Peripheral modulation of olfaction by physiological state in the Egyptian leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae)

Insects show behavioural plasticity based on their physiological state. Deprivation from a resource will normally make them more responsive to it or to perform behaviour increasing the probability of encountering such a resource. Modulation of the olfactory system has been shown mainly in the central nervous system, but also in the periphery. In this study, antennal sensitivity of females of the Egyptian cotton leaf worm Spodoptera littoralis to different plant and sex pheromone odours was measured using electroantennography (EAG). Different mating status, age, and feeding status were used to investigate peripheral changes in olfactory responses. Virgin females were found to be more sensitive to plant odours and sex pheromone compared to mated females. Age also had an impact on antennal sensitivity, 2 and 4 days old females being more sensitive than just-emerged ones. Such an increase in sensitivity could be explained by maturation of olfactory receptor neurons after emergence or by an increase in motivation as the available expected life time remaining decreases. Finally, feeding status did not modify the antennal sensitivity of females. A peripheral modulation could thus be demonstrated in the olfactory system of female Spodoptera littoralis at certain life stages.     

Mating‐Associated Changes in the Behaviour of Leptothorax gredleri Ant Queens

Throughout their lives, animals adapt their behaviour to environmental fluctuations and to their own requirements. In social insects, behavioural changes are often particularly conspicuous. For example, in many ant species, reproductive sexuals leave their maternal nests and engage in risky mating and dispersal activities. Female sexuals experience, during a short period of time, dramatic changes in terms of behaviour and environmental conditions. But because sexual activities of ants are not easily observed, few studies have quantified in detail how behaviour alters with maturation and mating. We studied how various behavioural traits of Leptothorax gredleri female sexuals, a species in which female sexuals attract males by ‘female calling’, change before and after mating. We tested the hypothesis that behavioural variation reflects the altered requirements of queens to adapt to a particular situation. To this end, we compared geotactic, phototactic and locomotor behaviour across a wide range of life stages from lightly coloured, unmated female sexuals to old, mated queens. The results showed that female sexuals of L. gredleri change conspicuously their geotactic, phototactic and locomotor behavioural traits over their life stages. Three different behavioural states were evident (1) from light to dark female sexuals, individuals have negative phototaxis and reduced locomotor activity; (2) mature female sexuals during the daily period of sexual activity have strong phototaxis, negative geotaxis and an important locomotor activity; and (3) freshly mated and old mated queens avoid light and decrease their locomotor activity. These sharp differences in behaviour between stages match the transition from the relative safety of the nest chamber to the adversary world outside the nest , and back.     

The sensitivity of the labellar sugar receptors of Phormia regina in relation to feeding

The hypothesis that behavioural feeding threshold of P. regina modulates and is modulated by the sensitivity of the labellar contact chemoreceptors is not supported by the examination of individual flies.Sensitivity (number of impulses fired in the first second of stimulation) of the sugar receptors in selected labellar hairs of flies of known age was recorded periodically on a fixed schedule for up to 72 hr. Experimental flies were hand fed 2.0 M fructose once every 24 hr. No correlations between feeding or age and receptor sensitivity were found. Statistically significant changes in firing frequency did occur but were unrelated to feeding and age.The proboscis extension response, on which behavioural threshold measures are based, is known to be triggered by the first few sugar receptor spikes of sufficient frequency. Neither age nor feeding significantly affected the number or frequency of impulses during the first 50 msec of stimulation.     

Postnatal differential expression of chemoreceptors of free fatty acids along the gastrointestinal tract of supplemental feeding v. grazing kid goats

The gastrointestinal tract (GIT) of animals is capable of sensing various kinds of nutrients via G-protein coupled receptor-mediated signaling transduction pathways, and the process is known as ‘gut nutrient chemosensing’. GPR40, GPR41, GPR43 and GPR119 are chemoreceptors for free fatty acids (FFAs) and lipid derivatives, but they are not well studied in small ruminants. The objective of this study is to determine the expression of GPR40, GPR41, GPR43 and GPR119 along the GIT of kid goats under supplemental feeding (S) v. grazing (G) during early development. In total, 44 kid goats (initial weight 1.35±0.12 kg) were slaughtered for sampling (rumen, abomasum, duodenum, jejunum, ileum, cecum, colon and rectum) between days 0 and 70. The expression of GPR41 and GPR43 were measured at both mRNA and protein levels, whereas GPR40 and GPR119 were assayed at protein level only. The effects of age and feeding system on their expression were variable depending upon GIT segments, chemoreceptors and expression level (mRNA or protein), and sometimes feeding system × age interactions (P<0.05) were observed. Supplemental feeding enhanced expression of GPR40, GPR41 and GPR43 in most segments of the GIT of goats, whereas G enhanced expression of GPR119. GPR41 and GPR43 were mainly expressed in rumen, abomasum and cecum, with different responses to age and feeding system. GPR41 and GPR43 expression in abomasum at mRNA level was greatly (P<0.01) affected by both age and feeding system; whereas their expression in rumen and abomasum at protein level were different, feeding system greatly (P<0.05) affected GPR41 expression, but had no effect (P>0.05) on GPR43 expression; and there were no feeding system×age interactions (P>0.05) on GPR41 and GPR43 protein expression. The expression of GPR41 and GPR43 in rumen and abomasum linearly (P<0.01) increased with increasing age (from days 0 to 70). Meanwhile, age was the main factor affecting GPR40 expression throughout the GIT. These outcomes indicate that age and feeding system are the two factors affecting chemoreceptors for FFAs and lipid derivatives expression in the GIT of kids goats, and S enhanced the expression of chemoreceptors for FFAs, whereas G gave rise to greater expression of chemoreceptors for lipid derivatives. Our results suggest that enhanced expression of chemoreceptors for FFAs might be one of the benefits of early supplemental feeding offered to young ruminants during early development.     

Low pasture allowance until late gestation in ewes: behavioural and physiological changes in ewes and lambs from lambing to weaning

Low pasture allowance during gestation affects ewes’ BW at parturition, the bond with their lamb, lamb development, and thus also may affect their responses to weaning. The objectives were to determine if native pasture allowance from before conception until late pregnancy affects ewe–lamb behaviours at lambing, ewes’ milk yield, lambs’ BW, and the behavioural and physiological changes of ewes and lambs at weaning. From 23 days before conception until 122 days of pregnancy, 24 ewes grazed on two different native pasture allowances: high (10 to 12 kg of dry matter (DM)/100 kg of BW per day; HPA treatment; n=12) or low (5 to 8 kg of DM/100 kg of BW per day; LPA treatment; n=12). Thereafter, all ewes grazed on Festuca arundinacea and received rice bran and crude glycerine. Ewes’ body condition score (BCS) and BW were recorded during pregnancy and postpartum periods. Milk yield was determined on days 32, 41 and 54 after lambing. Lambs’ BW was recorded from birth until 72 days after lambing. Latency from parturition until the ewe licked her lamb, maternal behaviour score (a test that evaluates maternal attachment to the lamb) and latency for lamb to stand up and suckle were determined. The behaviour of the lambs and ewes was recorded before and after weaning (at 65 days). The ewes’ serum total protein, albumin and globulin concentrations were measured before and after weaning. The HPA ewes presented greater BW (P<0.005) and BCS (P<0.005) than the LPA ewes during pregnancy and postpartum (P<0.04), and had a greater milk yield than the LPA ewes (P<0.03). Treatments did not influence any behaviour at lambing, lambs’ BW, neither the ewes’ behavioural and physiological changes at weaning. HPA lambs paced and vocalized more than LPA lambs (P<0.0001). The variation of albumin concentration before and after weaning was greater in the HPA lambs than in the LPA lambs (P<0.0001). In conclusion, although ewes’ BW, BCS and milk production were affected by pasture allowance until late pregnancy, this did not affect the behaviours that lead to the establishment of the mother–young bond, nor the ewes’ behavioural responses at weaning. Lambs reared by ewes that grazed on low pasture allowance during pregnancy presented fewer behavioural changes and a lower decrease of albumin concentration after weaning. Lambs’ BW was not affected by the feeding received by their mothers.     

Rôle of gustation and olfaction in food plant discrimination in the tobacco hornworm, Manduca sexta

The rôle of the various chemoreceptors in behavioural discrimination among closely related food plants was studied in Manduca sexta larvae. Amputation of the three types of receptors in various combinations showed that: (1) removal of the maxillary styloconica (gustatory) causes a drastic loss of discrimination; (2) ablation of either the maxillary palpi or antennae (olfactory) also reduces discrimination, but to a lesser degree; and (3) amputation of both palpi and antennae simultaneously causes a severe discriminatory loss comparable to that of gustatory loss. We conclude that both gustation and olfaction are important for host plant discrimination. These chemosensory organs were also shown to play a strong role in the induction of preference. Unilateral extirpations of all three sense organs caused no detectable loss, demonstrating their redundancy in normal animals.     

Behavioural phenotypes over the lifetime of a holometabolous insect

Introduction: Behavioural traits can differ considerably between individuals, and such differences were found to be consistent over the lifetime of an organism in several species. Whether behavioural traits of holometabolous insects, which undergo a metamorphosis, are consistent across ontogeny is virtually unexplored. We investigated several behavioural parameters at five different time points in the lifetime of the holometabolous mustard leaf beetle Phaedon cochleariae (Coleoptera: Chrysomelidae), two times in the larval (second and third larval stage) and three times in the adult stage. We investigated 1) the stability of the behavioural phenotype (population level), 2) whether individuals rank consistently across behavioural traits and over their lifetime (individual level), and 3) in how far behavioural traits are correlated with the developmental time of the individuals.Results: We identified two behavioural dimensions in every life stage of P. cochleariae, activity and boldness (population level). Larvae and young adults ranked consistently across the investigated behavioural traits, whereas consistency over time was only found in adults but not between larvae and adults (individual level). Compared to adult beetles, larvae were less active. Moreover, younger larvae were bolder than all subsequent life stages. Over the adult lifetime of the beetles, males were less active than females. Furthermore, the activity of second instar larvae was significantly negatively correlated with the development time.Conclusions: Our study highlights that, although there is no individual consistency over the larval and the adult life stage, the behavioural clustering shows similar patterns at all tested life stages of a holometabolous insect. Nevertheless, age- and sex-specific differences in behavioural traits occur which may be explained by different challenges an individual faces at each life stage. These differences are presumably related to the tremendous changes in life-history traits from larvae to adults and/or to a niche shift after metamorphosis as well as to different needs of both sexes, respectively. A faster development of more active compared to less active second instar larvae is in line with the pace-of-life syndrome. Overall, this study demonstrates a pronounced individuality in behavioural phenotypes and presumably adaptive changes related to life stage and sex.     

Functional Organization of a Multimodular Bacterial Chemosensory Apparatus

Chemosensory systems (CSS) are complex regulatory pathways capable of perceiving external signals and translating them into different cellular behaviors such as motility and development. In the δ-proteobacterium Myxococcus xanthus, chemosensing allows groups of cells to orient themselves and aggregate into specialized multicellular biofilms termed fruiting bodies. M. xanthus contains eight predicted CSS and 21 chemoreceptors. In this work, we systematically deleted genes encoding components of each CSS and chemoreceptors and determined their effects on M. xanthus social behaviors. Then, to understand how the 21 chemoreceptors are distributed among the eight CSS, we examined their phylogenetic distribution, genomic organization and subcellular localization. We found that, in vivo, receptors belonging to the same phylogenetic group colocalize and interact with CSS components of the respective phylogenetic group. Finally, we identified a large chemosensory module formed by three interconnected CSS and multiple chemoreceptors and showed that complex behaviors such as cell group motility and biofilm formation require regulatory apparatus composed of multiple interconnected Che-like systems.     

Environmental enrichment promotes neural plasticity and cognitive ability in fish

Different kinds of experience during early life can play a significant role in the development of an animal''s behavioural phenotype. In natural contexts, this influences behaviours from anti-predator responses to navigation abilities. By contrast, for animals reared in captive environments, the homogeneous nature of their experience tends to reduce behavioural flexibility. Studies with cage-reared rodents indicate that captivity often compromises neural development and neural plasticity. Such neural and behavioural deficits can be problematic if captive-bred animals are being reared with the intention of releasing them as part of a conservation strategy. Over the last decade, there has been growing interest in the use of environmental enrichment to promote behavioural flexibility in animals that are bred for release. Here, we describe the positive effects of environmental enrichment on neural plasticity and cognition in juvenile Atlantic salmon (Salmo salar). Exposing fish to enriched conditions upregulated the forebrain expression of NeuroD1 mRNA and improved learning ability assessed in a spatial task. The addition of enrichment to the captive environment thus promotes neural and behavioural changes that are likely to promote behavioural flexibility and improve post-release survival.     

Denervation of peripheral chemoreceptors decreases breathing movements in fetal sheep

The role of the peripheral chemoreceptors in the control of fetal breathing movements has not been fully defined. To determine whether denervation of the peripheral chemoreceptors affects fetal breathing movements, we studied 14 chronically catheterized fetal sheep from 120 to 138 days of gestation. In seven fetuses the chemoreceptors were denervated by bilateral section of the vagus and carotid sinus nerves; in seven others, sham operations were performed. We compared several variables during two study periods: 0-5 and 6-13 days after operation. In the denervated fetuses there were significant decreases in the incidence and amplitude of fetal breathing movements during both study periods. There were no differences between the two groups in incidence of low-voltage electrocortical activity, arterial pH and blood gas tensions, fetal heart rate, mean arterial blood pressure, or duration of survival after operation or birth weight. We conclude that denervation of the peripheral chemoreceptors decreases fetal breathing movements. These results indicate that the peripheral chemoreceptors are active during fetal life and participate in the control of fetal breathing movements.     

Internal Sense of Direction: Sensing and Signaling from Cytoplasmic Chemoreceptors

SUMMARY

Chemoreceptors sense environmental signals and drive chemotactic responses in Bacteria and Archaea. There are two main classes of chemoreceptors: integral inner membrane and soluble cytoplasmic proteins. The latter were identified more recently than integral membrane chemoreceptors and have been studied much less thoroughly. These cytoplasmic chemoreceptors are the subject of this review. Our analysis determined that 14% of bacterial and 43% of archaeal chemoreceptors are cytoplasmic, based on currently sequenced genomes. Cytoplasmic chemoreceptors appear to share the same key structural features as integral membrane chemoreceptors, including the formations of homodimers, trimers of dimers, and 12-nm hexagonal arrays within the cell. Cytoplasmic chemoreceptors exhibit varied subcellular locations, with some localizing to the poles and others appearing both cytoplasmic and polar. Some cytoplasmic chemoreceptors adopt more exotic locations, including the formations of exclusively internal clusters or moving dynamic clusters that coalesce at points of contact with other cells. Cytoplasmic chemoreceptors presumably sense signals within the cytoplasm and bear diverse signal input domains that are mostly N terminal to the domain that defines chemoreceptors, the so-called MA domain. Similar to the case for transmembrane receptors, our analysis suggests that the most common signal input domain is the PAS (Per-Arnt-Sim) domain, but a variety of other N-terminal domains exist. It is also common, however, for cytoplasmic chemoreceptors to have C-terminal domains that may function for signal input. The most common of these is the recently identified chemoreceptor zinc binding (CZB) domain, found in 8% of all cytoplasmic chemoreceptors. The widespread nature and diverse signal input domains suggest that these chemoreceptors can monitor a variety of cytoplasmically based signals, most of which remain to be determined.     

Relative latency of responses of chemoreceptor afferents from aortic and carotid bodies

Discharges from aortic and carotid body chemoreceptor afferents were simultaneously recorded in 18 anesthetized cats to test the hypothesis that aortic chemoreceptors, because of their proximity to the heart, respond to changes in arterial blood gases before carotid chemoreceptors. We found that carotid chemoreceptor responses to the onset of hypoxia and hypercapnia, and to the intravenously administered excitatory drugs (cyanide, nicotine, and doxapram), preceded those of aortic chemoreceptors. Postulating that this unexpected result was due to differences in microcirculation and mass transport, we also investigated their relative speed of responses to changes in arterial blood pressure. The aortic chemoreceptors responded to decreases in arterial blood pressure before the carotid chemoreceptors, supporting the idea that the aortic body has microcirculatory impediments not generally present in the carotid body. These findings strengthened the concept that carotid bodies are more suited for monitoring blood gas changes due to respiration, whereas aortic bodies are for monitoring circulation.     

Comparative toxicity of phosphine to developmental stages of three Callosobruchus species infesting stored pulses

Bruchids pose serious threat to stored pulses, and their successful management largely depends on phosphine fumigation. For the first time, the comparative assessment of phosphine toxicity to all the developmental stages of three bruchid species in India was attempted at varied concentrations and exposure times. Based on probit estimates, the egg stages found to be least sensitive to phosphine followed by pupae and larvae, whereas adults were highly sensitive. Among the age groups of eggs, the early age groups (0–2 days old) were less sensitive than later stages (3–6 days old). The bruchid species viz., Callosobruchus maculatus (F.), C. analis (F.), and C. chinensis L. exhibited a variable degree of susceptibility irrespective of life stages and exposure periods tested. However, the collective probit estimates indicated C. maculatus being slightly less sensitive followed by C. analis and C. chinensis. Except in 0–2 day old eggs, the mortality response in 3–6 day old eggs, larvae, pupae, and adults was increased with increasing phospine concentrations and exposure period. The mortality response got even steeper at 48 and 72 h exposures as evident by decreasing LC50 and LC90 values. The information generated on phospine sensitivity in different life stages would serve as baseline data to design insecticide resistance studies in future and also to ascertain stage-specific Concentration vs. time (Ct) products for the recommendation of phosphine doses for successful management of bruchids during any of their life stages under storage conditions.     

Temporal modulation and adaptive control of the behavioural response to odours in Rhodnius prolixus

It has been demonstrated in several insect species that a circadian clock makes the whole of antennal chemoreceptors more sensitive during a particular temporal window every day. This assessment raises the question about how insects exhibiting bimodal activity handle their sensitivity to odours which are relevant at different moments of the day. To shed some light on this problem, we studied in Rhodnius prolixus the daily dynamics of their responsiveness to CO₂ (host-associated cue) and aggregation cues (refuge-associated), which are relevant at dusk and dawn, respectively. We analysed: (1) whether a temporal modulation of the responsiveness to odours does exist in R. prolixus, (2) if this modulation is a general one or it is specific for each type of volatile, and (3) if it is controlled by exogenous or endogenous mechanisms. We found that the responsiveness to CO₂ only occurs at dusk and that to assembling odours is restricted to dawn. Experiments under free-running conditions revealed that only the responsiveness to CO₂ is controlled by a circadian clock, but not that to assembling signals. Thus, by combining endogenous and exogenous mechanisms, sensitivities to different odours are adjusted according to their associated behavioural context and moment of the day.     

Song discrimination by nestling collared flycatchers during early development

Pre-zygotic isolation is often maintained by species-specific signals and preferences. However, in species where signals are learnt, as in songbirds, learning errors can lead to costly hybridization. Song discrimination expressed during early developmental stages may ensure selective learning later in life but can be difficult to demonstrate before behavioural responses are obvious. Here, we use a novel method, measuring changes in metabolic rate, to detect song perception and discrimination in collared flycatcher embryos and nestlings. We found that nestlings as early as 7 days old respond to song with increased metabolic rate, and, by 9 days old, have increased metabolic rate when listening to conspecific when compared with heterospecific song. This early discrimination between songs probably leads to fewer heterospecific matings, and thus higher fitness of collared flycatchers living in sympatry with closely related species.     

Behavioural alterations are independent of sickness behaviour in chronic experimental Chagas disease

The existence of the nervous form of Chagas disease is a matter of discussion since Carlos Chagas described neurological disorders, learning and behavioural alterations in Trypanosoma cruzi-infected individuals. In most patients, the clinical manifestations of the acute phase, including neurological abnormalities, resolve spontaneously without apparent consequence in the chronic phase of infection. However, chronic Chagas disease patients have behavioural changes such as psychomotor alterations, attention and memory deficits, and depression. In the present study, we tested whether or not behavioural alterations are reproducible in experimental models. We show that C57BL/6 mice chronically infected with the Colombian strain of T. cruzi (150 days post-infection) exhibit behavioural changes as (i) depression in the tail suspension and forced swim tests, (ii) anxiety analysed by elevated plus maze and open field test sand and (iii) motor coordination in the rotarod test. These alterations are neither associated with neuromuscular disorders assessed by the grip strength test nor with sickness behaviour analysed by temperature variation sand weight loss. Therefore, chronically T. cruzi-infected mice replicate behavioural alterations (depression and anxiety) detected in Chagas disease patients opening an opportunity to study the interconnection and the physiopathology of these two biological processes in an infectious scenario.     

Northward range expansion requires synchronization of both overwintering behaviour and physiology with photoperiod in the invasive Colorado potato beetle (Leptinotarsa decemlineata)

Photoperiodic phenological adaptations are prevalent in many organisms living in seasonal environments. As both photoperiod and growth season length change with latitude, species undergoing latitudinal range expansion often need to synchronize their life cycle with a changing photoperiod and growth season length. Since adaptive synchronization often involves a large number of time-consuming genetic changes, behavioural plasticity might be a faster way to adjust to novel conditions. We compared behavioural and physiological traits in overwintering (diapause) preparation in three latitudinally different European Colorado potato beetle (Leptinotarsa decemlineata) populations reared under two photoperiods. Our aim was to study whether behavioural plasticity could play a role in rapid range expansion into seasonal environments. Our results show that while burrowing into the soil occurred in the southernmost studied population also under a non-diapause-inducing long photoperiod, the storage lipid content of these beetles was very low compared to the northern populations. However, similar behavioural plasticity was not found in the northern populations. Furthermore, the strongest suppression of energy metabolism was seen in pre-diapause beetles from the northernmost population. These results could indicate accelerated diapause preparation and possibly energetic adjustments due to temporal constraints imposed by a shorter, northern, growth season. Our results indicate that behavioural plasticity in burrowing may have facilitated initial range expansion of L. decemlineata in Europe. However, long-term persistence at high latitudes has required synchronization of burrowing behaviour with physiological traits. The results underline that eco-physiological life-history traits of insects, such as diapause, should be included in studies on range expansion.     

Timing of the water-to-land transition and metamorphosis in the land hermit crab Coenobita compressus H. Milne Edwards: evidence that settlement and metamorphosis are de-coupled

After metamorphosing from the last larval stage to the transitional megalopal stage in the marine plankton, the hermit crab Coenobita compressus moves ashore where it undergoes a second metamorphosis to the first juvenile instar on land. In two experiments using laboratory-reared crabs, I moved megalopae from water to land after different amounts of time at this stage and investigated the impact of this manipulation on the timing of and survival through the second metamorphosis. In the Involuntary Settlement experiment, megalopae were moved to land when they were 3, 6, 9, 12, or 15 days old. None of those moved between the ages of 3 and 6 days survived through metamorphosis, but the majority of 9-day-old megalopae survived, as did most 12- and 15-day-old megalopae. This suggests that developmental changes early in the megalopal stage prepare C. compressus for terrestrial life. Once on land, megalopae that had been moved to land at 9 days spent about nine additional days there before metamorphosing, while 12- and 15-day-old megalopae metamorphosed after spending about 5 and 4 days, respectively, on land. In the Voluntary Settlement experiment, megalopae were given access to land when they were 1, 5, 10, or 15 days old, but were not forced to make the transition. Those given access to land after 1 day voluntarily left their dishes for the first time after an average of 7 days in water. Those given access when they were 5 days old remained in water about 4 days longer, while those given access when they were 10 and 15 days old left after less than a day. In both experiments, the timing of metamorphosis relative to settlement (i.e., transition to land) showed that these events are dissociated to a degree and revealed the presence of a metamorphic clock. I discuss why the dissociation of settlement and metamorphosis may have been favored in the land hermit crab and in another anomuran crab.     

Maternal telomere length inheritance in the king penguin

Telomeres are emerging as a biomarker for ageing and survival, and are likely important in shaping life-history trade-offs. In particular, telomere length with which one starts in life has been linked to lifelong survival, suggesting that early telomere dynamics are somehow related to life-history trajectories. This result highlights the importance of determining the extent to which telomere length is inherited, as a crucial factor determining early life telomere length. Given the scarcity of species for which telomere length inheritance has been studied, it is pressing to assess the generality of telomere length inheritance patterns. Further, information on how this pattern changes over the course of growth in individuals living under natural conditions should provide some insight on the extent to which environmental constraints also shape telomere dynamics. To fill this gap partly, we followed telomere inheritance in a population of king penguins (Aptenodytes patagonicus). We tested for paternal and maternal influence on chick initial telomere length (10 days old after hatching), and how these relationships changed with chick age (at 70, 200 and 300 days old). Based on a correlative approach, offspring telomere length was positively associated with maternal telomere length early in life (at 10 days old). However, this relationship was not significant at older ages. These data suggest that telomere length in birds is maternally inherited. Nonetheless, the influence of environmental conditions during growth remained an important factor shaping telomere length, as the maternal link disappeared with chicks'' age.     

Identification of a subsurface area in the ventral medulla sensitive to local changes in PCO2.

The exact location of the central respiratory chemoreceptors sensitive to changes in PCO2 has not yet been determined. To avoid the confounding effects of the cerebral circulation, we used the in vitro brain stem-spinal cord of neonatal rats (1-5 days old) to identify areas within 500 microns of the ventral surface of the medulla where changes in PCO2 evoked a sudden increase in the rate of respiratory neural activity. The preparation was superfused with mock cerebrospinal fluid (CSF) while maintained at constant temperature (26 +/- 1 degrees C) and pH (7.34). Respiratory frequency increased linearly with decreases in superfusate pH (r2 = 0.92, P less than 0.001), indicating that the respiratory circuitry for the detection of CO2 and stimulation of breathing was intact in this preparation. The search for central chemoreceptors was performed with a specially designed micropipette that allowed microejection of 2-10 nl of mock CSF equilibrated with different CO2-O2 gas mixtures. The pipette was advanced in 50- to 100-microns steps by use of a microdrive to a maximum depth of 500 microns from the surface of the ventral medulla. Depending on the location of the micropipette, ejection of CO2-acidified mock CSF at depths of 100-350 microns below the ventral surface of the medulla stimulated neural respiratory output. Using this response as an indication of the location of central respiratory chemoreceptors, we found that chemoreceptive elements were located in a column in the ventromedial medulla extending from the hypoglossal rootlets caudally to an area 0.75 mm caudal to VI nerve in the rostral medulla.(ABSTRACT TRUNCATED AT 250 WORDS)