Role of central and peripheral mechanisms in control of excitability of segmental motor centers in insects

The role of central and peripheral mechanisms in control of excitability of segmental centers providing different motor acts in insects of phylogenic close orders, but differing by the level of activity of their locomotor systems has been studied in the locust Locusta migratoria and the cockroach Periplaneta americana. It was shown that the level of relative excitability of segmental centers in cockroaches seemed to be much determined by the peripheral mechanisms, but not by the central mechanisms as in locust. It is suggested that control of activity of segmental locomotor centers from the higher parts of CNS can be realized by different ways: predominantly via excitatory or inhibitory influences on activity id some particular locomotor systems depending on their role and significance in motor behavior of these animals.Translated from Zhurnal Evolyutsionnoi Biokhimii i Fiziologii, Vol. 40, No. 6, 2004, pp. 508–513.Original Russian Text Copyright © 2004 by Gorelkin, Severina.To the 100-Anniversary of A. K. VoskresenskayaThis revised version was published online in April 2005 with a corrected cover date.     

Role of peripheral and central chemoreceptors in the initiation of fetal respiration.

The relationship between fetal femoral arterial P02 and PC02 was evalulated in 13 fetal sheep with intact and denervated peripheral chemoreceptors. With intact chemoreceptors, a significant relationship was found between fetal Pa02 and PaC02 at the time of the first breath (Pa02 = 2.57 + 0.09 PaC02; r = 0.62, P less than 0.05)mfollowing bilateral carotid sinus nerve section (CSN) or total peripheral chemodenervation (TD), PaC02. Comparison of the intact, CSN, and TD blood gases at the time of the first breath demonstrated that a) severe hypoxemia stimulates fetal respiration even following total peripheral chemodenervation; b) fetal central chemoreceptors do not respond to PaC02; c) PaC02 acting via peripheral chemoreceptors has a minor modulating effect on the degree of hypoxemia required to initiate fetal respiration. At a PaC02 below 40 mmHg this effect is inhibitory, acting via the carotid body. At a PaC02 above 90 mmHg this effect is stimulatory, acting via both carotid and aortic bodies.     

Participation of dopamine in regulation of respiration

Conclusions The data obtained during a rather long period of time and reported in the literature suggest that dopamine plays an independent role in the organism, being involved in regulation of the most important functions. The question about the place of dopamine in reception of the oxygen level in the peripheral and central mechanisms that regulate respiration needs further investigation. This question possibly is tightly related to the different sensitivity of various groups and subgroups of dopamine receptors, their spatial distribution and their ability to change their affinity for ligands depending on the environment. This determines a dose-dependent pattern of the effects of dopamine receptor activation and strong dependence of the effects on other experimental conditions.     

Role of activity-dependent mechanisms in the control of dopaminergic neuron survival

Dopaminergic neurons that constitute the nigrostriatal pathway are characterized by singular electrical properties that allow them to discharge in vivo spontaneously in a spectrum of patterns ranging from pacemaker to random and bursting modes. These electrophysiological features allow dopaminergic neurons to optimize the release of dopamine in their terminal fields. However, there is emerging evidence indicating that electrical activity might also participate in the control of dopaminergic neuron survival, not only during development, but also in the adult brain, thus raising the possibility that alterations in ionic currents could contribute actively to the demise of these neurons in Parkinson disease. This review focuses on the mechanisms by which activity-dependent mechanisms might modulate dopaminergic cell survival.     

Role of betaine in the control of respiration and osmoregulation of a halotolerant bacterium

Abstract This review deals with work on some aspects of halotolerance carried out in our laboratory. The organism used throughout these investigations is a halotolerant, obligate aerobic rod, designated as Ba₁. Attention is focused on the effect of osmotic stress on respiratory rate, since under the conditions tested the latter is rate-limiting for growth. Under hyperosmotic conditions there is a steep drop in the rate of oxygen uptake, but the inhibition can be relieved by betaine. Two major factors seem to be involved in this effect of betaine: (a) Iso-osmotic adaptation due to its accumulation in the cytosol (deplasmolysis); (b) facilitation of the penetration of Na⁺ into plasmolysed cells. Na⁺ is required for the proper functioning of the respiratory chain. Na⁺ probably enters the cells in symport with betaine, whereas an excess of this cytotoxic cation is extruded by a powerful primary Na⁺ pump which is found to operate in Ba₁. Such a pump has also been identified in another halotolerant organism, Vibrio alginolyticus . In both micro-organisms the site of Na⁺-stimulation corresponds to the site of Na⁺ translocation.     

Involvement of cholinergic mechanisms in the central control of respiration in the cane toad, Bufo marinus

Chemical substrates, central sites and central mechanisms underlying the regulation of breathing in lower vertebrates have not been well characterized. The present study was undertaken to determine the effect of pH changes and cholinergic agents on the central control of respiration in the cane toad, Bufo marinus. Adult toads were anesthetized, catheterized and unidirectionally ventilated before exposing the brainstem. An airtight buccal cannula was also inserted through the tympanum to record buccal pressure. The animal was decerebrated, anesthetic removed and the responses to pH changes of solutions bathing the ventral surface of the medulla (VSM) were tested by superfusing the VSM with mock cerebrospinal fluid (mCSF) of pH 7.8-normal, 7.2-acidic and 8.4-basic. The acidic solution increased respiratory activity, the basic solution decreased activity and the normal solution had no effect. In addition, cholinergeric agents (acetylcholine-ACh, physostigmine-Phy, nicotine-Nic, and atropine-Atr) dissolved in mCSF were applied bilaterally onto the VSM using filter paper pledgets. ACh, Phy and Nic increased episodic breathing frequency by 14.3+/-9.7, 9.4+/-5.4 and 29.1+/-11.8 %, respectively, whereas, Atr caused a decrease (-26.6+/-16.6%). These agents had no effect on blood pressure. It is therefore, concluded that the VSM is pH sensitive and a cholinergic mechanism is involved in the central modulation of respiration in Bufo.     

Role of pressor mechanisms from the NTS and CVLM in control of arterial pressure

In the present study, we investigated the effects of inhibition of the caudal ventrolateral medulla (CVLM) with the GABA(A) agonist muscimol combined with the blockade of glutamatergic mechanism in the nucleus of the solitary tract (NTS) with kynurenic acid (kyn) on mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances. In male Holtzman rats anesthetized intravenously with urethane/chloralose, bilateral injections of muscimol (120 pmol) into the CVLM or bilateral injections of kyn (2.7 nmol) into the NTS alone increased MAP to 186 +/- 11 and to 142 +/- 6 mmHg, respectively, vs. control: 105 +/- 4 mmHg; HR to 407 +/- 15 and to 412 +/- 18 beats per minute (bpm), respectively, vs. control: 352 +/- 12 bpm; and renal, mesenteric and hindquarter vascular resistances. However, in rats with the CVLM bilaterally blocked by muscimol, additional injections of kyn into the NTS reduced MAP to 88 +/- 5 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Moreover, in rats with the glutamatergic mechanisms of the NTS blocked by bilateral injections of kyn, additional injections of muscimol into the CVLM also reduced MAP to 92 +/- 2 mmHg and mesenteric and hindquarter vascular resistances below control baseline levels. Simultaneous blockade of NTS and CVLM did not modify the increase in HR but also abolished the increase in renal vascular resistance produced by each treatment alone. The results suggest that important pressor mechanisms arise from the NTS and CVLM to control vascular resistance and arterial pressure under the conditions of the present study.     

Role of the presynaptic receptors in the control of dopamine synthesis in the striate complex and nucleus accumbens

The role of presynaptic receptors on dopamine synthesis, at both nigrostriatal and mesolimbic systems, has been studied after dopamine uptake drastically increases the dopamine and DOPAC levels at n. accumbens but not at striatum. The present data suggest that presynaptic receptors are a decisive factor regulating dopamine synthesis at nigrostriatal system. However, the end-product inhibition could be the most important autoregulatory mechanism at the mesolimbic system.     

Role of DopR in the molecular mechanism of the dopamine control of juvenile hormone metabolism in female Drosophila

The effect of a decreased availability of the D1-like dopamine receptor (DopR) in Drosophila (caused by DopR antagonist added into food) on the juvenile hormone (JH) synthesis rate in young female D. melanogaster has been studied. The JH degradation rate and the alkaline phosphatase (ALP) and tyrosine decarboxylase (TDC) activities were used as indicators of the JH synthesis rate. Treatment of the flies with butaclamol, a specific DopR antagonist, has been demonstrated to increase the JH degradation rate, and the stress reactivity of the system of JH metabolism and to decrease the ALP activity and stress reactivity, and to increase the TDC activity and stress reactivity. As shown earlier, all this indicates a decrease in the JH synthesis rate in young female drosophila with a decreased DopR availability. It is concluded that the activating effect of dopamine on JH synthesis in Drosophila is mediated by D1-like receptors.     

Nervous control of respiration

Century-old notions on and formulations of the principle of external respiration control are discussed. The development of the main views on the mechanisms of action of individual nervous structures involved in respiratory control and their contributions is analyzed. A generalized scheme of the respiratory system control is proposed, according to which this autonomic and somatic system is composed of strictly defined afferent, central, and efferent components and is an open, multiextremal, adaptive, self-learning system based on a hierarchical principle. Ultimately, under any conditions of the vital activity of the body, the main regulator of the system (the respiratory center) optimally performs both deviation and perturbation control.     

Resistive loading and mechanisms regulating respiration

In experiments on anesthetized cats, switch on of additional inelastic respiration resistance (resistive load) produced, apart from slowing of the respiratory flows, an increase in the activity of motoneurons and inspiratory intrathoracic pressure. Bilateral vagotomy resulted in disappearance of resistive load-induced elevation of the phrenic nerve activity, but did not abolish the growth of the inspiratory effort. Analysis of the evidence obtained indicates that activation of phrenic motoneurons associated with increased respiration resistance is underlain by prolongation of the inspiratory phase that is consequent on relaxation of the inspiratory inhibition. It is suggested that, in addition to the mechanism depicted, the compensatory reaction to the resistive load involves, apart from diaphragm participation, other inspiratory muscles as well as enhanced contractions of respiratory muscles provided by the properties of muscular fiber.