Muscle chemoreflex alters carotid sinus baroreflex response in humans

Papelier, Y., P. Escourrou, F. Helloco, and L. B. Rowell.Muscle chemoreflex alters carotid sinus baroreflex response inhumans. J. Appl. Physiol. 82(2):577-583, 1997.The arterial baroreflex opposes pressor responsesto muscle ischemia (muscle chemoreflex). Our experiments sought toquantify the unknown effects of muscle chemoreflex on carotid sinusbaroreflex (CSB) sensitivity. We generated CSB stimulus-response (S-R)curves by pulsatile application (triggered by each electrocardiogram Rwave) of positive and negative neck pressure (from 60 to 80 mmHgin 20-mmHg steps of 20 s each) in seven normal young men. S-R curveswere obtained at rest (upright), during the last 3 min of upright cycleergometer exercise (150 W), and at the first minute of postexerciserecovery with leg circulation free (control). A second study repeatedthe same procedures, except that leg circulation was occluded 20 sbefore the end of exercise to elicit muscle chemoreflex, and occlusionwas maintained during recovery measurements (~3- to 4-min duration).S-R curves for CSB were shifted upward and rightward (25 mmHg) tohigher arterial blood pressure (BP) by exercise and less so (10 mmHg) in recovery (free leg flow). Postexercise occlusion (musclechemoreflex) raised BP and shifted S-R curves above exercise curves.CSB gain rose from 0.26 ± 0.06 (control) to 0.44 ± 0.08 (occlusion) during positive neck pressure application andwas reduced from 0.14 ± 0.04 to zero (0.04 ± 0.03) during negative neck pressure. Heart rate responses duringpostexercise muscle chemoreflex were not significantly different fromcontrol. Results reveal a nonlinear summation of CSB and musclechemoreflex effects on BP. BP-raising capability of muscle chemoreflexenhances CSB responses to hypotension but overpowers baroreflexopposition to hypertension.

     

The sequence,organization, and evolution of the Locusta migratoria mitochondrial genome

The sequencing of the cloned Locusta migratoria mitochondrial genome has been completed. The sequence is 15,722 by in length and contains 75.3% A+T, the lowest value in any of the five insect mitochondrial sequences so far determined. The protein coding genes have a similar A+T content (74.1%) but are distinguished by a high cytosine content at the third codon position. The gene content and organization are the same as in Drosophila yakuba except for a rearrangement of the two tRNA genes tRNA^lys and tRNA^asp. The A+T-rich region has a lower A+T nucleotide content than in other insects, and this is largely due to the presence of two G+C-rich 155-bp repetitive sequences at the 5 end of this section and the beginning of the adjacent small rRNA gene. The sizes of the large and small rRNA genes are 1,314 and 827 bp, respectively, and both sequences can be folded to form secondary structures similar to those previously predicted for Drosophila. The tRNA genes have also been modeled and these show a strong resemblance to the dipteran tRNAs, all anticodons apparently being conserved between the two species. A comparison of the protein coding nucleotide sequences of the locust DNA with the homologous sequences of five other arthropods (Drosophila yakuba, Anopheles quadrimaculatus, Anopheles gambiae, Apis mellifera, and Artemia franciscana) was performed. The amino acid composition of the encoded proteins in Locusta is similar to that of Drosophila, with a Dayhoff distance twice that of the distance between the fruit fly and the mosquitoes. A phylogenetic analysis revealed the locust genes to be more similar to those of the Dipterans than to those of the honeybee at both the nucleotide and amino acid levels. A comparative analysis of tRNA orders, using crustacean mtDNAs as outgroups, supported this. This high level of divergence in the Apis genome has been noted elsewhere and is possibly an effect of directional mutation pressure having resulted in an accelerated pattern of sequence evolution. If the general assumption that the Holometabola are monophyletic holds, then these results emphasize the difficulties of reconstructing phylogenies that include lineages with variable substitution rates and base composition biases. The need to exercise caution in using information about tRNA gene orders in phylogenetic analysis is also illustrated. However, if the honeybee sequence is excluded, the correspondence between the other five arthropod sequences supports the findings of previous studies which have endorsed the use of mtDNA sequences for studies of phylogeny at deep levels of taxonomy when mutation rates are equivalent. Correspondence to: P.K. Flook     

Experiments on aggregations of Phymateus purpurascens (Orthoptera, Acrididae, Pyrgomorphinae)

Phymateus purpurascens Karsch has been studied in the wild and in captivity in Uganda. Its habits, colouration, behaviour and life cycle are described.
All individuals are attracted towards each other by visual stimuli, and a moving individual is more attractive than a stationary one. This behaviour is unchanged by several instars in isolation. The aggregated larvae tend to move in synchronous bursts. and it is suggested that this is due to retinal image stabilization by an optomotor reflex.
In an open field all instars are attracted towards isolated vertical objects in the visual field. This, together with the interindividual visual responses described, produces columns of moving insects. No olfactory communication could be demonstrated.
Adults and larvae behave similarly in experimental situations; this contrasts with the observed dispersion in the wild with increasing age. It is suggested that dispersion results from loss of visual contact, caused by (a) loss of the conspicuous larval colouration, (b) chance isolation, and (c) increased mobility of fledged adults. The possible biological function of the gregariou habit is discussed, and the significance of the various colour patterns of the life history as inter-and intraspecific signals.     

Birth intervals ofCercopithecus monkeys of the kakamega forest,Kenya

Data on interbirth intervals are reported for two forest-living guenons,Cercopithecus mitis andC. ascanius, from a western Kenyan site. Measured intervals for females whose first offspring survived varied from 24 to 54 months (median 47,N=10) forC. mitis, and from 49 to 60 months (median 52,N=3) forC. ascanius. Intervals were shorter when the first of two offspring died. These results are supported by data on estimated intervals, in which the date of the first of two births was estimated, and incomplete intervals. Our measurements exceed previous estimates of interbirth intervals in wild populations and measured intervals of captive animals. Compared to closely related species inhabiting unpredictable and seasonal environments, these forest guenons breed very slowly indeed.     

Three descending interneurons reporting deviation from course in the locust

Three descending brain interneurons (DNI, DNM, DNC) are described from Locusta migratoria. All are paired, dorsally situated neurons, with soma in the protocerebrum, input dendrites in the proto- and deuterocerebrum, and a single axon running to the metathoracic ganglion and sometimes further. In DNI the soma and all cerebral arborizations lie ipsilateral to the axon. Discrete regions of arborization lie in the ipsilateral and medial ocellar tracts, the midprotocerebrum and the deuterocerebrum. In the other ganglia the axon branches only ipsilaterally, principally laterally in the flight motor neuropil but also towards the midline. DNC is similarly organized to DNI, but the cell crosses the midline in the brain. Soma, the single projection into a lateral ocellar tract, and the midprotocerebral arborization all lie contralateral to the axon. The deuterocerebral arborization is, however, ipsilateral to the axon. The pattern of projections in the remaining ganglia resembles that of DNI. The soma and all cerebral arborizations of DNM lie ipsilateral to the axon. The arborization is only weakly subdivided into protocerebral, deuterocerebral and medial ocellar tract regions. In the remaining ganglia the arborization extends bilaterally to similar areas of both left and right flight motor neuropil. A table of synonymy is given, equating the various names used for these neurons by previous authors. The morphology correlates well with the known input and output connections. They respond physiologically to deviations from the normal flight posture mediated by ocelli, eyes and wind hairs and connect to the thoracic flight apparatus.     

Three descending interneurons reporting deviation from course in the locust

The DNI, DNM and DNC descending interneurons all have very similar properties and are each at the convergence of visual, ocellar, wind-hair and other mechanoreceptor inputs. The 3 neurons respond almost exclusively to movement of the animal in space about its three axes of rotation. All are spatially and directionally selective. Movements in the preferred sense produce increasingly strong responses with amplitude and absolute position, while movements in the antipreferred sense usually elicit no response at all. Movements in the preferred sense, but towards, rather than away from, the normal flying position start to produce responses only as the animal approaches the normal flight position. The neurons function as feature detectors, responding only to specific sorts of deviation from course. DNI, DNM and DNC differ from one another principally in their directionality. DNI responds optimally to a diving banked turn to the ipsilateral side, DNM to downwards pitch, and the DNC to a diving banked turn to the contralateral side. The DN neurons contribute to the production of steering manoeuvres. They appear to be representatives of a larger class of descending interneurons bringing exteroceptive sensory input to the thoracic locomotory neuropil. The occurrence of this class of units in locusts and other insects is discussed.     

Sexual dimorphism and mating systems: jumping to conclusions

Previous studies have suggested that there is a strong relationship between a high degree of aggressive competition among males for access to fertile females and large body and canine size in males. It has further been suggested that such a relationship among living primates can be used to infer the social organization of extinct primate species from the degree of sexual dimorphism exhibited. Our field studies of patas (Erythrocebus patas) and blue monkeys (Cercopithecus mitis), two species which had previously been characterized as having one-male ‘harem’ group structures, indicate considerable variability in mating systems. We suggest, on the basis of our observations of these species, that factors other than male-male competition (e.g., predation) may also have influenced the degree of dimorphism in primates.