DOPA cyclohexyl ester, a DOPA antagonist, blocks the depressor responses elicited by microinjections of nicotine into the nucleus tractus solitarii of rats

Nicotinic cholinergic receptors play a role in cardiovascular regulation in the lower brain stem. Herein, we present evidence that l-3,4-dihydroxyphenylalanine (DOPA), a putative neurotransmitter in the central nervous system, is involved in the depressor response to microinjection of nicotine into the nucleus tractus solitarii (NTS). Microinjection of nicotine into the medial area of the NTS led to decreases in arterial blood pressure and heart rate in anesthetized rats. Mecamylamine, a nicotinic receptor antagonist, microinjected into NTS, blocked the depressor and bradycardic responses to nicotine. Nicotine-induced depressor and bradycardic responses were blocked by DOPA cyclohexyl ester (DOPA CHE), an antagonist for DOPA. DOPA CHE did not modify the action of carbachol on excitatory postsynaptic potential in rat cortical slices. These results suggest that endogenous DOPA is involved in nicotine-induced depressor responses in the NTS of anesthetized rats.     

GABA may function tonically via GABA(A) receptors to inhibit hypotension and bradycardia by L-DOPA microinjected into depressor sites of the nucleus tractus solitarii in anesthetized rats

We have proposed that DOPA is a transmitter of the primary baroreceptor afferents terminating in the rat nucleus tractus solitarii (NTS). GABA is a putative inhibitory neuromodulator for baroreflex inputs in the NTS. GABA may inhibit DOPAergic transmission. Drugs were microinjected into depressor sites of the NTS in anesthetized rats. DOPA (10-60 ng) elicited dose-dependent depressor responses. GABA (3-300 ng) elicited dose-dependent pressor responses. Nipecotic acid (100 ng) elicited pressor responses. Bicuculline (10 ng) elicited depressor responses. Responses to DOPA (30 ng) were inhibited by pretreatment with GABA and nipecotic acid, but potentiated by bicuculline, when vascular responses to pretreated drugs returned to basal levels. DOPA ME, a competitive DOPA antagonist, did not displace specific [3H]GABA binding. Prior DOPA ME (1 microg) inhibited by one-half pressor responses to 300 ng GABA. GABA seems to inhibit tonically via GABA(A) receptors depressor responses to DOPA and to elicit pressor responses partially by inhibition of tonic function of endogenous DOPA to activate depressor sites in the NTS. These findings further support the above proposal.     

Local administration of l-DOPA in the chicken ventromedial hypothalamus increases dopamine release in a dose-dependent manner

l-DOPA induced extracellular dopamine (DA), norepinephrine (NE) and serotonin (5-HT) in the ventromedial hypothalamus (VMH) of chickens were measured by in vivo microdialysis. Several doses of 3,4-dihydroxy-l-phenylalanine (l-DOPA) were administered locally through the microdialysis probe into the VMH of chickens for 10 min. Local perfusion of l-DOPA increased the extracellular levels of DA. The increased DA was dose-related and was significantly higher compared to the baseline and control group. The maximal level of DA was 212% and 254%, respectively, of the baseline following administration of 1 and 2 μg/ml l-DOPA. There were no changes in NE and 5-HT levels from baseline after l-DOPA perfusion. l-DOPA (1 μg/ml) was mixed with Ca²⁺-free Ringer, tetrodotoxin (TTX) (2 μM) and high K⁺ and was perfused for 30 min into the chicken VMH. TTX and Ca²⁺-free Ringer's solution inhibited the effectiveness of l-DOPA in increasing DA release. The NE and 5-HT levels were significantly lower than the baseline. After administration of K⁺ a significant increase of DA, NE and 5-HT was observed. The microdialysis results are consistent with our objective that l-DOPA induced extracellular DA increases in the VMH in a dose-dependent manner and the released DA, NE and 5-HT within the dialysate were related to neuronal activity.     

Neuronal Nitric Oxide Synthase Activation Is Involved in Insulin-Mediated Cardiovascular Effects in the Nucleus Tractus Solitarii of Rats

Neuronal nitric oxide synthases (nNOS) is distributed throughout the central nervous system (CNS) and has been proposed to modulate neuronal activity in the nucleus tractus solitarii (NTS). Here, we investigated whether the activation of nNOS is involved in insulin-induced cardiovascular responses in the NTS. Insulin (100 IU/ml) was unilaterally microinjected into the NTS, and the cardiovascular effects were evaluated before and after microinjection of the nNOS inhibitors 7-nitroindazole (7-NI) (5 pmol) and N(5)-(1-imino-3-butenyl)-l-ornithine (vinyl-L-NIO) (600 pmol). Western blot and immunohistochemical analyses were performed to determine nNOS phosphorylation levels after insulin or phosphoinositide 3-kinase (PI3K) inhibitor LY294002 microinjection into the NTS. Unilateral microinjection of insulin into the NTS produced prominent depressor and bradycardic effects in WKY rats. Pretreatment with the nNOS inhibitors 7-NI and Vinyl-L-NIO attenuated the cardiovascular response evoked by insulin in Wistar-Kyoto (WKY) rats. Moreover, Western blot analysis showed a significant increase in nNOS (16.5±0.4-fold; P<0.05; n=4) phosphorylation after insulin injection, whereas the PI3K inhibitor LY294002 abolished the insulin-induced effects. In situ nNOS phosphorylation was found to be increased in the NTS after insulin injection. Furthermore, co-immunoprecipitation assay showed Akt and nNOS can bind to each other as detected by phospho-Akt^S473 and phospho-nNOS^S1416 antibodies. In vitro kinase assay showed insulin activated Akt can directly phosphorylate nNOS^S1416. These results demonstrated that nNOS may couple with the activation of the insulin receptor, via the liberation of NO, in order to participate in central cardiovascular regulation of WKY rats.     

The evidence for tonic GABAergic regulation of basal L-DOPA release via activation of inhibitory GABA(A) receptors in the nucleus tractus solitarii of anesthetized rats

We have proposed that DOPA is a neurotransmitter of the primary baroreceptor afferents terminating in the rat nucleus tractus solitarii (NTS). GABA is a putative inhibitory neuromodulator for baroreflex inputs in the NTS. Thus, GABA may inhibit DOPAergic transmission in the NTS. We tried to clarify whether basal DOPA release is inhibited by muscimol, a GABA(A) agonist, and facilitated by bicuculline, a GABA(A) antagonist, during microdialysis of the NTS in anesthetized rats. DOPA release was consistently detectable. Muscimol 10-100 microM perfused via probes gradually inhibited concentration-dependently DOPA release. Peak 30% inhibition occurred 2 h after perfusion. Muscimol (30 microM)-induced inhibition was antagonized by non-effective 10 microM bicuculline. Bicuculline (30 microM) elicited peak 30% facilitation of DOPA release 2 h after perfusion. Endogenous GABA seems to regulate tonically basal DOPA release via activation of inhibitory GABA(A) receptors in the rat NTS. These findings further support the above proposal.     

Mechanism of induction of immunological tolerance: V. Priming and tolerance with small doses of polymerized flagellin*

The particulate antigen, polymerized flagellin, was shown to be effective both in immunological priming and in inducing tolerance in newborn Wistar rats. The following results were obtained:

(1) A single injection of 100 ng or more at birth caused priming without a primary response. A secondary response could be elicited 7 or more days after birth with a dose of 10–100 μg.

(2) Daily injections of 100 ng to 1 μg/g body weight of polymerized flagellin during the first 2 weeks of life abrogated the priming effect and in fact gave rise to a state of high dosage-zone immunological tolerance.

(3) The injection of 1 μg to 10^-5 pg/g body weight/day into newborn rats for 2 weeks gave rise to two zones of tolerance separated by a slight `immunity hump', which suggested the presence of some primed cells but fewer virgin cells following these intermediate doses.

(4) The low zone of tolerance was induced by a dose of 10^-4 pg/g body weight/day, which was equivalent to an initial antigen concentration in the animal of about 10^-20 M, if one adopts the simplified assumption that polymerized flagellin has a molecular weight of 10 × 10⁶. High zone tolerance was induced by doses of 100 ng/g body weight/day or more and the immunity region by 1 ng/body weight/day.

(5) In the low zone, polymerized flagellin appears to induce tolerance even better in newborn rats than the lower molecular-weight monomeric flagellin. The extremely small amounts which are effective are difficult to explain, but raise the possibility of some antigen concentrating mechanism.

     

l-DOPA treatment reverses the motor alterations induced by manganese exposure as a Parkinson disease experimental model

This investigation was designed to determine whether l-DOPA treatment improves the motor alterations observed after divalent and trivalent manganese (Mn) mixture inhalation on mice to ensure that the alterations are of dopaminergic origin. CD-1 male mice inhaled a mixture of 0.04 M manganese chloride (MnCl₂) and manganese acetate (Mn(OAc)₃), 1 h twice a week for 5 months. Before Mn exposure, animals were trained to perform motor function tests and were evaluated each week after the exposure. Overall behavior was assessed by ratings and by videotaped analyses; by the end of Mn exposure period, 10 mice were orally treated with 7.5 mg/kg l-DOPA. After 5 months of Mn-mixture inhalation striatal dopamine content decreased 71%, mice developed evident deficits in motor performance manifested as akinesia, postural instability and action tremor; these alterations were reverted with l-DOPA treatment. Our results suggest that the motor alterations induced by the inhalation of the combination of MnCl₂/Mn(OAc)₃ are related to nigrostriatal dopaminergic function providing new light on the understanding of manganese neurotoxicity as a suitable Parkinson disease experimental model.     

Nitric oxide synthase inhibition attenuates l-DOPA-induced dyskinesias in a rodent model of Parkinson's disease

Chronic l-DOPA pharmacotherapy in Parkinson's disease is often accompanied by the development of abnormal and excessive movements known as l-DOPA-induced dyskinesia. Rats with 6-hydroxydopamine lesion of dopaminergic neurons chronically treated with l-DOPA develop a rodent analog of this dyskinesia characterized by severe axial, limb, locomotor and orofacial abnormal involuntary movements. While the mechanisms by which these effects occur are not clear, they may involve the nitric oxide system. In the present study we investigate if nitric oxide synthase inhibitors can prevent dyskinesias induced by repeated administration of l-DOPA in rats with unilateral 6-hydroxydopamine lesion. Chronic l-DOPA (high fixed dose, 100 mg/kg; low escalating dose, 10–30 mg/kg) treatment induced progressive dyskinesia changes. Two nitric oxide synthase inhibitors, 7-nitroindazole (1–30 mg/kg) and NG-nitro-l-arginine (50 mg/kg), given 30 min before l-DOPA, attenuate dyskinesia. 7-Nitroindazolee also improved motor performance of these animals in the rota-rod test. These results suggest the possibility that nitric oxide synthase inhibitors may be useful to treat l-DOPA-induced dyskinesia.     

Involvement of nitric oxide production via kynurenic acid-sensitive glutamate receptors in DOPA-induced depressor responses in the nucleus tractus solitarii of anesthetized rats

We have proposed the hypothesis that L-3,4-dihydroxyphenylalanine (DOPA) plays a role of neurotransmitter of the primary baroreceptor afferents terminating in the nucleus tractus solitarii (NTS). In the present study, we tried to clarify whether glutamate receptors and/or nitric oxide (NO), important modulators for central cardiovascular regulation, are involved in the DOPA-induced cardiovascular responses in the nucleus. Male Wistar rats were anesthetized with urethane and artificially ventilated. Compounds or antisense oligos (17-mer) for neuronal NO synthase were microinjected into depressor sites of the unilateral nucleus. DOPA 30-300 pmol microinjected into the nucleus dose-dependently induced depressor and bradycardic responses. Prior injection of kynurenic acid (600 pmol) suppressed DOPA (300 pmol)-induced responses by approximately 80%. Prior injection of N(G)-monomethyl-L-arginine 100 nmol, a potent NO synthase inhibitor, reversibly attenuated by approximately 90% DOPA-induced responses, while the D-isomer 100 nmol produced no effect. Furthermore, prior injection of neuronal NO synthase antisense oligos (20 pmol) reversibly reduced by approximately 70% responses to DOPA. Sense or scrambled oligos produced no effect. A NO precursor L-arginine (30 nmol) induced depressor and bradycardic responses, but these responses were not affected by kynurenic acid. These results suggest important roles for glutamate receptors and NO in DOPA induced-depressor and bradycardic responses in the NTS.     

Effects of the administration of a catalase inhibitor into the fourth cerebral ventricle on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke

OBJECTIVE:

Previous studies have demonstrated a relationship between brain oxidative stress and cardiovascular regulation. We evaluated the effects of central catalase inhibition on cardiovascular responses in spontaneously hypertensive rats exposed to sidestream cigarette smoke.

METHODS:

Male Wistar Kyoto (WKY) rats and spontaneously hypertensive rats (SH) (16 weeks old) were implanted with a stainless steel guide cannula leading into the fourth cerebral ventricle (4^th V). The femoral artery and vein were cannulated for arterial pressure and heart rate measurement and drug infusion, respectively. The rats were exposed to sidestream cigarette smoke for 180 minutes/day, 5 days/week for 3 weeks (CO: 100-300 ppm). The baroreflex was tested using a pressor dose of phenylephrine (8 μg/kg, bolus) and a depressor dose of sodium nitroprusside (50 μg/kg, bolus). Cardiovascular responses were evaluated before and 5, 15, 30 and 60 minutes after injection of a catalase inhibitor (3-amino-1,2,4-triazole, 0.001 g/100 μL) into the 4^th V.

RESULTS:

Vehicle administration into the 4^th V did not affect the cardiovascular response, whereas administration of the central catalase inhibitor increased the basal HR and attenuated the bradycardic peak (p<0.05) to a greater extent in WKY rats exposed to sidestream cigarette smoke than in WKY rats exposed to fresh air. However, in spontaneously hypertensive rats, the effect of the catalase inhibitor treatment was stronger in the fresh air condition (p<0.05).

CONCLUSION:

Administration of a catalase inhibitor into the 4^th V combined with exposure to sidestream cigarette smoke has a stronger effect in WKY rats than in SH rats.     

Inhalation challenge testing of latex-sensitive health care workers and the effectiveness of laminar flow HEPA–filtered helmets in reducing rhinoconjunctival and asthmatic reactions

Background: There are few data relating latex aeroallergen concentrations to biologic responses in latex-sensitized persons. Objectives: We sought to investigate acceptable latex aeroallergen concentrations below which latex-sensitive health care workers do not experience symptoms and to study the effect of high-efficiency particle arrest (HEPA)–filtered laminar flow helmets in preventing latex-induced symptoms. Methods: Under challenge chamber conditions, latex-sensitive health care workers underwent 7 sequential inhalation challenge tests by donning and discarding either vinyl gloves (challenge 1), low latex–allergen powder-free gloves (challenge 2), or high latex–allergen powdered gloves (challenges 3 to 7) for up to 1 hour. Volunteers wore a laminar flow helmet during all challenges; HEPA filters in the helmet were in place only during challenges 3 and 4. Flow-volume loops, symptom scores, and latex aeroallergen concentrations were measured before and during each test. Results: At 60 minutes, latex aeroallergen concentrations during challenges 3 to 7 (mean, 7600 ng/m³ ; range, 93 to 54,000 ng/m³ ) were significantly higher than during challenges 1 or 2 (mean, 65 ng/m³ ; range, nondetectable to 100 ng/m³ ) (P < .001). During challenges 5 and 6, mean maximum percent falls in FEV₁ (–16% and –11%, respectively) were significantly greater compared with those measured during challenges 3 and 4 (–3% and –1%, respectively) (P = .03). Mean maximum change from baseline symptom scores during challenges 5 and 6 was significantly higher than that during challenges 3 and 4 (P = .006). During challenges with high latex–allergen gloves, 4 volunteers had reproducible FEV₁ falls of 20% or greater at cumulative inhaled latex aeroallergen doses ranging from less than 100 ng to 1500 ng. Conclusion: The laminar flow helmets were effective in reducing latex-induced symptoms. Only 1 volunteer exhibited a fall in FEV₁ of 20% or greater after a cumulative inhaled latex aeroallergen dose of less than 100 ng, and no volunteer showed a decline in FEV₁ after exposure to powder-free low allergen gloves. (J Allergy Clin Immunol 1998;102:998-1004.)     

Influence of opioids and naloxone on rhythmic motor activity in spinal cats

The effects of l-DOPA, naloxone, and the opioids (d-Ala²,N-Me-Phe⁴,Gly⁵-ol)-enkephalin (DAGO) and d-Ser²-Leu-enkephalin-Thr⁶ (DSLET) on spinal motor rhythm generation were compared in anemically decapitated high spinal cats. After premedication with nialamide, DOPA caused the well-known, slow rhythmic motor activity with a locomotor pattern. The cycle duration of the evoked rhythm was usually between 3.9 and 5.0 s. The opioids DAGO and DSLET, injected intravenously (1.2–2 mg/kg) or suffused over the lumbar spinal cord (10^-3–10^-4 M in Ringer's solution), severely depressed the DOPA-induced rhythmic activity, sometimes completely abolishing efferent motor activity. Naloxone (0.5–1 mg/kg i.v.) exerted different rhythm-facilitating effects, depending on the experimental condition. In the acute phase after spinalization, without paralysis and without nialamide and DOPA, naloxone induced rhythmic movements with a main frequency of 1.2–2 Hz. In the same preparation with paralysis, naloxone induced a rhythmic motor activity with a distinctly higher frequency (main range 4.3–5.8 Hz). After premedication with nialamide and DOPA, naloxone facilitated or, if a rhythm was absent, induced the slow-frequency DOPA type of rhythm. Given after i.v. or topical opioid application, naloxone antagonized the rhythm-depressing action of the opioid and caused an additional facilitation of rhythmic activity. Dopa and naloxone facilitated the long-latency, segmental reflex pathways from flexor reflex afferents (FRA), while the opioids depressed them. The short-latency FRA pathways were depressed by DOPA and opioids but were facilitated by naloxone.The influence of the different drugs on spinal motor rhythm generation is discussed in relation to their influence on short- and long-latency segmental pathways from FRA. If the rhythm generation induced by DOPA is based on the release of the long-latency FRA pathways, as has been proposed before, the rhythm-depressing action of opioids may be due to the suppression of these pathways, and the particular rhythm-generating function of naloxone may be related to its facilitation of short- and long-latency FRA pathways.     

The interaction between short-term exercise training and a diuretic-induced hypovolemic stimulus

Nine healthy untrained males [mean (SEM) age, 20.2 (1) years; peak oxygen uptake (VO_2max, 48.2 (2) ml · kg^–1 · min^–1] took part in a study to examine whether short-term exercise training (cycle exercise 2 h · day^–1 for 3 days at 60% ), which normally results in an expansion of plasma volume (PV), can counteract a diuretic-induced hypovolemic stimulus (100 mg triamterene + 50 mg hydrochlorothiazide day^–1 for 5 days concurrent with exercise training) and restore PV to control levels. Resting and exercise responses (90 min, 60% ) in the diuretic plus exercise training condition (D + E) were compared to a control (C) and a diuretic (D) condition in which no exercise was performed. Following the short-term training, PV was still decreased (P < 0.05) below C by –8.3 (3)% in D + E and was similar (P > 0.05) to the reduction in D [–12.4 (2)%]. The reduced PV in response to the diuretic was associated with similar (P > 0.05) elevations in resting aldosterone (ALDO) and norepinephrine (NOREPI) levels (ng · 100 ml^–1) in D [101 (12), 61 (4)] and D + E [85 (16), 60 (10)] above (P < 0.05) C [22 (5), 37 (4)]. During exercise, ALDO levels were increased (P < 0.05) by 66 (5) and 70 (10) ng · 100 ml^–1 in D and D + E, respectively, and the increase was greater (P < 0.05) than C [44 (8) ng · 100 ml^–1]. The rise in NOREPI during exercise was lower (P < 0.05) in D + E [164 (44) ng · 100 ml^–1] than in D [244 (24) ng · 100 ml^–1] with levels similar to C [176 (25) ng · 100 ml^–1]. Thus, the ALDO response to the diuretic was heightened at rest and during exercise but was not additionally affected by the short-term training session. Results suggest that 3 days of exercise training are unable to counteract the hypovolemic effects of a diuretic and restore PV to control levels despite chronic elevations in NOREPI and ALDO.     

Participation of the NO/cGMP/K+ATP pathway in the antinociception induced by Walker tumor bearing in rats

Implantation of Walker 256 tumor decreases acute systemic inflammation in rats. Inflammatory hyperalgesia is one of the most important events of acute inflammation. The L-arginine/NO/cGMP/K⁺ATP pathway has been proposed as the mechanism of peripheral antinociception mediated by several drugs and physical exercise. The objective of this study was to investigate a possible involvement of the NO/cGMP/K⁺ATP pathway in antinociception induced in Walker 256 tumor-bearing male Wistar rats (180-220 g). The groups consisted of 5-6 animals. Mechanical inflammatory hypernociception was evaluated using an electronic version of the von Frey test. Walker tumor (4th and 7th day post-implantation) reduced prostaglandin E₂- (PGE₂, 400 ng/paw; 50 µL; intraplantar injection) and carrageenan-induced hypernociception (500 µg/paw; 100 µL; intraplantar injection). Walker tumor-induced analgesia was reversed (99.3% for carrageenan and 77.2% for PGE₂) by a selective inhibitor of nitric oxide synthase (L-NAME; 90 mg/kg, ip) and L-arginine (200 mg/kg, ip), which prevented (80% for carrageenan and 65% for PGE₂) the effect of L-NAME. Treatment with the soluble guanylyl cyclase inhibitor ODQ (100% for carrageenan and 95% for PGE₂; 8 µg/paw) and the ATP-sensitive K⁺ channel (KATP) blocker glibenclamide (87.5% for carrageenan and 100% for PGE₂; 160 µg/paw) reversed the antinociceptive effect of tumor bearing in a statistically significant manner (P < 0.05). The present study confirmed an intrinsic peripheral antinociceptive effect of Walker tumor bearing in rats. This antinociceptive effect seemed to be mediated by activation of the NO/cGMP pathway followed by the opening of KATP channels.     

Intravenously injected radiolabelled fatty acids image brain tumour phospholipids in vivo: differential uptakes of palmitate,arachidonate and docosahexaenoate

This paper investigates the incorporation of intravenously (i.v.) administered radiolabelled fatty acids—[9, 10-³H]palmitate (³H-PA), [1-¹⁴C]arachidonate (¹⁴C-AA) and [1-¹⁴C]docosahexaenoate (¹⁴C-DHA)—into intracerebrally implanted tumours in awake Fischer-344 rats. A suspension of Walker 256 carcinosarcoma tumour cells (1 × 106 cells) was implanted into the right cerebral hemisphere of 8- to 9-week-old rats. Seven days after implantation, the awake rat was infused i.v. for 5 min with ³H-PA (6.4 mCi/kg), ¹⁴C-AA (170 µCi/kg) or ¹⁴C-DHA (100 µCi/kg). Twenty minutes after the start of infusion, the rat was killed and coronal brain sections were obtained for quantitative autoradiography and histology. Each fatty acid showed well-demarcated incorporation into tumour tissue. Areas of necrosis or haemorrhage showed no or small levels of incorporation. The ratios of incorporation into the tumour to incorporation into contralateral brain regions were 2.8–5.5 for ³H-PA, 2.1–3.3 for ¹⁴C-AA and 1.5–2.2 for ¹⁴C-DHA. The mean ratios differed significantly between the fatty acids (p < 0.01). ³H-PA was not incorporated into necrotic tumours despite the presence of an open blood-tumour barrier, indicated by extravasated horseradish peroxidase. The incorporation rate constant of ³H-PA was similar for small intracerebral and large extracerebral tumours. The results show that ³H-PA, ¹⁴C-AA and ¹⁴C-DHA. are incorporated more readily into tumour tissue than into brain, and that the increase is primarily due to increased utilization of fatty acids by tumour cells and not due to a high blood-tumour permeability. The relative increases in rates of incorporation for the different fatty acids may be related to lipid composition of the tumour and to the requirement of and specific role of these fatty acids in tumour cell growth and division.     

Cerebral blood flow decreases following microinjection of sodium nitroprusside into the nucleus tractus solitarii of anesthetized rats

The present study was undertaken to examine the effects of microinjection of sodium nitroprusside (SNP), which releases nitric oxide (NO) spontaneously, into the nucleus tractus solitarii (NTS) on cerebral circulation. Cerebral blood flow (CBF) was measured in urethane-anesthetized (1.5 g·kg^?1, i.p.), paralysed and artificially ventilated rats using labeled microspheres or laser Doppler flowmetry. The CBF was significantly decreased by microinjection of SNP (5 nmol, n=10, microsphere technique; 0.5 nmol, n=6, laser Doppler flowmetry) into the unilateral NTS. Microinjection of N ^G-monomethyl-L-arginine (L-NMMA), an inhibitor of the formation of NO, prevented cerebral vasoconstrictor responses induced by microinjection of l-glutamate into the NTS (n=10). Microinjection of N ^G-monomethyl-d-arginine (D-NMMA) had no effect on the cerebral vasoconstrictor responses induced by l-glutamate (n=11). Unilateral microinjections of L-NMMA into the NTS (n=9), of SNP into the area adjacent to the NTS (n=9), of vehicle solution into the NTS (n=10), and of light-inactivated SNP into the NTS (n=6) had no effect on cerebral circulation. Cerebral autoregulation was well maintained in our protocols (n=9). These results indicate that microinjection of SNP, an NO donor, into the NTS decreases CBF.     

CO2 decreases membrane conductance and depolarizes neurons in the nucleus tractus solitarii

Summary To identify central sites of potential CO₂/H⁺-chemoreceptive neurons, and the mechanism responsible for neuronal chemosensitivity, intracellular recordings were made in rat tissue slices in two cardiopulmonary-related regions (i.e., nucleus tractus solitarii, NTS; nucleus ambiguus, AMBc) during exposure to high CO₂. When the NTS was explored slices were bisected and the ventral half discarded. Utilizing such dorsal medullary slices removed any impinging synaptic input from putative chemoreceptors in the ventrolateral medulla. In the NTS, CO₂-induced changes in firing rate were associated with membrane depolarizations ranging from 2–25 mV (n = 15). In some cases increased e.p.s.p. activity was observed during CO₂ exposure. The CO₂-induced depolarization occurred concomitantly with an increased input resistance ranging from 19–23 M (n = 5). The lower membrane conductance during hypercapnia suggests that CO₂-induced depolarization is due to a decreased outward potassium conductance. Unlike neurons in the NTS, AMBc neurons were not spontaneously active and were rarely depolarized by hypercapnia. Eleven of 12 cells tested were either hyperpolarized by or insensitive to CO₂. Only 1 neuron in the AMBc was depolarized and it also showed an increased input resistance during CO₂ exposure. Our findings suggest that CO₂/H⁺-related stimuli decrease potassium conductance which depolarizes the cell and increases firing rate. Although our in vitro studies cannot guarantee the specific function of these cells, we believe they may be involved with brain pH homeostasis and cardiopulmonary regulation.     

Superoxide generation by alveolar macrophages from aged rats: improvement by in vitro treatment with IFN-γ

Alveolar macrophages (AM) from aged rats show an impaired oxidative response, but it is unclear whether or not this is due to the inability of these cells to be activated. To elucidate this, we investigated the capacity of AM from young (16-week-old) and aged (100-week-old) rats to become primed with recombinant rat interferon-γ (IFN-γ) for increased phorbol myristate acetate (PMA)-elicited O₂⁻ production, utilizing an MCLA-dependent chemiluminescent assay. We also compared concanavalin A- or Bacillus Calmette Guerin (BCG)-induced IFN-γ production by the spleen cells of young and aged animals. The data indicated that AM freshly harvested from non-sensitized aged rats produced less O₂⁻ than those from young animals. A similar result was obtained in BCG-sensitized rats. However, AM from aged rats were primed with in vitro treatment with IFN-γ for increased rate of O₂⁻ production to an equivalent level of that by AM from young animals. In addition, the ability of spleen cells to produce IFN-γ was well maintained in aged rats. These results suggest that AM function is suppressed in the lungs of aged animals. Our observation that the decreased AM function in aged rats can be reversed is important because it suggests that appropriate treatment may reduce the incidence and mortality of respiratory infections in the elderly.     

Immunoreactive β-endorphin in the plasma, pituitary and hypothalamus of young and old male rats

Immunoreactive beta-endorphin (IR-β-ENDO) was measured in the plasma, pituitary, and hypothalamus of young (3–5 mo.) and old (19–23 mo.) male Sprague-Dawley rats, using a specific radioimmunoassay. Plasma IR-β-ENDO in old male rats (3.44±10.54 ng/ml) was more than three times higher than values observed in young male rats (1.00±0.10 ng/ml). Pituitary content and concentration of IR-β-ENDO also were significantly greater in the old (5.85±0.51 μg/gland and 1.17±0.10 μg/mg protein) than in the young (3.53±0.29 μg/gland and 0.78±0.06 μg/mg protein) male rats. The content of IR-β-ENDO in the hypothalamus of old and young rats was nearly the same (43.45±2.47 and 49.88±6.35 ng/hypothalamus, respectively), whereas the concentration of IR-β-ENDO in the hypothalamus of the old male rats (3.89±0.25 ng/mg protein) was approximately 50% lower than that observed in the young male rats (7.80±0.85 ng/mg protein). These changes in plasma, pituitary, and hypothalamic IR-β-ENDO may contribute to the increase in prolactin and decrease in gonadotropins observed in old male rats, since β-ENDO administration is known to produce these effects on prolactin and gonadotropin secretion.     

A study on the short-term effect of cafeteria diet and pioglitazone on insulin resistance and serum levels of adiponectin and ghrelin

The interaction between ghrelin and adiponectin is still controversial. We investigated the effect of cafeteria diet and pioglitazone on body weight, insulin resistance, and adiponectin/ghrelin levels in an experimental study on male Wistar rats. The animals were divided into four groups of 6 rats each, and received balanced chow with saline (CHOW-O) or pioglitazone (CHOW-P), or a cafeteria diet with saline (CAFE-O) or pioglitazone (CAFE-P). The chow/cafeteria diets were administered for 35 days, and saline/pioglitazone (10 mg·kg body weight⁻¹·day⁻¹) was added in the last 14 days prior to euthanasia. CAFE-O animals had a higher mean final weight (372.5 ± 21.01 g) than CHOW-O (317.66 ± 25.11 g, P = 0.017) and CHOW-P (322.66 ± 28.42 g, P = 0.035) animals. Serum adiponectin levels were significantly higher in CHOW-P (55.91 ± 20.62 ng/mL) than in CHOW-O (30.52 ± 6.97 ng/mL, P = 0.014) and CAFE-O (32.54 ± 9.03 ng/mL, P = 0.027) but not in CAFE-P. Higher total serum ghrelin levels were observed in CAFE-P compared to CHOW-P animals (1.65 ± 0.69 vs 0.65 ± 0.36 ng/mL, P = 0.006). Likewise, acylated ghrelin levels were higher in CAFE-P (471.52 ± 195.09 pg/mL) than in CHOW-P (193.01 ± 87.61 pg/mL, P = 0.009) and CAFE-O (259.44 ± 86.36 pg/mL, P = 0.047) animals. In conclusion, a cafeteria diet can lead to a significant weight gain. Although CAFE-P animals exhibited higher ghrelin levels, this was probably related to food deprivation rather than to a direct pharmacological effect, possibly attenuating the increase in adiponectin levels.