Biomedical subjects

A Arce

Publications and source records attributed to A Arce.

At least 55 records · Page 3Linked to original sources

PubMed1997

Twenty-four-hour rhythms of serum ACTH, prolactin, growth hormone, and thyroid-stimulating hormone, and of median-eminence norepinephrine, dopamine, and serotonin, in rats injected with Freund's adjuvant.

The effect of Freund's adjuvant injection on 24-h variation of circulating ACTH, prolactin, growth hormone (GH), and thyroid-stimulating hormone (TSH) levels, and of norepinephrine (NE) content, and dopamine (DA) and serotonin (5HT) turnover in median eminence, was examined in adult rats kept under light between 0800 and 2000 h daily. Groups of 6-10 animals received Freund's complete adjuvant or its vehicle at 1100 h 3 days before sacrifice and were killed by decapitation at six different time intervals throughout a 24-h cycle. In rats injected with adjuvant's vehicle, serum ACTH and prolactin exhibited peak values around the light-dark transition (p < 0.0001 and < 0.04, respectively), while the maximum in TSH was found in the late afternoon (p < 0.0001, one-way ANOVA). GH levels did not vary on a 24-h basis. In Freund's adjuvant-injected rats, 24-h variations of TSH levels became blunted, while 24-h variations of prolactin and ACTH persisted. Freund's adjuvant augmented serum ACTH and prolactin levels, and decreased GH and TSH levels (p < 0.0007, factorial ANOVA). Median-eminence NE content, and turnover of DA, assessed by measuring dihydroxyphenylacetic acid, DOPAC/DA ratio, and of 5HT, assessed by measuring 5-hydroxyindoleacetic acid, HIAA/5HT ratio, varied on a 24-h basis in rats receiving adjuvant's vehicle (p < 0.02). Median-eminence NE content attained its maximum at 1600-2000 h, while maxima in DOPA/DA and HIAA/5HT ratios occurred at 0400 h. Injection with Freund's adjuvant reduced the amplitude of the daily variation of NE content, shifted the maximum of DOPAC/DA ratio toward the light-dark transition, and blunted the daily variation in HIAA/5HT ratio in median eminence. The administration at 1200 of the immunosuppressant drug cyclosporine (5 mg/kg, 5 days) restored the augmented ACTH and prolactin levels (p < 0.0001, factorial ANOVA) and depressed GH and TSH levels (p < 0.02) found in Freund's adjuvant-injected rats. Cyclosporine was also effective in restoring 24-h rhythmicity of serum ACTH and TSH, but not of prolactin, levels. Cyclosporine did not modify the effect of Freund's adjuvant on time-of-day changes of median-eminence NE content, but it was effective in counteracting the changes of DA and 5HT turnover found after immunization. The results are compatible with a significant effect of immune-mediated inflammatory response at an early phase after Freund's adjuvant injection on ACTH, GH, prolactin, and TSH release, which is partially sensitive to immunosuppression by cyclosporine.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Twenty-four-hour rhythms in immune responses in rat submaxillary lymph nodes and spleen: effect of cyclosporine.

Twenty-four-hour variations in cellularity, lipopolysaccharide (LPS)- and concanavalin A (Con A)-induced cell proliferation, and natural killer (NK) activity were examined in submaxillary lymph nodes and spleen of rats injected with Freund's complete adjuvant or its vehicle and kept under light from 08:00 to 20:00 h daily. A significant daily variation in cellularity was detected, exhibiting maxima at 09:00 h in submaxillary lymph nodes (nonimmunized and immunized rats) and at 13:00 h in spleen (immunized rats only). Submaxillary lymph node LPS- and Con A-mitogenic effect displayed maximal activity during daytime (peak at 13:00-17:00 h). In spleen, the maxima for 24-h rhythm in LPS-induced cell proliferation and NK activity occurred at midnight and at early morning (09:00 h), respectively. Con A-induced spleen cell proliferation peaked at midday in nonimmunized rats only. Injection of the immunosuppressive drug cyclosporine decreased Freund's adjuvant-induced augmentation of LPS and Con A mitogenic effect in both tissues and diminished spleen cell number. Cyclosporine blunted circadian rhythms in submaxillary lymph node Con A response and cell number, while it shifted the maximum in LPS effect to peak at 01:00 h. Cyclosporine also suppressed the circadian changes in LPS- and Con A-induced spleen cell proliferation, but not those found in NK activity. The results indicate the existence of 24-h rhythms in immune responses of rat submaxillary lymph nodes and spleen with maxima at different times of the day and that were significantly affected by cyclosporine injection.

Animals↗

PubMed1996

Changes in mediobasal hypothalamic dopamine and indoleamine metabolism after superior cervical ganglionectomy of rats.

Eight days after bilateral superior cervical ganglionectomy (Gx) of rats, norepinephrine content of medial basal hypothalamus (MBH) decreased significantly by 44-50%. To obtain information on other possible neurochemical sequela of Gx in MBH, we examined the metabolism of dopamine and serotonin in MBH of Gx rats by employing a high pressure liquid chromatography procedure. Eight days after Gx, MBH dopamine levels augmented significantly. Assessment of dopamine metabolism by measuring dihydroxyphenylacetic acid (DOPAC)/dopamine and homovanillic acid (HVA)/dopamine indexes indicated a significant decrease of MBH DOPAC/dopamine ratio after Gx. MBH serotonin levels increased, and 5-hydroxyindoleacetic acid (5-HIAA)/serotonin index decreased significantly in Gx rats. To examine the interaction Gx-induced changes on MBH dopamine and serotonin with the modified hormonal milieu produced by an ectopic pituitary transplant, adult male rats bearing an ectopic pituitary within the pectoral muscles from day 5 of life were submitted to Gx on day 60 of life and were studied 8 days later. MBH dopamine content increased significantly after pituitary grafting, an effect counteracted by a subsequent Gx, while Gx alone augmented MBH dopamine levels. DOPAC and HVA contents augmented in pituitary-grafted animals, an effect counteracted by Gx. Gx increased MBH serotonin content in control but not in pituitary-grafted rats. After pituitary grafting a decrease in MBH 5-HIAA levels was found, an effect reversed by Gx. Pituitary transplants brought about a significant increase of MBH DOPAC/dopamine index, and a significant decrease in 5-HIAA/serotonin index, both effects being counteracted by Gx. Gx of control rats resulted in a significant decrease of MBH 5-HIAA/serotonin index. Analyzed as a main effect in a factorial analysis of variance, Gx decreased MBH DOPAC/dopamine and HVA/dopamine indexes significantly. Plasma prolactin increased in pituitary-grafted rats, an effect further increased by a subsequent Gx. In pituitary-grafted, Gx rats plasma GH levels augmented significantly. The data suggest that superior cervical ganglion removal affects differentially dopamine and indoleamine metabolism in MBH of control and pituitary-grafted rats.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1996

Benzodiazepine receptors increase induced by stress and maze-learning performance in chick forebrain.

Two-day-old chicks were selected on their second escape performance in a one-trial, maze-learning task, and termed high-performance (H-P), moderate-performance (M-P), and low-performance (L-P) chicks. The learning degree was expressed by the escape time improvement being respectively the 64, 46, and 24%. Then, the three selected groups were maintained to reach 15 days of age and then submitted to acute swimming stress, and [3H]flunitrazepam and [3H]Ro 5-4864 receptor bindings were performed on synaptosomal/mitochondrial membranes from forebrain. The receptor number for both radioligands in stressed high-performance chicks was significantly higher than in stressed low-performance chicks. The results suggest that higher performance chicks were more susceptible than lower performance chicks to acute stress associated to increase of both central and peripheral type benzodiazepine receptors, probably due to differences in the degree of endogenous emotionality.

Animals↗

PubMed1996

Recruitment of peripheral-type benzodiazepine receptors after acute stress in chick forebrain membranes: action of Triton X-100.

A significant increase in the number of measurable [3H]Ro 5-4864 receptors was found in forebrain membranes of chicks submitted to 15 min of acute swim stress compared to non-stressed chicks. In addition, low subsolubilizing concentrations of Triton X-100 caused a significant increase in the measurable [3H]Ro 5-4864 receptor number in forebrain membranes from non-stressed chicks. However, this increase caused by Triton X-100 was not observed when tested in forebrain membranes from stressed chicks. In all cases the affinity remained unchanged. These results suggest that: (1) acute stress and Triton X-100 induce receptor increase by enhancing [3H]Ro 5-4864 accessibility to a pool of receptors not detected before stress or in the absence of detergent; (2) the pool of non-measured receptors represents about a third of the total in control chicks; (3) the increments are not additive and could involve receptors coming from the same non-measured pool; (4) the receptor increase during a short time of stress could be explained by recruitment of receptors but not by an increase in the receptor protein biosynthesis; (5) stress induces a maximal recruitment of measurable [-3H]Ro 5-4864 receptors.

Animals↗

PubMed1996

Estimation of the binding affinity constants of soluble ligand-receptor complexes by a rapid filtration technique: [3H]-flunitrazepam-bovine serum albumin as an example.

A method for determining the equilibrium dissociation constant (KA) of a soluble ligand (L) from a soluble receptor (A) in the presence of another solid phase receptor (R) for the same ligand was developed. The total and nonspecific binding of L to R was measured in the presence and in the absence of A. The separation of bound and free L was done by a rapid filtration technique so that only the complex RL, but not AL, was recovered. An apparent dissociation constant (KR,app) was calculated from the saturation curve obtained in the presence of A. The magnitude of KA could be determined from this KR,app and the value of the equilibrium dissociation constant of the complex R-L (KR) calculated from the saturation curve in the absence of A. The equality of the Bmax values obtained in the presence and in the absence of A assured the accuracy in the determination of KA so that the fulfillment of this condition could be used as an internal control. For the correct definition of nonspecific binding, the displacement agent (L1) should be used at concentrations within the range 10(2).KR < L1 < 10. K4. This fact constraints the applicability of the method to systems where KA/KR > 10(3). The highest sensitivity of the method can be attained when 0.33 < [At]/KA < 3. The equilibrium binding constant of [3H]-flunitrazepam to non-delipidized bovine serum albumin determined by the present approach (31 +/- 7 mumol/L) did not differ significantly from the literature.

Binding Sites↗

PubMed1995

Effect of stress and cyclosporine on ornithine decarboxylase activity in rat submaxillary lymph nodes.

This study was performed: (1) to assess whether the stress produced in rats by daily turpentine oil injections for 5 days, or by restraining the animals for 30 min during 5 days, affected basal and Freund's adjuvant-stimulated submaxillary lymph node ornithine decarboxylase activity, an indicator of cell proliferation; (2) to analyze whether the activity of the immunosuppressive drug cyclosporine on submaxillary lymph node ornithine decarboxylase activation after Freund's adjuvant injection was modified in stressed rats; (3) to examine the mediation of stress effects on submaxillary lymph node ornithine decarboxylase activation by regional sympathetic or parasympathetic nerves. Animals subjected to a unilateral superior cervical ganglionectomy, or to a unilateral chorda tympani section, together with a contralateral sham-operation were employed. After turpentine oil or restraint stress, a significant decrease in submaxillary lymph node ornithine decarboxylase was found. A unilateral sympathetic denervation of submaxillary lymph nodes counteracted in part the inhibitory effect of stress on ornithine decarboxylase activation, as well as augmented the enzyme response in innervated submaxillary lymph nodes. Ornithine decarboxylase activation attained similar values in parasympathetic decentralized or intact submaxillary lymph nodes and the unilateral parasympathetic decentralization did not interfere with the inhibition of enzyme activity found in turpentine oil-stressed rats. Cyclosporine administration (5 or 20 mg/kg) significantly decreased Freund's adjuvant-induced ornithine decarboxylase activity in the submaxillary lymph nodes of control rats, but failed to modify it in turpentine oil-stressed animals. In this latter group, a higher (40 mg/kg) dose of cyclosporine decreased ornithine decarboxylase activity on the innervated side only. A diminished inhibitory response to cyclosporine was found in the parasympathetic decentralized submaxillary lymph nodes of unstressed rats. The results support the view that the immunosuppressive effects of cyclosporine may diminish during stress, in part due to changes in the traffic of neural signals in local sympathetic nerves.

Animals↗

PubMed1995

Cyclosporine effects on in vitro responsiveness of anterior pituitary hormone release to dopamine and thyrotropin-releasing hormone in young female rats.

Endocrine side effects of the immunosuppressive drug cyclosporine (CyA) include changes in anterior pituitary hormone secretion. The aim of the present study was to examine the effects of CyA on the responsiveness of in situ and ectopic anterior pituitary prolactin (PRL), growth hormone (GH) and luteinizing hormone (LH) release response to dopamine (DA) and thyrotropin-releasing hormone (TRH) treatment in young female rats, and to evaluate the possible PRL participation in these effects. Thirty day old rats were rendered hyperprolactinemic by transplanting an anterior pituitary gland of a littermate donor, under the kidney capsule, and were then injected with CyA or vehicle for 2 or 8 days. Sham-operated rats were used as controls and treated in the same way. CyA treatment prevented the increase in plasma PRL levels which occurred in controls after pituitary grafting. In vitro basal PRL release of in situ pituitaries from either sham-operated and/or pituitary-grafted animals was decreased by CyA treatment at any point studied. Basal in vitro secretion of GH was only decreased in the in situ pituitaries from grafted animals after 2 days of CyA therapy. The presence of an ectopic pituitary lead to an increase in the in vitro basal LH secretion from in situ pituitaries as compared to those from sham-operated rats. Basal LH release rates were not changed by CyA treatment, although the LH release in vitro did increase in the in situ pituitaries from sham-operated animals treated with the drug for 2 days. DA addition to the incubation media decreased the in vitro release of PRL, GH and LH from the in situ pituitaries of sham-operated and pituitary-grafted animals treated with vehicle. In CyA treated animals, DA decreased in vitro PRL release from the in situ pituitaries of animals, independently of the presence or absence of an ectopic pituitary. Reductions of the in vitro GH and LH release release after DA treatment were higher in the in situ pituitaries from grafted animals on day 8 of CyA or vehicle treatment. TRH increased the in vitro release of the three hormones with differential effects related to the length of the treatment with CyA and/or the presence of an ectopic pituitary. In vitro release of PRL and GH by ectopic pituitaries was inhibited by previous treatment with CyA and this effect was decreased proportional to the duration of the treatment with the drug, while LH secretion was not modified. Addition of DA to the incubation media resulted in a marked reduction of in vitro PRL and GH release, but only at day 8 of vehicle treatment on GH release did DA addition to media further decrease the release of both hormones from ectopic pituitaries from animals treated for 2 or 8 days with the drug, whereas LH secretion was not modified. TRH addition to the incubation media of ectopic pituitaries surprisingly reduced PRL and GH secretion on day 8 of CyA treatment or after surgery. The results of these studies suggest that CyA can act directly at the hypophyseal level modifying pituitary responsiveness to external stimuli. CyA seems to exert its main effects on lactotroph activity while its effects on somatotrophs and gonadotrophs are less.

Animals↗

PubMed1995

Effects of cyclosporine at the hypothalamic-pituitary axis in pituitary-grafted young female rats.

This work was designed to investigate the effects of cyclosporine on prolactin secretion by an ectopically grafted heterologous pituitary gland, and on the hypothalamic content of norepinephrine, dopamine and serotonin. The administration of cyclosporine prevented the augmentation in plasma prolactin levels which occurred following an ectopic graft of a litter-mate pituitary gland. In contrast, in sham-operated rats, cyclosporine increased prolactin levels on day 8 of treatment. Both pituitary grafting and cyclosporine treatment in sham-operated rats decreased hypothalamic norepinephrine content. In grafted rats, cyclosporine returned hypothalamic norepinephrine to normal. Hypothalamic serotonin content decreased 8 days after pituitary grafting but increased to the values of control animals after cyclosporine administration. Cyclosporine treatment for 2 and 8 days increased serotonin content in sham-operated animals. As expected, the hypothalamic dihydroxphenylacetic acid/dopamine index increased after pituitary grafting and administration of cyclosporine for 8 days resulted in a further increase. Cyclosporine administration for 2 days, however, decreased this index to the values observed in control animals while drug treatment of control rats for 8 days decreased the dihydroxyphenylacetic acid/dopamine index. In vitro release of prolactin from the ectopic gland was markedly decreased in animals treated with cyclosporine for 2 days and this effect was less evident in 8-day treated rats.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Dihydroxyphenylacetic Acid↗

PubMed1994

Chick imprinting performance and susceptibility to acute stress associated to flunitrazepam receptor increase.

One-day-old chicks were selected on their performance in imprinting behaviour and termed high-imprinted (H-I), partially imprinted (P-I) and low-imprinted (L-I) chicks. Then, H-I and L-I chicks were submitted to acute handling stress and [3H]flunitrazepam receptor-binding was performed on synaptosomal membranes from forebrain at various times after handling. The receptor number significantly increased in L-I but not in H-I chicks at 30 min after handling while the affinity remained unchanged at all times. In addition, when the three selected groups were maintained to reach 15 days of age and then they were submitted to acute swimming stress, the degree of receptor increase was also inversely related to the degree of imprinting performance. The receptor increase associated to swimming stress was higher in the left hemisphere, suggesting an interhemispheric asymmetry of stress effects. The results suggest that more-imprinted chicks are less susceptible than less-imprinted chicks to acute stress associated to central benzodiazepine receptor increase, probably due to differences in the degree of endogenous emotionality.

Animals↗

PubMed1994

Acute ethanol administration in diestrus-2 in the rat on pulsatile prolactin and LH release.

Exposure to ethanol is followed by changes in reproductive function in man and animals, characterized by modifications in the secretion patterns of prolactin and luteinizing hormone (LH). As both hormones are secreted in an episodic fashion, the present work was undertaken to study the effects of acute ethanol administration on pulsatile prolactin and LH secretion patterns in adult female rats. Rats were previously cannulated to allow a continuous blood withdrawal to study the pulsatile patterns of prolactin and LH. The mean values of prolactin during the bleeding period and the absolute pulse amplitude of prolactin peaks were significantly increased by acute ethanol administration, whereas a significant decrease of relative pulse amplitude and frequency of this hormone was observed. On the other hand, ethanol administration increased the mean serum LH levels and the absolute and relative amplitudes of LH peaks. Ethanol treatment did not modify either frequency or duration of LH peaks. These data suggest that acute ethanol administration in adult female rats is followed by changes in the pulsatile prolactin and LH secretory patterns, which might be part of the mechanism to explain ethanol effects on the endocrine system.

Animals↗

PubMed1994

Piribedil affects dopamine turnover in cochleas stimulated by white noise.

The presence of dopamine (DA) within the cochlea has been previously reported, indicating that its turnover increases under noise stimulation. In the present report, piribedil, a dopaminergic D2 agonist, was used in order to provide evidence of the activity of D2 receptors in the turnover of DA under noise stimulation. Long-Evans rats were intraperitoneally injected with distilled water or with a solution of piribedil one hour previously to either noise or silence exposure. Noise stimulation was performed in an anechoic chamber at 70, 90 or 110 dB SPL for one hour. The animals were then sacrificed and the cochlear contents of DA and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were quantified by HPLC with electrochemical detection. The administration of piribedil to animals kept in silence did not modify the cochlear DA, DOPAC and HVA content. Noise stimulation resulted in a decrease of the cochlear DA content and an increase of the cochlear DOPAC and HVA contents in vehicle treated animals. The administration of piribedil resulted in a blockade of this noise induced cochlear DA turnover. These results suggest that piribedil stimulates cochlear D2 receptors controlling the cochlear DA release. Piribedil action on D2 receptors could explain the improvement observed in some cochleo-vestibular diseases signs after piribedil treatment.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1994

Tardive akathisia due to sulpiride.

A 56 year-old woman who suffered from parkinsonism, oro-lingual dyskinesia (OLD) and tardive akathisia (TA) due to sulpiride is reported. OLD and TA appeared after sulpiride withdrawal. The patient was successfully treated with tetrabenazine even a mild parkinsonism was present. TA seems to be related with an apparent dopaminergic hyperactivity and it has to be differentiated of other neuroleptic-induced movement disorders such as restless legs syndrome in order of an appropriate treatment. Sulpiride has the same possible side effects than classic neuroleptics.

Akathisia, Drug-Induced↗

PubMed1994

Transient benzodiazepine-GABAA receptor increase after a passive avoidance learning in synaptosomal membranes from chick forebrain.

One-day-old chicks were exposed to a one-time passive avoidance learning task. After chicks peak a bead dipped in a bitter-tasting liquid, they learn to stop pecking the bead. Radioligand binding analysis of [3H]flunitrazepam was performed on crude synaptosomal membranes from forebrains, at 10, 30, and 60 min post-training. Water-trained chicks (control) pecked a bead dipped in water, and they did not learn to stop pecking the bead. The water control was complemented with a methyl anthranilate fed control chick to demonstrate that taste per se does not affect the [3H]flunitrazepam binding. At 30 min in relation to 10 min post-training, the Bmax increased 31% in water-trained chicks and 56% in taste-trained chicks, with Bmax of the taste-trained chicks reaching a value 22% higher than that in water-trained chicks. The difference, attributable to the learning, disappeared at 60 min post-training, and at all times the affinity remained unchanged. The Bmax increase in water-trained chicks might be attributable to psychological stress accompanying the task and the Bmax increase in taste-trained chicks attributable to the learning in addition to the stress accompanying the task. The results suggest that the receptor increase associated with learning is involved in early stages of memory formation.

Animals↗

PubMed1994

Thyroid hormones modulate both adenosine transport and adenosine A1 receptors in rat brain.

Adenosine transport and adenosine A1 receptors in rat brain are subjected to regulation by thyroid hormone levels. The studies were carried out with brain stem synaptosomal preparations from rat brain in euthyroid and various hypothyroid situations. The maximum velocity of the nitrobenzylthioinosine (NBTI)-sensitive adenosine transport was 3.3 +/- 0.3 pmol.mg protein-1.s-1 in euthyroid rats. The transport in 1-wk thyroidectomized rats was decreased by 45.8% with respect to controls. No changes were found in the affinity of euthyroid and hypothyroid rats, with the Michaelis-Menten constant values equal to 1.9 +/- 0.9 and 2.0 +/- 0.5 microM, respectively. The transporter number measured by NBTI binding also decreased; the maximum binding capacity (Bmax) was 112.9 +/- 21.9 and 31.3 +/- 4.1 fmol/mg protein for euthyroid and hypothyroid rats, respectively. The adenosine A1 receptors were measured in synaptosomal membrane preparations in the presence of 100 microM guanosine-5'-O-3-thiotriphosphate for cylopenthyl-1,3-dipropylxanthine 8-[dipropyl 2,3-3H(N)] ([3H]DPCPX) binding. In euthyroid rats, the Bmax value was 227.6 +/- 27.6 fmol/mg protein, a significant decrease of 23% was obtained in 1-wk hypothyroid rats. In all other thyroid situations studied, adenosine transport capacity, adenosine transporter number, and adenosine A1 receptor number were restored to control levels.

Adenosine↗

PubMed1994

Changes in serum growth hormone and prolactin levels, and in hypothalamic growth hormone-releasing hormone, thyrotropin-releasing hormone and somatostatin content, after superior cervical sympathectomy in rats.

After bilateral superior cervical ganglionectomy (SCGx) of adult male rats, norepinephrine (NE) content of the medial basal hypothalamus (MBH) decreased significantly by 39-47% from 16 h to 7 days after surgery. During this time the levels of serum growth hormone (GH) and prolactin (PRL) and of MBH GH-releasing hormone (GRH), thyrotropin-releasing hormone (TRH) and somatostatin were measured by RIA. In sham-operated controls, serum PRL increased and serum GH decreased 16-24 h after surgery, attaining pre-surgical levels later on. In SCGx rats, significantly lower serum GH and PRL and higher MBH GRH and TRH content as compared to controls was observed 16-24 h after surgery, during the wallerian degeneration phase after SCGx. MBH somatostatin concentration decreased in SCGx rats 20 h after surgery. Two injections of the alpha 1-adrenoceptor blocker prazosin 45 and 90 min before sacrifice, alone or together with the beta-blocker propranolol, prevented the changes in MBH hypophysiotropic hormone content, as well as in serum GH and PRL levels, found in SCGx rats 20 h after surgery. Propranolol treatment did not affect hormone levels. Neither drug modified the decrease in MBH NE content observed after SCGx. The results argue in favor of the existence of physiologically relevant projections from superior cervical ganglion neurons to the MBH controlling hypophysiotropic hormone release.

Animals↗

PubMed1993

Effects of noise stimulation on cochlear dopamine metabolism.

Dopamine (DA) appears to be one of the putative neurotransmitters of the lateral efferent olivocochlear fibers. However, its role in the cochlear physiology remains unknown. In this study, animals were exposed for 1 h to white noise at 70, 90 or 110 dB SPL or were kept in silence conditions. Afterwards, the cochlear content of DA and its metabolites dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were analyzed using HPLC coupled to electrochemical detection. Cochlear DA concentration decreased with the noise intensity, while cochlear DOPAC and HVA concentrations increased. Males presented higher cochlear DOPAC contents and lower HVA contents than females. This sexual dimorphism could be related to the link between DA and gonadal steroids. Present results show that DA, as other lateral efferent neurotransmitters, is released and metabolized in relationship with the noise stimulation, and suggest that DA could be involved in the modulation of the type I afferent fiber activity.

3,4-Dihydroxyphenylacetic Acid↗

PubMed1992

Benzodiazepine receptor recruitment after acute stress in synaptosomal membranes from forebrain of young chicks: action of Triton X-100.

In young chicks submitted to acute stress by forced swimming there was a significant increase in the number of the measurable [3H]-flunitrazepam receptors in synaptosomal membranes from forebrain. In addition, low subsolubilizing concentrations of Triton X-100 caused a significant increase in the measurable [3H]-flunitrazepam receptor number in synaptosomal membranes from non-stressed chicks. However, this Triton X-100 stimulatory effect was not observed when tested in synaptosomal membranes from stressed chicks. In all cases the affinity remained unchanged. This result suggest that: (i) acute stress and Triton X-100 induce receptor recruitment by enhancing [3H]-flunitrazepam accessibility to a pool of receptors which is unmeasurable either before stress or in absence of detergent; (ii) neither recruitment types are additive and they involve receptors coming from the same nonmeasurable pool; (iii) stress induces a maximal recruitment of existing benzodiazepine receptors; (iiii) the pool of nonmeasurable receptors represents about a quarter of the total in control chicks. The recruitment at a short time of stress could be interpreted in terms involving internalization; recycling or modulation of receptors but not its biosynthesis or degradation.

Acute Disease↗