KCN Injection Research Articles

Changes in the autonomic and respiratory patterns of mice submitted to short‐term sustained hypoxia

Short-term sustained hypoxia (SH) in rats induces changes in sympathetic-respiratory coupling and sympathetic overactivity, which seems to be linked to hypertension. However, there is no previous experimental data about the effects of SH on the autonomic and respiratory pattern in mice. In the present study we tested the hypothesis that mice submitted to SH present autonomic and respiratory changes similarly to rats. To reach this goal we evaluated the effects of 24-hour SH exposure on cardiovascular, respiratory and autonomic parameters in baseline conditions and upon chemoreflex activation.C57BL/6J mice (7-8 weeks old, ~25g) were deeply anesthetized for femoral artery and jugular vein catheterization. Four days later, they were submitted to SH (24h, FiO2 0.1) or normoxia. At the end of SH protocol, arterial pressure, heart rate and ventilation were recorded in vivo. Peripheral chemoreflex was activated via KCN injection (0.16 mg/Kg, i.v.). In another experimental group, we performed in situ recordings of phrenic (PN), abdominal, (AbN), cervical vagus (cVN) and thoracic sympathetic (tSN) nerves activities of SH mice using the working heart-brainstem preparation. All experimental protocols were approved by the Institutional Ethics Committee (#140/2019 and #163/2019). In the in vivo approach, although SH mice (n=13) presented a significant decrease in baseline HR (510 ± 22 vs 633 ± 16 beats min-1; P = 0.002) compared with the controls (n=17), no differences were observed in mean arterial pressure levels (109 ± 2 vs 106 ± 2 mmHg; P=0.443). SH mice (n=14) also showed significantly increased respiratory frequency [(fR) 277 ± 8 vs 203 ± 6 breaths.min-1; P <0.0001], tidal volume [(VT) 14 ± 1 vs. 12 ± 1mL.Kg1; P = 0.0019)], and ventilation [(VE) 3927 ± 164 vs 2390 ± 104 mL.Kg-1.min-1; P < 0.0001)] compared with controls (n=17). The magnitudes of bradycardic responses to chemoreflex activation were greater in SH mice (n=8) than in controls (n=11; -329 ± 36 vs -210 ± 30 beats min-1, P=0.02). In the in situ approach, baseline PN discharge (PND) frequency was significantly reduced in SH mice (n=11) in relation to controls (n=26) (0.69 ± 0.06 vs 1.13 ± 0.10 Hz, P=0.0154). The incidence of Late-E bursts in AbN activity in SH mice (n=10) was significantly increased in relation to controls (n=20) (83.3 ± 7.7 vs 24.3 ± 8.0%, P<0.0001). The duration of expiration in SH mice (n=11) was longer than in controls (n=22) (1.13 ± 0.16 vs 0.67 ± 0.07s, P= 0.0002) due to an increase in the duration of post-inspiration (0.78 ± 0.12 vs 0.35 ± 0.04s, P= 0.0032). tSNA in the SH group (n=10) was significantly reduced during late-expiration (E2) compared with the control group (n=16) (19.0 ± 4.3 vs 39.7 ± 4.2%, P= 0.0203). The data are showing that 24-h SH protocol in mice produces: a) an increase in parasympathetic tone to the heart, which seems to be related to changes in their breathing pattern; and b) prolonged expiration and active expiration associated with a reduction in sympathetic activity during E2. This autonomic imbalance favoring the parasympathetic componente may explain why mice, different of rats, do not develop hypertension after SH.

Cyanide Poisoning Compromises Gene Pathways Modulating Cardiac Injury in Vivo.

Smoke inhalation from a structure fire is a common route of cyanide poisoning in the U.S. Cyanide inhibits cellular respiration, often leading to death. Its rapid distribution throughout the body can result in injuries to multiple organs, and cyanide victims were reported to experience myocardial infarction and other cardiac complications. However, molecular mechanisms of such complications are yet to be elucidated. While FDA-approved CN antidotes such as sodium thiosulfate and hydroxocobalamin are clinically used, they have foreseeable limitations during mass casualty situations because they require intravenous administration. To facilitate the development of better antidotes and therapeutic treatments, a global view of molecular changes induced by cyanide exposure is necessary. As an exploratory pursuit, we performed oligonucleotide microarrays to establish cardiac transcriptomes of an animal model of nose-only inhalation exposure to hydrogen cyanide (HCN), which is relevant to smoke inhalation. We also profiled cardiac transcriptomes after subcutaneous injection of potassium cyanide (KCN). Although the KCN injection model has often been used to evaluate medical countermeasures, this study demonstrated that cardiac transcriptomes are largely different from that of the HCN inhalation model at multiple time points within 24 h after exposure. Pathway analysis identified that HCN-induced transcriptomes were enriched with genes encoding mediators of pathways critical in modulation of cardiac complications and that a large number of such genes were significantly decreased in expression. We utilized the upstream regulatory analysis to propose drugs that can be potentially employed to treat cyanide-induced cardiac complications.

Activation of the carotid body increases directly recorded cardiac sympathetic nerve activity and coronary blood flow in conscious sheep.

Activation of the carotid body (CB) using intracarotid potassium cyanide (KCN) injection increases coronary blood flow (CoBF). This increase in CoBF is considered to be mediated by co-activation of both the sympathetic and parasympathetic nerves to the heart. However, whether cardiac sympathetic nerve activity (cardiac SNA) actually increases during CB activation has not been determined previously. We hypothesized that activation of the CB would increase directly recorded cardiac SNA, which would cause coronary vasodilatation. Experiments were conducted in conscious sheep implanted with electrodes to record cardiac SNA and diaphragmatic electromyography (dEMG), flow probes to record CoBF and cardiac output, and a catheter to record arterial pressure. Intracarotid KCN injection was used to activate the CB. To eliminate the contribution of metabolic demand on coronary flow, the heart was paced at a constant rate during CB chemoreflex stimulation. Intracarotid KCN injection resulted in a significant increase in directly recorded cardiac SNA frequency (from 24 ± 2 to 40 ± 4 bursts/min; P < 0.05) as well as a dose-dependent increase in mean arterial pressure (79 ± 15 to 88 ± 14 mmHg; P < 0.01) and CoBF (75 ± 37 vs. 86 ± 42 mL/min; P < 0.05). The increase in CoBF and coronary vascular conductance to intracarotid KCN injection was abolished after propranolol infusion, suggesting that the increased cardiac SNA mediates coronary vasodilatation. The pressor response to activation of the CB was abolished by pretreatment with intravenous atropine, but there was no change in the coronary flow response. Our results indicate that CB activation increases directly recorded cardiac SNA, which mediates vasodilatation of the coronary vasculature.

Roles of glutamate and GABA of the Kölliker-Fuse nucleus in generating the cardiovascular chemoreflex.

The Kölliker-Fuse (KF) nucleus is a part of the parabrachial complex, located in the dorsolateral pons. It is involved in the chemoreflex-evoked cardiovascular and respiratory changes, but the role of GABA and glutamate in cardiovascular chemoreflex has not been shown yet. This study was performed to determine the role of GABA, glutamate, and their interaction in the KF, in cardiovascular chemoreflex in anesthetized rat. The antagonists were microinjected into the KF, and arterial pressure, heart rate, and single-unit responses were recorded simultaneously. The chemoreflex was evoked by i.v. injection of KCN, consisted of a short pressor followed by long bradycardia responses. Both responses were significantly attenuated by injection of a synaptic blocker (CoCl2) into the KF, confirming involvement of the KF in generating the reflex. Microinjection of AP5, an NMDA receptor antagonist, into the KF significantly attenuated the pressor and bradycardia responses, while blocking the AMPA receptors by CNQX had no significant effect. Blockade of GABAA receptors by bicuculline methiodide (BMI) potentiated both responses. Co-injection of BMI and CNQX potentiated the responses too. Co-injection of BMI and AP5 had no significant effect on the pressor response but significantly attenuated the bradycardia response. In conclusion, the KF plays a role in generating cardiovascular chemoreflex via its glutamate NMDA but not AMPA receptors. GABA inhibits both components of this reflex through GABAA receptors. There is an interaction between GABAA and NMDA receptors in regulating the bradycardia response of the reflex. Single-unit results were also presented which were correlated with and supported the homodynamic findings.

DMTS is an effective treatment in both inhalation and injection models for cyanide poisoning using unanesthetized mice

Context: Cyanide (CN) is a metabolic poison, halting ATP synthesis by inhibiting complex IV of the electron transport chain. If exposed at high enough concentrations, humans and most animals can die within minutes. Because time is a crucial factor in survival of CN poisoning, a rapidly bioavailable, nontoxic, easy to administer CN medical countermeasure could improve morbidity/mortality in a mass CN exposure scenario. The most likely route of exposure to CN is via inhalation.Objective: This study examined the efficacy of a new formulation for dimethyl trisulfide (DMTS), a countermeasure which has shown promise as a treatment for CN poisoning, using both inhalation and injection models of CN exposure.Methods: We developed a model of acute CN inhalation intoxication, using the highly toxic agent system from CH Technologies for nose-only exposure. Both continuous and discontinuous HCN exposure paradigms were implemented. For comparison, we also utilized a potassium cyanide (KCN) injection model. In all experiments, DMTS was administered as a cyanide countermeasure via intramuscular injection in unanesthetized mice.Results: We found DMTS administration to be highly protective against both subcutaneous KCN and HCN inhalation toxicity. In the KCN injection model, DMTS afforded protection against 3.73 times the LD50 dose of KCN. In our HCN inhalation exposure model, mice challenged with LC50 HCN doses for the duration of either 10- or 40-minute exposure paradigms demonstrated improved survival in the presence of DMTS treatment (87.5% and 90.0% survival, respectively). Animals in the DMTS treatment groups of both lethal exposure models similarly exhibited improvement in observed toxic signs.Conclusion: We show that a newly developed formulation of DMTS is efficacious within two lethal CN exposure mouse models (inhalation and injection) and is highly effective by intramuscular injection. Within these HCN studies, we demonstrate efficacy of DMTS in both continuous and discontinuous inhalation exposure models.

On the verge of a respiratory-type panic attack: Selective activations of rostrolateral and caudoventrolateral periaqueductal gray matter following short-lasting escape to a low dose of potassium cyanide

Intravenous injections of potassium cyanide (KCN) both elicit escape by its own and facilitate escape to electrical stimulation of the periaqueductal gray matter (PAG). Moreover, whereas the KCN-evoked escape is potentiated by CO2, it is suppressed by both lesions of PAG and clinically effective treatments with panicolytics. These and other data suggest that the PAG harbors a hypoxia-sensitive alarm system the activation of which could both precipitate panic and render the subject hypersensitive to CO2. Although prior c-Fos immunohistochemistry studies reported widespread activations of PAG following KCN injections, the employment of repeated injections of high doses of KCN (>60µg) in anesthetized rats compromised both the localization of KCN-responsive areas and their correlation with escape behavior. Accordingly, here we compared the brainstem activations of saline-injected controls (air/saline) with those produced by a single intravenous injection of 40-µg KCN (air/KCN), a 2-min exposure to 13% CO2 (CO2/saline), or a combined stimulus (CO2/KCN). Behavioral effects of KCN microinjections into the PAG were assessed as well. Data showed that whereas the KCN microinjections were ineffective, KCN intravenous injections elicited escape in all tested rats. Moreover, whereas the CO2 alone was ineffective, it potentiated the KCN-evoked escape. Compared to controls, the nucleus tractus solitarius was significantly activated in both CO2/saline and CO2/KCN groups. Additionally, whereas the laterodorsal tegmental nucleus was activated by all treatments, the rostrolateral and caudoventrolateral PAG were activated by air/KCN only. Data suggest that the latter structures are key components of a hypoxia-sensitive suffocation alarm which activation may trigger a panic attack.

Ventral hippocampus modulates bradycardic response to peripheral chemoreflex activation in awake rats.

What is the central question of this study? Does reversible synaptic inactivation by CoCl2 in the dorsal (DH) or ventral (VH) portions of the hippocampus have a modulatory effect on cardiovascular and respiratory responses evoked by chemoreflex activation in awake rats? What is the main finding and its importance? Using i.v. infusion of KCN to activate the peripheral chemoreflex before and after microinjection of CoCl2 into VH, we showed that the bradycardic response was increased, but not the pressor and tachypnoeic responses even if the tidal volume had been increased. Thus, VH but not DH may be involved in the modulation of the parasympathoexcitatory component of the peripheral chemoreflex. In rats, peripheral chemoreflex activation evokes pressor and bradycardic responses as well as a tachypnoeic response. Studies have shown that limbic structures, such as the hippocampus, can modulate autonomic reflexes. Evidence suggests that the dorsal (DH) and the ventral (VH) portions of the hippocampus are structurally and functionally distinct; therefore, in the present study we tested the hypothesis that local neurotransmission of the DH and VH are involved in the neural pathways of the cardiovascular and ventilatory responses to chemoreflex activation. Thus, the goal of the present study was to compare the chemoreflex responses elicited by i.v. injection of KCN (40μg per rat) in awake rats before and after DH and VH synaptic transmission was temporarily inhibited by bilateral microinjections of 500nl of the unspecific synapse blocker, CoCl2 (1 mm). Bilateral inhibition of VH, but not DH, 10min before KCN infusion was able to enhance the bradycardic response (P<0.05), with no changes in the typical pressor and tachypnoeic responses evoked by chemoreflex activation (P>0.05). Furthermore, the tidal volume was significantly increased (P<0.05) even though no other respiratory parameter had been significantly changed (P>0.05), suggesting that VH can exert a tonic modulatory action on tidal volume. Therefore, the present study reports, for the first time, that DH neurotransmission did not exert an influence on chemoreflex responses, whereas VH mediates, at least in part, the parasympathoexcitatory component of the peripheral chemoreflex.

Chemoreflex and baroreflex alterations in Parkinsonism induced by 6-OHDA in unanesthetized rats

Parkinson’s disease (PD) is mainly characterized by motor signals. However, non-motor signals also affect and decrease the quality of life of PD patients. Among these non-motor signs are cardiovascular disorders as orthostatic hypotension, postprandial hypotension and cardiac arrhythmias, which may be due to the involvement of both central nervous system and peripheral autonomic nervous system. In the present study we investigated the cardiovascular function, evaluating cardiovascular reflexes (chemoreflex and baroreflex), in an animal model of Parkinsonism induced by bilateral infusion of the toxin 6-hydroxydopamine (6-OHDA), in the substantia nigra pars compacta (SNpc). The results showed that the animals induced to Parkinsonism had lower arterial pressure (AP) and heart rate HR) compared to control animals. We showed that after activation of the baroreceptors by phenylephrine (Phe) and sodium nitroprusside (SNP), the baroreflex sensitivity index was not changed between the groups. However, there was a greater increase in the AP when stimulated with Phe and greater tachycardia when stimulated with SNP in 6-OHDA animals. After activation of the peripheral chemoreceptors through KCN injection (cytotoxic hypoxia), there was a higher increase in pressor and bradycardic response in injured animals with bilateral 6-OHDA. These changes in the cardiovascular reflexes may be important adjustments mechanisms to maintain the cerebral blood flow in those animals, and may be a result of denervation supersensitivity to catecholamines in autonomic targets.

Effects of &lt;i&gt;Alium cepa Linn&lt;/i&gt; on rhodanese activities and half-life of cyanide in the blood

Rhodanese is the major detoxifying enzyme for cyanide and requires sulphur for its action. Allium cepa (Onion) is rich in organosulphur which may serve as an antidote for cyanide poisoning by supplying sulphur to the enzyme rhodanese. The possible effects of Allium cepa on rhodanese activity during cyanide toxicity was investigated in male Wistar rats. Sixty Wistar rats (150-180 g) were divided into ten groups of six rats each. The first six groups were used for in vivo rhodanese activities evaluation after treatments orally with either KCN (7 mg/kg bwt/day KCN), KCN+300 mg Methanol Extract of Allium cepa (MEAC)/kg bwt/day, KCN+600 mg MEAC/kg bwt/day, KCN+ 600 mg sodium thiosulphate (Na2S2O3) /kg bwt/day or 600 mg MEAC /kg bwt/day respectively. The last four groups were used for the evaluation of half-life of KCN after treatment orally with distilled water (control), 600 mg MEAC/kg bwt/day, 600 mg Na2S2O3/kg bwt/day and raw onion adlibitum respectively for two weeks before intravenous injection of KCN. In vitro rhodanese activity was determined using liver homogenate. Results of the in vivo study showed liver rhodanese activity was significantly higher (p<0.05) in the cyanide only group and in the cyanide + Na2S2O3 group when compared with the control group, but administration of MEAC in the cyanide treated group did not enhance the activities of rhodanese. The results of the in vitro study showed that rhodanese activity was more enhanced in the presence of essential oil of onion and Na 2 S 2 O 3 . The half-life of KCN was significantly lower (p<0.05) with consumption of raw onion when compared with control. The results suggest that Allium cepa enhance cyanide detoxification by enhancing rhodanese enzyme activities. This effect is more pronounced with the essential oil of onion.

Chemoreflex control of the cardiovascular system remains altered after recovery from low protein diet early in life.

This study aimed to evaluate the cardiovascular component of the arterial chemoreflex in rats recovered from low protein diet. Male Fischer rats were randomly divided into control and recovered (R-PR) groups after weaning. R-PR rats were fed with low protein diet for 35days and recovered under normal protein diet for 70days. Control rats received normal protein diet for 105days. Arterial chemoreflex was elicited by intravenous injection of KCN. Results showed that pressor response of the chemoreflex was increased in R-PR. Data suggest that protein restriction may alter cardiovascular response to chemical activation of the chemoreflex after recovery.

Systemic administration of leptin potentiates the response of neurons in the nucleus of the solitary tract to chemoreceptor activation in the rat

Leptin microinjections into the nucleus of the solitary tract (NTS) have been shown to elicit sympathoexcitatory responses, and potentiate the cardiovascular responses to activation of the chemoreflex. In this study, experiments were done in Sprague–Dawley rats initially to provide a detailed mapping within the NTS complex of cells containing immunoreactivity to the long form of the leptin receptor (Ob-Rb). In a second series, this NTS region containing Ob-Rb immunoreactive cells was explored for single units antidromically activated by stimulation of pressor sites in the rostral ventrolateral medulla (RVLM). These antidromically identified neurons were then tested for their response to intra-carotid injections of leptin (50–100ng/0.1ml), and to activation of peripheral chemoreceptors following an injection of potassium cyanide (KCN) (80μg/0.1ml) into the carotid artery. Cells containing Ob-Rb-like immunoreactivity were found predominantly in the caudal NTS: within the medial, commissural and gelatinous (sub-postremal area) subnuclei of the NTS complex. Of 73 single units tested in these NTS regions, 48 were antidromically activated by stimulation of RVLM pressor sites and 25 of these single units responded with an increase in discharge rate after intra-carotid injections of leptin. In addition, 17 of these leptin responsive neurons were excited by the intra-carotid injections of KCN (80μg/0.1ml). Furthermore, the excitatory response of these single units to KCN was potentiated (59–83%) immediately following the leptin injection. These data indicate that leptin responsive neurons in NTS mediate chemoreceptor afferent information to pressor sites in the RVLM, and suggest that leptin may act as a facilitator on neuronal circuits within the NTS that potentiates the sympathoexcitatory responses elicited during the reflex activation of arterial chemoreceptors.

Fos expression in the NTS in response to peripheral chemoreflex activation in awake rats

Chemoreflex afferent fibers terminate in the nucleus tractus solitarii (NTS), but the specific location of the NTS neurons excited by peripheral chemoreflex activation remains to be characterized. Here, the topographic distribution of chemoreflex sensitive cells at the commissural NTS was evaluated. To reach this goal, Fos-immunoreactive neurons (Fos-ir) were accounted in rostro-caudal levels of the intermediate and caudal commissural NTS, after intermittent chemoreflex activation with intravenous injection of potassium cyanide [KCN (80 μg/kg) or saline (0.9%, vehicle), one injection every 3 min during 30 min]. In response to intermittent intravenous injections of KCN, a significant increase in the number of Fos-ir neurons was observed specifically in the lateral intermediate commissural NTS [ LINTS (82 ± 9 vs. 174 ± 16, cell number mean per section)] and lateral caudal commissural NTS [ LCNTS (71 ± 9 vs. 199 ± 18, cell number mean per section)]. To evaluate the influence of baroreceptor-mediated inputs following the increase in blood pressure during intermittent chemoreflex activation, we performed an intermittent activation of the arterial baroreflex by intravenous injection of phenylephrine [1.5 μg/kg iv (one injection every 3 min during 30 min)]. This procedure induced no change in Fos-ir in LINTS (64 ± 6 vs. 62 ± 12, cell number mean per section) or LCNTS (56 ± 15 vs. 77 ± 12, cell number mean per section). These data support the involvement of the commissural NTS in the processing of peripheral chemoreflex, and provide a detailed characterization of the topographical distribution of activated neurons within this brain region.

ACTIVATION OF PERIPHERAL CHEMORECEPTORS CAUSES POSITIVE INOTROPIC EFFECTS IN A WORKING HEART–BRAINSTEM PREPARATION OF THE RAT

1. The aim of the present study was to evaluate the effects of peripheral chemoreceptor activation on myocardial contractility in an anaesthetic-free decerebrated rat preparation. 2. In the decerebrated and retrogradely perfused working heart-brainstem preparation, we recorded phrenic nerve activity, left ventricular (LV) pressure (microtip Millar catheter), LV dP/dT, heart rate and aortic perfusion pressure before and after activating peripheral chemoreceptors with bolus intra-arterial injections of KCN. 3. Without cardiac pacing, chemoreflex activation caused falls in heart rate (-108 +/- 21 b.p.m.) and complex polyphasic changes in LV pressure and LV dP/dT. If the heart was paced, chemoreflex activation caused significant rises in LP pressure (+16 +/- 3 mmHg) and LV dP/dt (+778 +/- 93 mmHg/s). These positive inotropic effects were significantly and substantially attenuated by beta-adrenoceptor blockade with atenolol. In all instances, chemoreflex activation elicited potent tachypnoeic responses. 4. In conclusion, activation of peripheral chemoreceptors in non-anaesthetized rats evokes a positive inotropic response that is sympathetically mediated. This observation may be relevant for the evaluation of neurally induced effects of acute hypoxia on the ventricular myocardium.

Cardiovascular responses to chemoreflex activation with potassium cyanide or hypoxic hypoxia in awake rats

Although intravenous (iv) injection of potassium cyanide (KCN) activates the arterial chemoreflex, it has been questioned whether cytotoxic hypoxia reproduces a physiological stimulus such as hypoxic hypoxia (low inspired O 2 tension). Thus, the goal of the present study was to compare the cardiovascular responses elicited by intravenous injection of KCN to those caused by hypoxic hypoxia in awake rats before and after bilateral ligature of carotid body arteries. We tested the hypothesis that hypoxic hypoxia activates the cardiovascular chemoreflex just as KCN does, causing an increase in arterial pressure and bradycardia. Intact adult Wistar rats received an intravenous injection of KCN (160 μg/kg) and were exposed to hypoxic hypoxia (7–5% O 2 breathing) for 10–15 s at random while mean arterial pressure (MAP) and heart rate (HR) were measured. After the experiments, the animals were submitted to bilateral ligature of carotid body arteries or sham operation and the protocol was repeated on the subsequent day. Before surgery, all rats showed an abrupt rise in arterial pressure accompanied by a marked bradycardia in response to KCN or hypoxic hypoxia, with a very similar pattern. After surgery, these responses persisted only in the sham-operated group and were totally abolished in the ligature group. In conclusion, our data show that KCN is an appropriate stimulus to activate arterial chemoreflex because its cardiovascular responses are comparable to those induced by hypoxic hypoxia. Thus, the use of KCN as a tool to evaluate different aspects of the complex pattern of cardiovascular, respiratory, and behavioural responses to chemoreflex activation seems to be physiologically acceptable.

Brief Communication EFFECTS OF MELATONIN ON KCN-INDUCED NEURODEGENERATION IN MICE

Melatonin is known to have a neuroprotective effect by preventing epileptic seizures, which are normally induced by cyanide. To demonstrate the neuroprotective function of melatonin, we examined cell death and changes in plasma melatonin level in KCN-treated mice. Neuronal cell death is shown in substantial nigra of KCN-treated groups. In melatonin-treated groups, this cell death decreased in substantia nigra. Plasma melatonin level at 12:00 was significantly decreased to 52.6% after KCN injection as compared to the normal group. In contrast, melatonin level was significantly decreased (74.5%) in KCN + melatonin group. Melatonin level at 24:00 was significantly decreased to 57.0% after KCN injection and also significantly decreased to 81.0% in KCN-melatonin group as compared to the normal group. Results from the present study suggest that melatonin prevents neuronal cell death in KCN-induced brain.

Peripheral chemoreceptor activation enhances 5-hydroxytryptamine release in the locus coeruleus of conscious rats

Intravenous bolus injection of KCN (40 μg) elicited brief but pronounced tachypnea, bradycardia and pressor response, and led to a 37% increase in 5-hydroxytryptamine (serotonin) (5-HT) release in the locus coeruleus (LC) of freely moving rats. Slow infusion of KCN (15 μg/min) for 10 min induced only a slight pressor response, but increased the respiration rate (+39 breaths/min), as well as 5-HT release in the LC (+60%) throughout the infusion. In rats with transected chemoreceptor afferents, neither injection or infusion of KCN changed 5-HT release, suggesting that in intact animals, the effect on extracellular 5-HT was due to activation of peripheral chemoreceptors. In summary, we report that peripheral chemoreceptor activation enhances 5-HT release in the LC, indicating that 5-HT might be involved in the modulation of LC activity by ascending chemosensory information.

Chemical control of laryngeal vascular resistance in anesthetized dogs.

The branch of the cranial superior thyroid artery that supplies the larynx was perfused unilaterally at a constant flow rate in dogs anesthetized with pentobarbitone sodium (30 mg.kg-1, i.v.). Laryngeal vascular resistance (RLv) was calculated. Intraluminal laryngeal pressure (PL) was determined. Asphyxia caused a diminution in PL (-27.7 +/- 4.2%) (p < 0.01) and an initial decrease followed by an increase in RLv (-10.9 +/- 2.3% and +12.8 + 2.8%) (p < 0.001). Following vagotomy, asphyxia decreased PL (-17.1 +/- 4.2%) and increased RLv (+45.5 +/- 11.0%). Systemic hypoxia induced by breathing 8% O2-N2 increased RLv (+8.4 +/- 1.3%) (p < 0.001) and decreased PL (-24.9 +/- 3.7%) (p < 0.001). In chemodenervated dogs, the response of PL to hypoxia was abolished while that of RLv was similar to that in intact animals. Breathing of 7% CO2 in air caused an increase in RLv (+6.1 +/- 1.6%) (p < 0.001) and a decrease in PL (-20.9 +/- 3.2%) (p < 0.001). Following chemodenervation, hypercapnia still increased RLv (+11.3 +/- 3.2%) (p < 0.01) and diminished PL (-29.9 +/- 2.5%). Bilateral vagotomy reduced the response of PL to hypercapnia (-13.3 +/- 6.9%) (p < 0.05). Local intra-arterial injection of KCN produced an increase in RLv and PL (+7.0 +/- 1.2%, +9.0 +/- 1.0%). After peripheral chemodenervation KCN injection slightly increased PL (+2.0 +/- 0.9%). The response of RLv was almost abolished. In conclusion, laryngeal vasoconstriction in response to systemic hypoxia after chemodenervation is probably mediated by increased sympathetic discharge to the larynx due to hypoxia of the CNS. Laryngeal responses to hypercapnia may be due to the action of central chemoreceptors.

Fast glycolytic oscillations induced by potassium cyanide in the brain of behaving rats (potentiometric recording)

Earlier the probability for the occurrence of quasisinusoidal oscillations in the mammal's brain redox-state potential ( E) (4–20 osc/min) recorded by an implanted platinum electrode has been shown to rise during high levels of behavior arousal [T.B. Shvets-Teneta-Gurii, K.Ju. Sarkisova, Change in oxidation–reduction potential of cerebral structures in the rat during paradoxical sleep, Translated from Dokl. Akad. Nauk SSSR 309 (1989) 1256–1259, Plenum, 1990; T.B. Shvets-Teneta-Gurii, V.N. Maz, O.B. Kovchegova, Rhythms of slow wave sleep and wakefulness in oscillations of the cerebral cortical redox potential, Bull. Exp. Biol. Med. 108 (1990) 1209–1211; T.B. Shvets-Teneta-Gurii, The rabbit's brain cortex redox-state potential in the course of hypnosis (immobilization stress), Dokl. USSR Acad. Nauk. 315 (1990) 1014–1017]. We supposed these oscillations to be generated by oscillations of the redox balance in glycolytic paths developing during a sharp increase in glycolysis rate similar to those described for populations of microorganism [A. Betz, B. Chance, Influence of inhibitors and temperature on the oscillations of reduced pyridine nucleotide in yeast cells, Arch. Biochem. Biophys. 109 (1965) 579–586]. To test the supposition, modelling experiments were done in which the classical method was used to increase glycolysis rate and to make glycolytic oscillations in the brain of a behaving rat by inhibition of the tissue respiration by KCN. It has been found that KCN injection (5–7 mg/kg, intraperitoneally (i/p), rats) induced within 10–20 min a significant decrease (for 15–150 mV) of the local brain E, and a chain of damped quasisinusoidal oscillations (frequency 4–12 osc/min, amplitude 0.5–10 mV) could occur in the local brain E for 3–15 min after KCN injection. These data suggest that the glycolytic oscillations could be one of the sources of the brain-event-related E oscillations monitored by the implanted platinum electrode.

Commissural NTS contributes to pressor responses to glutamate injected into the medial NTS of awake rats.

In the present study we investigated whether interruption of the chemoreceptor reflex by an electrolytic lesion of the commissural subnucleus of the nucleus tractus solitarii (commNTS) influenced pressor and bradycardic responses induced by microinjection of L-glutamate (L-Glu) into the medial NTS (mNTS) of conscious rats. Seven days after sham lesions, seven rats demonstrated significant pressor [change in mean arterial pressure (MAP) = +33 +/- 3 mmHg] and bradycardic [change in heart rate (HR) = -74 +/- 8 beats/min (bpm)] responses to chemoreceptor reflex activation by intravenous injection of KCN. Likewise, L-Glu (1 nmol in 100 nl) injected into the mNTS in sham rats induced pressor (+29 +/- 2 mmHg) and bradycardic responses (-90 +/- 8 bpm). However, in 11 rats with lesions in commNTS, pressor and bradycardic chemoreceptor reflex responses were abolished, and injection of L-Glu into the mNTS decreased MAP (-14 +/- 6 mmHg) and HR (-59 +/- 16 bpm) as is reported in anesthetized control rats. We conclude that pressor responses induced by L-Glu microinjected into the baroreceptor reflex region of mNTS in conscious rats depend on the integrity of the commNTS, which plays an important role in central chemoreceptor reflex pathways.

MK-801 prevents cyanide-induced changes of Fos levels in rat brain.

The effect of acute cyanide intoxication on levels of transcriptional regulatory proteins Fos and c-Jun in rat cortex, hippocampus, cerebellum and brain stem was studied. Western blot analysis showed a differential effect of cyanide on Fos levels in the selected brain areas. The most prominent changes were seen 60 min. following ip. injection of KCN in all brain areas except the brain stem, which showed the maximal change 120 min. following cyanide. Fos levels were doubled in cortex and cerebellum and decreased to below 70% of the control levels in hippocampus. Levels of c-Jun were not altered 60 min. following cyanide treatment. Pretreatment with the NMDA receptor antagonist, MK-801, prevented the cyanide-induced changes of Fos. The differential effect of cyanide on Fos levels in different brain areas and the blockade of these changes by MK-801 suggest involvement of multiple neuronal pathways, including the excitatory amino acid (EAA) neurotransmitter system. It is concluded that cyanide alters levels of the transcriptional regulatory protein Fos through activation of the EAA neurotransmitter system and, thus, may affect gene expression in neuronal or glia cells.