Participation of the opioid- and serotonergic systems of the ventrolateral medullary regions in the control of respiratory activity in early postnatal rats

The effects of blockers of opioid and serotonin receptors (naloxone and methisergide, respectively) on the respiratory activity recorded from then. phrenicus of semi-isolated medullo-spinal preparations (SIMSP) were studied in newborn (1-day-old) and 4- to 5-day-old rats. The preparations were superfusedin situ, and inspiratory discharges (ID) were recorded before and after transverse sections of the ventrolateral medullary regions (VLMR) at different levels. Naloxone evoked an increase in the ID frequency in then. phrenicus both at the initial configuration of preparations and after successive transections of the VLMR between theM andS chemosensitive zones and between theS andL zones. The relative intensity of this effect was significantly higher in newborn rats than in 4- to 5-day-old ones. In contrast, methisergide made the ID frequency lower at all configurations of the SIMSP, and this effect was more intensive in 4- to 5-day-old animals. In the course of progressive separations of more rostral VLMR zones, the effects of naloxone and methisergide applications on the ID frequency became weaker. This allows us to suppose that in newborn rats the rostral VLMR portions provide more intensive opioidergic inhibitory control influences on the activity of respiratory networks than those in 4- to 5-day-old animals. At the same time, tonic activating influences from serotonergic VLMR neurons on the mechanisms generating respiratory rhythm are more intensive in 4- to 5-day-old animals than those in newborn ones. Thus, it can be supposed that the levels of maturation of the opioid- and serotonergic neurotransmitter systems, which provide tonic control of respiratory activity generated in the VLMR, are different in newborn and 4- to 5-day-old animals. The problems of how the opioid- and serotonergic mechanisms controlling respiratory rhythm generation are formed in the course of early stages of ontogenetic development are discussed.Neirofiziologiya/Neurophysiology, Vol. 28, No. 1, pp. 62–73, January–February, 1996.     

Parameters of discharges of respiratory neurons of the ventrolateral medullary regions in early postnatal rats

In experiments on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of newborn (1st day of life) and 4- to 5-day-old rats, we studied the parameters of extracellularly recorded spike activity of respiratory neurons of the ventrolateral medullary regions (VLMR). In SIMSP of 4- to 5-day-old rats, the frequency of discharges of pre-inspiratory, inspiratory, and expiratory neurons is shown to be significantly higher, while the dispersion of its values is considerably lower, as compared with the corresponding values for newborn animals. In the majority of pre-inspiratory and inspiratory neurons of SIMSP of newborn rats, irregular low-frequency discharges are usually generated within the interinspiration phase. The relative intensity of suppression of discharges of pre-inspiratory and expiratory neurons within an inspiration phase is much lower in SIMSP of newborn rats, as compared with that in 4- to 5-day-old preparations. The activity of most pre-inspiratory neurons manifests a trend toward transformation from a two-phase pattern in newborn rats (with two frequency peaks, pre- and post-inspiratory) to a monophasic pattern (with one pre-inspiratory frequency peak) typical of 4- to 5-day-old animals. The effects of electrical stimulation of the site of localization of pre-inspiratory neurons showed that in SIMSP of both age groups of rats an inspiratory response could be evoked in then. phrenicus only in the case when stimulation was applied within the second half of an interinspiratory phase. Therefore, it can be supposed that the respiratory network in newborn animals is to a considerable extent immature in the morphofunctional aspect. It seems probable that in early postnatal rats pre-inspiratory neurons are involved in the medullary mechanisms foron-off switching of the inspiratory and expiratory phases.Neirofiziologiya/Neurophysiology, Vol. 28, No. 4/5, pp. 207–217, July–October, 1996.     

Effects of hypoxia on the respiratory activity generated by semi-isolated medullo-spinal preparations of early postnatal rats

The effects of short- and long-lasting (2-min-long and up to 30-min-long) hypoxia episodes on the inspiratory activity (IA) recorded from then. phrenicus were tested in experiments on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of newborn (the lst day of life) and 4- to 5-day-old rats. Hypoxia was provided by superfusion of the preparations with low-O₂ solution. Short-lasting hypoxia evoked no significant modulation of the IA in preparations of newborn animals, while two-phase responses (an initial, up to 30 sec, increase in the frequency of inspiratory discharges, followed by their longer, up to 4 min, suppression) were observed in 4- to 5-day-old preparations. Long-lasting hypoxia suppressed activity in then. phrenicus of 1-day-old preparations, and this effect was replaced in five cases by the development of sporadic low-amplitude and short-lasting inspiratory discharges. These shortened discharges were qualified as gasps. The responses of 4- to 5-day-old SIMSP to long-lasting hypoxia episodes were more complex. An initial increase in the IA frequency lasted up to 30 sec, and in 4–6 min it was followed by complete suppression of the activity. In some of the SIMSP, permanent tonic activity appeared in then. phrenicus within the period of total absence of inspiratory discharges, which could be followed by generation of short low-amplitude gasping discharges. Against the background of gasping pattern, eupnoe-like discharges appeared in four preparations. Under control conditions, transerve section of the ventrolateral medullary regions (VLMR) at a middle level of then. hypoglossus root abolished respiratory activity in all studied SIMSP. Yet, in some of the SIMSP of both newborn and 4- to 5-day-old animals long-lasting hypoxia testing evoked weak tonic activity in then. phrenicus followed by the appearance of gasping discharges. After the transection of the VLMR at the caudal edge of then. hypoglossus root, long-lasting hypoxia evoked only weak tonic responses in some SIMSP of both age groups, and there were no phasic discharges in this case. The results of our experiments, first, show that the respiratory activity in newborn animals is more resistant to hypoxia than that in 4-to 5-day-old rats, and, second, they allow us to suppose that the gasp-generating medullary structures are localized in more caudal medullary regions. We discuss the questions of how the eupnoe-generating and gasp-generating medullary structures are formed in rats during their initial four to five postnatal days, and what specific features are typical of hypoxia-related respiratory responses in these animals.Neirofiziologiya/Neurophysiology, Vol. 28, No. 2/3, pp. 121–131, March–June, 1996.     

Effect of nitric oxide on the respiratory activity generated under hypoxic conditions by medullo-spinal preparations from early postnatal rats

Experiments on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of 3- to 4-day-old rats were carried out to study the effects of a blocker of nitric oxide synthase (NO synthase), methyl ester of N^G-nitro-L-arginine (MENA), and an exogenic NO donor, nitroglycerin, on the respiratory activity. Inspiratory discharges (ID) were recorded from the phrenic nerve under superfusion of SIMSP with a standard saline and a solution saturated with anoxic isocapnic gas mixture. Under normal conditions, 3-min-long applications of 1.0 μM MENA evoked no significant changes in the parameters of inspiratory activity; yet 10.0 μM of this blocker evoked a significant drop in the amplitude and an increase in the ID frequency. Three-min-long applications of 1.0 μM nitroglycerin significantly decreased the ID frequency and somewhat increased their amplitude and integral intensity. Higher doses of nitroglycerin (10.0 μM) significantly increased the amplitude and integral intensity of ID and in a lesser extent lowered their frequency. Under conditions of 3-min-long hypoxia, 10-min-long preliminary superfusion of SIMSP with the 1.0 μM MENA-containing saline resulted in no significant changes of respiratory activity, as compared with the hypoxia effect in the norm. Applied before the hypoxic test, 10 μM MENA resulted in significant decreases in the amplitude and integral intensity of ID; concurrently their frequency became higher, as compared with the respective parameters measured at hypoxic testing of the intact preparations. Ten-min-long superfusion with 1.0 μM nitroglycerin-containing solution at subsequent hypoxic testing significantly increased the amplitude and integral intensity of ID and decreased their frequency; these shifts developed during the first half of exposure to the hypoxic solution. Increased (to 10 μM) nitroglycerin concentration resulted in less intensive shifts in the ID frequency within the first half of a hypoxic episode. In a part of the tests, the second half of exposure of SIMSP to the hypoxic solution was characterized by the appearance of low-amplitude short ID against the background of suppressed eupnea-like respiratory activity; we qualified such discharges as gasping discharges. The experimental data confirm the involvement, of NO in the central regulation of the frequency and amplitude parameters of inspiratory activity generated by SIMSP of early postnatal rats both under normoxic and hypoxic conditions. The role NO plays under hypoxic conditions in modifications of parameters of respiratory activity and in modulation of the functional, levels of the bulbar respiratory generator is discussed.     

Involvement of NMDA receptors in the control of respiratory rhythm generated by medullo-spinal preparations of early postnatal rats

Effects of a non-competetive blocker of glutamate NMDA receptors, ketamine, on respiratory activity recorded from the phrenic nerve were studied in experiments on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of 3− to 4-day-old rats. The experiments were carried out under conditions where the ventrolateral medullary region (VLM) was left intact, or its rostral portion (projectionally corresponding to the chemosensitiveM zone) was separated by transection. Three-min-long application of 1.0 μM ketamine evoked a slight increase in the duration of inspiratory discharges (ID) and a statistically significant increase in their frequency. After the rostral VLM had been separated, similar ketamine application resulted in significant increases in the duration, amplitude, and integral intensity of ID and some drop in their frequency. An increase to 10 μM ketamine concentration in the superfusing solution determined a significant rise of the ID duration, which indicates the possibility of inhibition of the mechanisms switching inspiration to expiration. Concurrently, the ID frequency significantly dropped, while their amplitude and integral intensity increased. After separation of the rostral VLM, the latter ketamine concentration ceased to increase the ID duration, and their frequency and amplitude significantly dropped. Application of ketamine in the concentration of 100 μM resulted in rather profound decreases of all measured ID parameters, and separation of the rostral VLM exerted no influence on the direction of the above modifications. Thus, we obtained evidence of the involvement of NMDA receptors of the VLM in the control of temporal and frequency-amplitude parameters of respiratory activity of early postnatal rats. Possible localization of NMDA receptors and mechanisms of their involvement in inspiration-expiration switching and tonic inhibitory control of respiratory rhythms are discussed.     

Involvement of nitric oxide in realization of the NMDA influence on the respiratory rhythm generated by medullo-spinal preparations of early postnatal rats

The effects of blocking of NO synthase on the dynamics of NMDA-induced changes in the respiratory activity were studied in experiments on semi-isolatedin situ medullo-spinal preparations of 3- to 4-day-old rats. The experiments were carried out with the ventrolateral regions of the medulla (VLMR) left intact or when the rostral portion of this region (corresponding to the chemosensitive zoneM) had been separated by a transversial transection. Three-min-long application of 5.0 μM NMDA increased the frequency of inspiratory discharges (ID); the shifts were more intensive after separation of the VLM rostral portion. Superfusion of preparations with a solution containing 10.0 μM of an NO synthase inhibitor, methyl ester of N^G-nitro-L-arginine (MENA), increased the frequency and decreased the amplitude and integral intensity of ID generated by the preparations with the intact VLM, whereas after separation of the rostral VLM portion this inhibitor decreased the ID frequency. Application of 5 μM NMDA against the background of 10-min-long superfusion with the 10 μM MENA-containing solution resulted in no significant increase in the ID frequency. After the rostral VLM portion had been removed, NMDA application after superfusion with the MENA-containing solution led to frequency shifts which did not significantly differ from those in the absence of the blockade of NO synthase. Against the MENA influence, NMDA-induced depression of the ID amplitude became significantly more intensive. The experiments showed that during the early postnatal period endogenous NO is involved in realization of the NMDA influence on the parameters of respiratory activity of rats. Possible mechanisms of the influences exerted by activation of NMDA receptors and by the associated NO synthesis on regulation of the respiratory rhythmogenesis and their specificity within the early postnatal period are discussed.     

Pacemaker properties of respiratory neurons of the ventrolateral medullary regions in early postnatal rats

Spike activity of respiratory neurons of the ventrolateral medullary regions was studied under conditions of blocking of synaptic transmission. The experiments were carried out on superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of newborn (1st day of life) and 4- to 5-day-old rats. Part of the pre-inspiratory and (to a somewhat lesser extent) expiratory neurons of newborn rats appeared most resistive to superfusion of preparations with a low-Ca²⁺ (0.2 mM) and Mg²⁺-rich (5.0 mM) solution. Spike activity in some neurons of these groups was preserved up to 40 and 25 min, respectively, after mass inspiratory discharges in then. phrenicus had disappeared. Similar neurons in 4- to 5-day-old SIMSP were less resistive. Inspiratory neurons in animals of both age groups demonstrated no pacemaker properties. Coagulation of the regions where pre-inspiratory neurons are localized (the retrofacial zone) did not evoke irreversible blockade of respiratory rhythm in all SIMSP of 4- to-5-day-old rats and in most SIMSP of newborn animals. At the same time, coagulation of the zone where inspiratory neurons are concentrated (the pre-Bötzinger complex) resulted in the blockade of respiratory rhythm in all SIMSP, with no exceptions.Neirofiziologiya/Neurophysiology, Vol. 28, No. 6, pp. 273–284, November–December, 1996.     

Impact of NMDA Receptors and Nitric Oxide on pH Sensitivity of Medullary Mechanisms Controlling Respiratory Rhythm

We studied the dynamics of modifications of the respiratory activity generated by semi-isolated medullo-spinal preparations (SIMSP) of 3- to 4-day-old rats related to a drop in the pH of superfusing solution from 7.4 to 7.0. Reactions were recorded in the norm and under conditions of preliminary applications of a noncompetitive blocker of NMDA receptors, ketamine; an inhibitor of nitric oxide synthase (NOS), N^G-nitro-L-arginine methyl ester (L-NAME); a substrate for NO synthesis, L-arginine; or an exogenous NO donor, sodium nitroprusside (SN). Under control conditions, test applications of the solution with pH 7.0 resulted in a significant increase in the frequency of inspiratory discharges (ID) recorded from the phrenic nerve and drops in their amplitude and integral intensity. Such SIMSP extracellular acidification-induced responses were inhibited in a dose-dependent manner by ketamine and L-NAME (the effect of the latter was more intensive). The effects of agents increasing the NO level in the tissues were not uniform: L-arginine potentiated an increase in the ID frequency related to application of the acidified solution, while SN inhibited such a reaction. Our findings allow us to suppose that the stimulating influences of the pH-sensitive chemoreceptor structures of the ventrolateral medulla (VLM) on the activity of the medullary respiratory generator of early postnatal rats are realized with the involvement of NMDA receptors of excitatory amino acids and the process of enzyme-mediated NO production. It seems probable that endogenous synthesis of NO in VLM structures mediates and potentiates the effect of activation of the NMDA receptors on the medullary generator of the respiratory rhythm.     

Blocking of glutamate ionotropic receptors: Influence on the respiratory activity generated by medullo-spinal preparations of rats in hypoxia

We studied the influences of a non-competitive blocker of glutamate NMDA-receptors ketamune and of a competitive blocker of AMPA-kainate non-NMDA receptors, CNQX, on the respiratory activity generelated by superfusedin situ semi-isolated medullo-spinal preparations (SIMSP) of 3- to 4-day-old rats. We compared the ampes recorded under conditions of superfusion, a standard solution and the solution saturated with an anoxic isocapine gas mixture were compared; pO₂ in these solutions were 440±22 and 41±8 mm Hg, respectively. The experments were carried out with the ventrolateral medullary region (VLMR) left intact or after separation of its rostral part, which propertchonally corresponded to the chemosensitiveM zone. A 3-min-long hypoxic test initially evoked an increase in the frequency of inspiratory discharges (IR) in the phrenic nerve followed by a frequency drop within the final half of the test. After the rostral VLMR had been separated, the hypoxic test did not elicit a significant decrease in the IR frequency. After preliminary application of 1.0 or 10.0 μM ketamine or CNQX on intact preparations, the IR frequency under hypoxic conditions dropped within the first half of the test and increased in the second half, while the amplitude and integral intensity of these discharges were depressed more intensively than in hypoxia with no applications. Using ketamme and CNQX in the same concentrations resulted in significant drops in the amplitude, frequency, and integral intensity of IR recorde din the hypoxic test. Our experiments showed that in the early postnatal period glutamate ionotropic receptors of rostral VLMR neurons are involved in the control of IR frequency under hypoxic conditions. The possible role of glutamatergic control of the respiratory rhythm and mechanisms of the influences resulting from blocking of NMDA and non-NMDA receptors on the parameters of respiratory activity are discussed.     

Effects of modulation of cholinergic transmission of activity of the medullary respiratory generator of newborn rats:in vitro study

Periodic phasic activity (respiratory discharges) was recorded from the spinal ventral rootsC ₄−C ₅ in the experiments on isolated medullo-spinal preparations of 1- to 3-day-old rats. Applications of acetylcholine (ACh) in different concentrations and modifications of pH were tested under normal conditions and after treatment with cholinoblockers, atropine and benzohexonium, and an acetylcholinesterase blocker, physostigmine. ACh intensified periodic respiratory activity in a concentration-dependent manner, and the duration of postactivatory depression showed similar dependence. ACh-induced effects were facilitated after pH of the superfusing solution had been decreased. Atropine decreased the frequency of respiratory discharges and suppressed responses to ACh applications and pH modification. Contrastingly, benzohexonium and, especially, physostigmine in concentrations, exerting no significant independent influence on the frequency of respiratory activity, increased sensitivity of preparations and facilitated responses to ACh applications and pH decrease. Involvement of cholinergic neuronal mechanisms, localized in the chemosensitive region of the ventral surface of the medulla, in generation of periodic activity by the medullary respiratory generator is discussed.     

High pressure modifies respiratory activity in isolated rat brain stem-spinal cord

Exposure to hyperbaric pressure causes a constellation of motor disturbances and ventilatory difficulties in animals and humans. The present experiments were designed to examine the effects of hyperbaric pressure on the rhythmic activity of the respiratory center in the absence of peripheral sensory afferents by using the isolated brain stem-spinal cord preparation from newborn rats. In addition, we examined the effect of pressure on the response of the respiratory center to sensory input from the trigeminal and vagus cranial nerves. Hyperbaric pressure significantly depressed the mean inspiratory drive (frequency X time integral of single electrical bursts) in C5 but not in C1 ventral roots. Pressure also reduced the amount of inhibition on the respiratory activity normally exerted by trigeminal and vagal nerve stimulation and in some cases reversed it to excitation. It is concluded that in the absence of sensory input, exposure to hyperbaric pressure depresses central respiratory activity. However, in an intact system, it may alter the balance between excitation and inhibition and render the system hyperexcitable to the same sensory input.     

Adherence ofPasteurella multocida to porcine upper respiratory tract cells

A model to study the adherence ofPasteurella multocida to porcine upper respiratory tract cells is described. The ability of 27 differentP. multocida isolates to adhere to isolated tracheal epithelial cells was examined. The mean number of adherent bacterial cells was significantly greater (p<0.005) for capsular type A cells than for capsular type D cells. No significant differences were observed between toxigenic and nontoxigenic isolates, or between isolates exhibiting different somatic antigens. However, isolates from pigs without atrophic rhinitis showed only 65% of the adherence of isolates from pigs with atrophic rhinitis. Adherence ofP. multocida to porcine tracheal cells decreased with animal age; adherence to cells from adults was only half of the adherence to cells from newborn animals. The data indicate that, in the present experimental conditions, theP. multocida strains tested possess different abilities to attach to porcine upper respiratory tract cells.     

Synergism between cocaine and atropine at the caudal ventrolateral medulla of cats

We have previously reported that the anticholinergic properties of cocaine may be important in cocaine induced apneusis. We have studied the effects of the cholinergic muscarinic antagonist atropine (ATR) on cocaine induced apneusis at the caudal chemosensitive areas of the ventrolateral medulla oblongata (CVLM). Experiments were performed in urethane anesthetized and tracheotomized cats with the CVLM surgically exposed. Topical application of ATR (44 mM ) to the CVLM produced significant decrements in minute ventilation (V(E)) and mean arterial blood pressure (MABP) (P<0.05) but the effects on tidal volume (V(T)), respiratory frequency (f) and heart rate (HR) were not significant. Administration of cocaine (37 mM) to ATR pretreated animals increased the incidence of cocaine induced respiratory arrest to more than twofold greater than when cocaine was administered in the absence of pretreatment. The ATR pretreated animals that did not experience inspiratory arrest after cocaine were shown to exhibit significant decrements in f and V(E) as a consequence of prolonged inspiratory pauses. The reduction in MABP after cocaine in ATR pretreated animals was also significant. These results suggest that ATR enhances the central respiratory toxicity of cocaine by acting synergistically at CVLM chemosensitive sites.     

Influence of Candida albicans glycoprotein on 3-methylcholanthrene induced malignancy in newborn rodents

In the experimental conditions reportedCandida albicans glycoprotein has a stimulating effect on the course of 3-methylcholanthrene carcinogenesis in newborn rodents. Stimulation of 3-methylcholanthrene carcinogenesis in newborn rats was found following injections of 9.5 µg/g and 18.5 µg/g ofCandida albicans glycoprotein. Subcutaneous tumors occurred in the experimental animals earlier, with higher frequency and attained larger dimensions than in the control animals. Similar effects were observed in mice. In the experimental mice there was also a significantly higher number of thymomas. From the evidence presentedCandida albicans glycoprotein appears to act as a cocarcinogenic substance to 3-methylcholanthrene.This work was supported partially byDora Kaplan, Joan Sloan, Cathy Cooper Memorial Funds and the Leo Roon Foundation.     

Experimental infection withBasidiobolus haptosporus

The authors tried to reproduce experimentally theBasidiobolus haptosporus infection. Culture forms of the fungus were inoculated in 26 adult hamsters, in two newborn hamsters and in two marmosets. Oral, intratesticular, intrahepatic, intraperitonial and subcutaneous inoculations were made. Bethametasone was given prior to inoculation in a group of animals.The lesions produced were only of the foreign body type and there was no development of the fungus in the animal tissues. The AA concluded that an experimental model for theB. haptosporus infection has not yet been found.     

Modulation of dorsal horn neuronal activity by spinal cord stimulation in a rat model of neuropathy: The role of the dorsal funicles

We recorded the spike activity from spinal neurons In rats with a model of neuropathy after ligation of then. ishiadicus. A significantly increased frequency of background discharges and responsiveness to nonnoxious stimuli were observed in dorsal horn wide-dynamic range (convergent) neurons in a group of allodynic rats, as compared with non-allodynic and intact rats. Spinal cord stimulation (SCS) Induced a significant depression of both the principal responses and afterdischarges in allodynic rats. The frequency of background discharges was markedly decreased in approximately one third of the neurons. These effects outlasted SCS by about 10 rain. The moderating effect of SCS is considered a result of activation of distinctly different and complementary mechanisms: segmental and transsupraspinal. The former appears to be the most important in allodynic animals.     

Effects of neuromuscular blocking agents on central respiratory chemosensitivity in newborn rats

Neuromuscular blocking agents suppress central respiratory activity through their inhibitory effects on preinspiratory neurons and the synaptic drive from preinspiratory neurons to inspiratory neurons. Central CO2-chemosensitive areas, which partly consist of CO2-excited neurons, in the rostral ventrolateral medulla are thought to provide tonic drive to the central respiratory network and involve cholinergic mechanisms, which led us to hypothesize that neuromuscular blocking agents can inhibit CO2-excited neurons and attenuate respiratory CO2 responsiveness. To test this hypothesis, we used isolated brainstem-spinal cord preparations from newborn rats. The increase of C4 burst frequency induced by a hypercapnic superfusate, i.e. respiratory CO2 responsiveness, was suppressed by the application of neuromuscular blocking agents, either d-tubocurarine (10, 100 microM) or vecuronium (100 microM). These agents (40 microM) also induced hyperpolarization and decreases in firing frequency of CO2-excited neurons in the rostral ventrolateral medulla. Our results demonstrate that neuromuscular blocking agents inhibit CO2-excited tonic firing neurons and attenuate respiratory CO2 responsiveness.     

Expression of Ext1, Ext2, and heparanase genes in brain of senescence-accelerated OXYS rats in early ontogenesis and during development of neurodegenerative changes

Heparan sulfate (HS) and heparan sulfate proteoglycans (HSPG) play a significant role in brain development, and their structural and quantitative changes are revealed during aging and in neurodegenerative disorders. The mechanism of these changes is not clear, but is likely to be associated with alteration in the expression and/or activity of enzymes responsible for HSPG biosynthesis and degradation. The contents of mRNAs of the genes Ext1 and Ext2 encoding polymerization enzymes and of gene Hpse of heparanase degrading HS were determined in the brain of prematurely aging OXYS rats during early postnatal development and during appearance of signs of brain accelerated aging (at age of 1, 7, 14, 30, 60, and 420 days). Wistar rats of the same age were used as controls. Expression levels of the genes Ext1, Ext2, and Hpse in the brain of rats of both strains were maximal during the two first weeks of life, and the contents of mRNAs of all genes in the brain of newborn and 7-day-old OXYS rats were significantly higher than in Wistar rats. By the 14th day of life the differences leveled, but at the age of 30 days on the background of a decrease in the contents of mRNAs of Ext1, Ext2, and Hpse in OXYS rats they became more pronounced (three-, four-, and twofold, respectively). Differences between the strains were absent at the age of 60 days and 14 months, and expression of all the genes was significantly lower than in the newborn animals. A strong positive correlation was found between contents of mRNAs of all the studied genes, and this suggested that heparanase should be involved in HSPG metabolism together with Ext1 and Ext2. Based on these and earlier findings, we conclude that development of the OXYS rat brain occurs on the background of significant alterations in HSPG metabolism that precede the development of neurodegenerative manifestations recently detected by magnetic resonance imaging.     

Postnatal development of the Hering-Breuer reflex in the rat

The intensity of the Breuer-Hering inflation reflex was studied in newborn (1 day old), in young (8 days old) and in adult rats (90 days old) under urethane general anaesthesia (1.3 g/kg i.p.). The inflation pressure was adjusted with the aid of a water-valve. The reflex was present in all 3 age groups. An inflation pressure of 0.2 kPa applied in the course of expiration produced a long lasting apnoea in newborn rats which lasted 48 normal respiratory cycles. An inflation pressure of 0.5 kPa in young rats induced an apnoea lasting for only 3 normal respiratory cycles, whereas a pressure of 1 kPa in adult rats led to an apnoea which lasted for 20 normal respiratory cycles. The compliance of the respiratory system in relation to lung weight is approximately 5 times higher in adult rats compared with that of newborn rats. It is approximately double in comparison with young rats. The pressures of inflation mentioned in the 3 age categories can be considered as equieffective from the point of stimulation pulmonary stretch receptors. It can be concluded from these findings that the reflex of Breuer-Hering in newborn rats is more potent in comparison with adult rats, but it is lower in young rats at the age of 8 days. It is suggested that the differences observed are due to functional and anatomical maturation.     

Temperature and density-dependent effects of larval environment on Aedes aegypti competence for an alphavirus

Mosquito larvae experience multiple environmental stressors that may modify how subsequent adults interact with pathogens. We evaluated the effect of larval rearing temperature and intraspecific larval competition on adult mosquito immunity and vector competence for Sindbis virus (SINV). Aedes aegypti larvae were reared at two intraspecific densities (150 and 300 larvae) at 20° C and 30° C and the adults were fed artificially on citrated bovine blood containing 10(5) plaque forming units of SINV. Expression of cecropin, defensin, and transferrin was also evaluated in one- and five-day-old female adults. There was a direct relationship between larval density and SINV infection and dissemination rates at low temperature (20° C) and an inverse relationship between larval density and SINV infection rate at high temperature (30° C). Cecropin was only expressed in five-day-old adults that were raised at high temperature as larvae and was 20-fold over-expressed at low compared to high density treatments. Defensin and transferrin were under-expressed in one-day-old adults and over-expressed in five-day-old adults in all competition-temperature combinations relative to low density treatments at 20° C. These findings suggest that interaction between biotic and abiotic conditions of the larval environment may alter adult mosquito immunity resulting in enhanced vector competence for arboviruses.