摘要:

The spatial and temporal summation of light by the receptive field centre of frog retinal ganglion cells were studied by extracellular recording in the eyecup preparation. The purpose was to quantify how summation changes with the state of light and dark adaptation and to clarify whether changes are due to the transition between rod and cone vision. Spatial summation was found to decrease by 30–50% as the cell was light‐adapted to a threshold some 4 log units above the dark‐adapted one. Temporal summation for threshold responses fell as the power –0.17 of the intensity of an adapting steady background. Neither change was bound to the rod‐cone transition but occurred in the ranges of both receptor types; at equal sensitivities the summation of both receptor systems wa

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08267.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

In lightly anaesthetized rats, the latencies and magnitudes of heat‐evoked withdrawal reflexes from the hindlimb were measured electromyographically. Low‐intensity (20–50μA) stimulation of the nucleus raphe magnus (NRM) resulted in an inhibition of the flexion reflex (commonly referred to as analgesia) as evidenced by increased latency and decreased amplitude. The effect lasted for several minutes after the stimulation was terminated. Following lesions of the dorsolateral funiculus (DLF) at the neural thoracic levels 7–8, baseline latencies were reduced and the effect of the NRM stimulation was abolished. Lesions of the DLF at lumbar level 1 resulted in unaltered baseline latencies with persistence of the inhibitory effect of NRM stimulation.The results of the present experiment show that pathways exerting a tonic inhibition of the withdrawal reflex, and mediating the effect of electrical stimulation from the NRM, descend in the DLF at the thoracic level of the spinal cord. At the lumbar level, there is a shift away from the DLF.The antinociceptive effect of 20μA NRM stimulation was partly reduced by pretreatment with the serotonin synthesis inhibitorpara‐chlorophenylalanine (PCPA) or the opiate naloxone (1 mg kg–1i.v.). In animals pretreated with PCPA, naloxone (1 mg kg–1i.v.) completely abolished the analgesic effect of the stimulation. Thus, both serotonergic and opioid systems may be implicated in mediating the analgesia. With 50μA stimulation the same treatment only partly attenuated the NRM‐induced analgesia, indicating an additional non‐serotonergic and non‐opioid mechanism which requires a higher current intens

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08268.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

We have previously shown that, at least at frequencies of 4 Hz and above, a previous stimulation of the intramural vasoconstrictor nerves facilitates the subsequent reponse so that even maximal contractions can develop during periods of stimulation as short as a few seconds. In the present study the facilitating effect of a continuous nerve stimulation was quantitatively tested on ‘single‐twitch’ responses to individual nerve impulses. Small arteries and veins (150–500μm diameter) from rats were mounted in a myograph at known wall tension, and the intramural nerves were activated at frequencies between 0.1 and 32 Hz. After a period of continuous stimulation the single‐twitch responses could be amplified 10–20 times, depending on frequency and duration of the continuous stimulation. No such amplification was observed after application of exogenous noradrenaline. The results therefore reflect a prejunctional frequency‐dependent potentiating mechanism which can strongly reinforce sympathetic neuroeffector control. Furthermore, combined with previous data concerning adrenergic transmitter release, the present results seem to be more compatible with the view that the quantum of transmitter released from each varicosity upon activation is less than an

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08269.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Increases in plasma noradrenaline (NA) concentration occur during moderate to heavy exercise in man. This study was undertaken to examine the spillover of NA from both resting and contracting skeletal muscle during exercise. Six male subjects performed one‐legged knee‐extension so that all measurements could be made both in the exercising and in the resting leg. Subjects exercised for to min at each of 50% and too% of the peak performance capacity of the leg. Leg blood flow was measured by thermodilution and blood samples were drawn for the determination of plasma NA and adrenaline, first in the resting leg and then in the exercising leg. To calculate NA spillover, the extraction of NA (Nae) or of adrenalin (Ae) is required: Naewas measured by repeating the experiment under constant [3H]NA infusion following a 40‐min rest period. During exercise, NA spillover was significantly larger in the exercising leg than in the resting leg both during 50% and 100% leg exercise. These results suggest that contracting skeletal muscle may contribute to a larger extent than resting skeletal muscle to increasing the level of plasma NA during exercise. Contractile activity may influence the NA spillover from skeletal muscle by a presynaptic and/or postsynaptic influence on the sympathetic nervous activity to this t

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08270.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Neuropeptide Y is co‐stored with noradrenaline in peripheral sympathetic nerves, but is not present in the adrenal chromaffin cells in the pig. Plasma levels of neuropeptide Y‐like immunoreactivity and catecholamines were studied upon haemorrhagic shock in the anaesthetized pig. The animals were bled in two successive steps (30 and 10 ml kg–), resulting in a reduction of the mean arterial blood pressure by 44% and 53 %, respectively. Plasma levels of noradrenaline increased abruptly after the first bleeding from 1.21 ± 0.27 to 26.5 ± 6.3 nmol 1‐1. Plasma neuropeptide Y showed a progressive increase from 62 ± 8 pmol 1–1in the basal state to 365 ± 98 pmol 1–1at 60 min after the first bleeding. After the second bleeding plasma neuropeptide Y and noradrenaline showed a largely parallel increase and finally reached levels of 2524 ± 580 pmol 1–1and 316 ± 117 nmol 1–1, respectively. A veno‐arterial gradient of neuropeptide Y and noradrenaline indicating local release was present over the spleen after both bleeding steps. The overflow of neuropeptide Y was delayed about 15 min compared to noradrenaline after the initial bleeding. Depletion of the neuropeptide Y content after shock in the heart and skeletal muscle supported local release also from these organs. Infusions of neuropeptide Y to obtain similar plasma concentrations as during shock (nM range) caused reduction in blood flow as determined by the radionuclide‐labelled microsphere technique in several organs including spleen and skeletal muscle (threshold response at 319 ± 22 pmol 1–1) but not in heart and brain. In conclusion, both neuropeptide Y and noradrenaline were markedly elevated in plasma upon haemorrhagic shock, suggesting release from sympathetic nerve terminals. Neuropeptide Y could therefore have a role as a sympathetic neurotransmitter, and during severe stress, circulating plasma levels are in the range where vasoconstrictio

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08271.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Six healthy subjects (two female) aged 23–40 years participated in a double‐blind randomized cross‐over study to investigate autonomic mechanisms involved in the chronotropic effect of adenosine in conscious man. Adenosine was infused in increasing doses following saline, propranalol (0.2 mg kg‐1body weight) or propranolol (0.2 mg kg‐1plus atropine (0.04 mg kg‐1). Heart rate and blood pressure were measured supine, on standing and during a Valsalva manoeuvre. Plasma catecholamines were measured in the supine and standing positions. Following saline, adenosine (up to 120μg kg‐1min‐1) caused a dose‐related increase in heart rate (mean±SD maximum increase 18±8 bpm;P<0.01). The change in heart rate with adenosine after propranolol (12±9 bpm;P<0.05) did not differ significantly from the corresponding change following saline but was abolished by propranolol plus atropine, which, in turn, was associated with a mean maximum decrease in heart rate of 5±3 bpm (P<0.01). The increase in heart rate during the initial 30 s on standing was augmented with adenosine compared with saline (16 ± 5 bpm;P<0.01). A significant increase in plasma noradrenaline on standing was also found with adenosine compared with saline (6.37 ± 2.86vs. 4.77 ± 1.79 nmol 1‐1;P<0.05). The heart rate response to the Valsalva manoeuvre was not affected by adenosine. These results suggest that the positive chronotropic effect of infused adenosine in conscious man may in part be caused by an inhibition of cardiac vagal tone. An activation of sympathetic nerve a

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08272.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Breathing response to 12% and 6% O2in N, (at isocapnia) was measured in anaesthetized piglets, 1–5 and 19–25 days old, before and after 3 mg kg‐1i.v. naltrexone. The degree of interaction between the anaesthetic and naltrexone was assessed. At the end of each hypoxic trial, arterial blood was sampled for measurements of pH and gas tensions, (Met)enkephalin‐Arg5‐Phe7, adenosine, noradrenaline and adrenalin. Where‐as respiration in older animals was stimulated by hypoxia, young piglets had a biphasic response with a pronounced ventilatory decrease in response to severe hypoxia (6% O2/N2). In young animals there was a greater ventilatory response with naltrexone than without the drug, and the biphasic hypoxic response was ameliorated or reversed by naltrexone. Levels of adrenalin increased and those of encephalin, adenosine and noradrenaline tended to increase during hypoxia in the younger age group. Levels of adenosine showed significant increase when data from both age groups and levels of hypoxia were pooled. Combined with previously reported physiological evidence regarding adenosine in hypoxic depression, we conclude that the present results are compatible with a role of opioid peptides and adenosine in the early postnatal response

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08273.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

In the present study, using rat hippocampal slices, we have further examined the stimulatory effect ofα1adrenoceptors on the accumulation of cyclic AMP, which is known to depend on calcium and adenosine. The addition of noradrenaline (NA) stimulated the accumulation of [3H]inositol phosphates in [3H]inositol‐treated slices. This effect was shared by carbachol (10–100μmol l‐1) but not by the adenosine receptor agonist 2‐chloroadenosine (100μmol l‐1). The stimulatory effect of theα‐agonists (phenylephrine or NA + propranolol) on cyclic AMP was shared by a diacylglycerol derivative,sn‐1‐oleyl‐2‐acetyl glycerol (OAG), and by the tumour‐promoting phorbol esters phorboldibutyrate (PDiBu) and tetradecanoyl phorbol acetate (TPA). PDiBu caused a translocation of protein kinase C from soluble to particulate fractions. The effects of PDiBu andα‐adrenoceptor stimulation on cyclic AMP were not additive. Surprisingly, carbachol (1–1000μmol l‐1) did not stimulate cyclic AMP accumulation in rat hippocampal slices either in the presence or in the absence of an adenosine receptor agonist.The results are compatible with the opinion that a‐adrenoceptor stimulating drugs enhance the formation of inositol phosphates and diacylglycerol, which synergistically activate protein kinase C, which in turn augments the stimulation of cyclic AMP formation. Thus, a neurotransmitter whose principal biological effect is to stimulate inositol phosphate formation can influence cyclic AMP formation by virtue of an interaction with the actions of the ubiquitous neuromodulator adenosine. The fact that the effect of theα‐receptor stimulation was not mimicked by a muscarinic agonist could indicate that other factors besides activation of inositol phospholipid hydrolys are important

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08274.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

Quantitative pharmacological studies were performed on isolated uterine cervix which was obtained from oophorectomized and oestrogen‐treated rats and therefore showed no spontaneous contractility. The concentration‐response curves to ACh and carbacholine were to a varying degree depressed and right‐shifted in the presence of NA, but not NPY or VIP. The electrically induced cholinergic contraction was potentiated in tissues from animals pretreated with reserpine or 6‐OHDA, but only at high stimulation frequencies. Histochemically, both sympatholytics abolished NA from the cervical fibres, whereas immunoreactive NPY was still encountered. Tyramine in the organ bath reduced the contraction amplitude during electrical nerve stimulation concentration‐dependently by aβ‐adrenoceptor‐sensitive mechanism. In the presence of neostigmine the amplitude was reduced by NA, but not by NPY or VIP, which, on the other hand, had an inhibitory effect in the absence of neostigmine. The results offer further support for the view that, although the cervical smooth muscle cells are equipped with adrenoceptors, the neurogenic motor response at low stimulation frequencies (around 3 Hz) is mainly cholinergic. It appears that neurally released NA is able to influence these muscle cells primarily at high frequencies. There is no clear‐cut evidence that the inhibitory effects of neural NPY or VIP on the cervix of spayed, oestrogen‐treated rats are mediated by postju

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08275.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY

摘要:

The effect of insulin‐like growth factor‐I (IGF‐I) on glucose accumulation, amino acid uptake and incorporation of amino acid into protein was studied in arterial smooth muscle. Accumulation of [14C]glucose, uptake of [14C]α‐aminoisobutyric acid (AIB) and incorporation of [14C]phenylalanine into protein were measured in intima‐media preparations of bovine mesenteric arteries (BMA) incubated with IGF‐I for 2, 4 or 6 h. IGF‐I (2.2 nmol l‐1) increased the accumulation of glucose into BMA after 4 h (P= 0.0079) and 6 h incubation (P= 0.0027) and in a concentration of 22 nmol l‐1also after 2 h (P= 0.015). The uptake of AIB and the incorporation of phenylalanine were increased after 4 h incubation with 2.2 nmol l‐1IGF‐I (P= 0.0045 andP= 0.026, respectively). The effects of IGF‐I on all of the metabolic parameters were dependent on incubation time and concentration of IGF‐I. Concentration‐effect curves were determined for the effect of IGF‐I and also for insulin on glucose accumulation in BMA incubated for 6 h. The concentration‐effect relationships for IGF‐I and insulin were very similar with pD2values of 7.6±0.2 (EC50= 27 nmol l‐1) and 7.5±0.2 (EC50= 34 nmol l‐1), respectively. No additive effect of IGF‐I and insulin in supra‐physiological concentrations (1.0μmol l‐1) could be demonstrated. These results show that IGF‐I has metabolic effects which are similar to the effects of insulin in vascular smooth muscle and suggest that IGF‐I may be of impo

ISSN:0001-6772    

DOI:10.1111/j.1748-1716.1987.tb08276.x

出版商:Blackwell Publishing Ltd    

年代:1987

数据来源: WILEY