolished by the antagonist. Ketanserin itself caused a short-lasting period of chemoexcitation. All the effects of injected 5-HT on chemosensory discharge could be abolished by the combination of MDL 72222 and ketanserin (100 micrograms kg-1, i.c.). Neither MDL 72222 nor ketanserin had any significant effect upon the response of the carotid chemoreceptors to hypoxia. The rate at which discharge increased, and also the steady-state discharge before and during hypoxia, were unaffected by the antagonists, alone or in combination. At least two types of 5-HT receptor appeared to be involved in the response of carotid body chemoreceptors to 5-HT. Transient excitation and chemodepression were mediated via MDL 72222-sensitive (peripheral neuronal) receptors whereas the delayed chemoexcitation and associated hypotension involved a ketanserin-sensitive, presumably 5-HT2-, receptor. It appears unlikely that 5-HT plays a crucial role in chemoreception.