[Influence of precocene II on the sensory system of antennae and mouthparts in larvae of the fruit tree tortricid Archips podana Scop. (Lepidoptera: Tortricidae)].

The influence of precocene II, an antijuvenile agent, on morphological characters of the chemoreceptor apparatus of antennae and mouthparts was studied in fifth instar A. podana larvae. Treatment with different doses of precocene was performed at the egg stage. It proved to cause changes in the form and number of basiconic sensilla on the maxillary palps and galea and in the size of basiconic sensilla on the second and third antennal segments. The results are discussed with respect to the influence of precocenes on the insect sensory system and the role of the juvenile hormone in regulation of its development.

Development of oxygen sensing in the gills of zebrafish.

Previous studies have described the morphology, innervation and O(2)-chemoreceptive properties of neuroepithelial cells (NECs) of the zebrafish gill filaments. The present work describes the ontogenesis of these cells, and the formation of functional O(2)-sensing pathways in developing zebrafish. Confocal immunofluorescence was performed on whole-mount gill preparations using antibodies against serotonin (5-HT) and a zebrafish-derived neuronal marker (zn-12) to identify the appearance and innervation of gill NECs during larval stages. NECs were first expressed in gill filament primordia of larvae at 5 days postfertilization (d.p.f.) and were fully innervated by 7 d.p.f. In vivo ventilation frequency analysis revealed that a behavioural response to hypoxia (11.2+/-2.8 min(-1)) developed in embryos as early as 2 d.p.f., and a significant increase (P<0.05) in the ventilatory response to hypoxia (200.8+/-23.0 min(-1)) coincided with innervation of NECs of the filaments. In addition, exogenous application of quinidine, a blocker of O(2)-sensitive background K(+) channels in NECs, induced hyperventilation in adults in a dose-dependent manner and revealed the development of a quinidine-sensitive ventilatory response in 7 d.p.f. larvae. This study shows that NEC innervation in the gill filaments may account for the development of a functional O(2)-sensing pathway and the hyperventilatory response to hypoxia in zebrafish larvae. At earlier stages, however, O(2)-sensing must occur through another pathway. The possibility that a new type of 5-HT-positive NEC of the gill arches may account for this earlier hypoxic response is discussed.

Oestrogen augments the fetal ovine hypothalamus- pituitary-adrenal axis in response to hypotension.

In the fetal sheep, parturition is triggered by an increase in the activity of the fetal hypothalamus- pituitary-adrenal (HPA) axis which, in turn, augments the biosynthesis of oestrogen by the placenta. Parturition can be prevented or delayed by destruction of the paraventricular nucleus (PVN), pituitary or adrenal, or stimulated by infusions of adrenocorticotropin (ACTH) or glucocorticoids. We have previously reported that physiological increases in fetal plasma concentrations of oestradiol have a neuroendocrine effect to increase both basal and hypotension-stimulated ACTH secretion. The present study was performed to test the effect of oestradiol on the central baroreceptor and chemoreceptor reflex pathways. We used immunohistological techniques to identify various neuroanatomical regions which are activated by hypotension and, subsequently, those areas modified by oestrogen's action and baroreceptor and chemoreceptor denervation. We assessed cellular activation in these brain regions by immunostaining for Fos, the protein product of c-fos, an immediate early response gene. We found that oestradiol increased Fos abundance in nucleus tractus solitarius (NTS), rostral ventrolateral medulla (RVLM), and PVN, and augmented the increase in Fos in these regions in response to a 10 min period of brachiocephalic arterial occlusion (BCO). Carotid sinus denervation blocked the Fos response to BCO, but not to oestrogen alone, in these regions. In contrast, the hippocampus responded to BCO with increase Fos in intact fetuses, but did not respond to oestrogen treatment. None of the treatments altered Fos expression in cerebral cortex or in cerebellum. We conclude that oestradiol augments the activity of the central baroreceptor and chemoreceptor reflex pathways, and that it may influence fetal ACTH secretion via this site of action.

Fine structure and immunocytochemistry of a new chemosensory system in the Chiton larva (Mollusca: Polyplacophora).

Combined electron microscopy and immunocytochemistry of the larvae of several polyplacophoran species (Chiton olivaceus, Lepidochitona aff. corrugata, Mopalia muscosa) revealed a sensory system new to science, a so-called "ampullary system." The cells of the "ampullary system" are arranged in four symmetrically situated pairs lying dorsolaterally and ventrolaterally in the pretrochal part of the trochophore-like larva and they send axons into the cerebral commissure. They are lost at metamorphosis. The fine structure of these cells strongly resembles that of so-called "ampullary cells" known from various sensory organs of other molluscs, such as the apical complex of gastropod and bivalve larvae, osphradia of vetigastropods, and olfactory organs of cephalopods, and nuchal organs of certain polychaetes. The ampullary cells and their nerves are densely stained by anti-FMRF-amide fluorescence dyes, whereas antiserotonin staining is only weak. While cytological homology of the ampullary cells with those of other organs is probable, the ampullary system as a whole is regarded as a synapomorphy of the Polyplacophora or Chitonida.

Distal-less expression in embryos of Limulus polyphemus (Chelicerata, Xiphosura) and Lepisma saccharina (Insecta, Zygentoma) suggests a role in the development of mechanoreceptors, chemoreceptors, and the CNS.

The homeobox gene Distal-less (Dll) is well known for its participation in the development of arthropod limbs and their derivatives. Dll activity has been described for all groups of arthropods, but also for molluscs, echinoderms and vertebrates. Generally, Dll participates in the establishment of the proximo-distal-axis and differentiation along this axis. During our investigation of the expression pattern in the silverfish Lepisma saccharina and the horseshoe crab Limulus polyphemus, we found several expressions in late stages which cannot be explained with the "normal" limb-specific function. The antenna, cerci and terminal filament of the silverfish show a striped expression; single cells on the labrum, mandibles, maxillary palps and anal valves are also strongly stained by the Dll antibody. In addition to cell groups in the developing ganglia of the CNS, in the coxal endites and several nerve cells in femur and the trochanter of the prosomal limbs, the whole prosomal shield of Limulus polyphemus is surrounded by Dll-positive cell clusters. Furthermore, the lateral processes of the opisthosoma and the edges of the opisthosomal appendages are Dll positive. To get an indication of the cell fate of these regions, we examined hatched larvae and juvenile stages of both species with the SEM. We found a striking correlation of these Dll-positive areas and different sense organs, especially mechanoreceptors. Since many sense organs in arthropods are situated on the limbs, interpretation of the Dll expression in limbs is problematical. This has critical implications for comparative analysis of Dll expression patterns between arthropods and for the claim of homology between limb-like structures. Furthermore, we discuss the possibility of convergent appendage evolution in various bilaterian groups based on the improvement of spatial sensory resolution.

Postnatal maturation of carotid body and type I cell chemoreception in the rat.

The site of postnatal maturation of carotid body chemoreception is unclear. To test the hypothesis that maturation occurs synchronously in type I cells and the whole carotid body, the development of changes in the intracellular Ca2+ concentration responses to hypoxia, CO2, and combined challenges was studied with fluorescence microscopy in type I cells and compared with the development of carotid sinus nerve (CSN) responses recorded in vitro from term fetal to 3-wk animals. Type I cell responses to all challenges increased between 1 and 8 days and then remained constant, with no multiplicative O2-CO2 interaction at any age. The CSN response to hypoxia also matured by 8 days, but CSN responses to CO2 did not change significantly with age. Multiplicative O2-CO2 interaction occurred in the CSN response at 2-3 wk but not in younger groups. We conclude that type I cell maturation underlies maturation of the CSN response to hypoxia. However, because development of responses to CO2 and combined hypoxia-CO2 challenges differed between type I cells and the CSN, responses to these stimuli must mature at other, unidentified sites within the developing carotid body.

Chemosensory learning in the chicken embryo.

Prenatal chemosensory learning has been demonstrated in mammals, fish, amphibians, and insects, but not birds, although there is evidence of the avian's ability to learn auditory stimuli before hatching. This paper examines how exposure to a chemosensory stimulus (strawberry) prior to hatching affects subsequent chemosensory preferences of newly hatched chicks. The chicks' preferences were assessed at 2 days after hatching using an "olfactory" preference test (strawberry-smelling shavings versus water-coated shavings) and at 4 days after hatching using a "gustatory" preference test (strawberry-flavoured water versus unflavoured water). Chicken embryos were exposed to strawberry from Day 15 to Day 20 of incubation by either presenting the odour in the air around the egg, rubbing it onto the shell, or injecting it into the air space. With no exposure to strawberry before hatching, strawberry was highly aversive to chicks after hatching. However, following exposure to strawberry before hatching, chicks expressed a greater preference for (or weaker aversion to) the strawberry stimulus. Chicks exposed to strawberry before hatching drank more strawberry-flavoured water and spent more time in a strawberry-scented area than chicks having no exposure before hatching. This change in preference was specific to the stimulus experienced before hatching and was present in the absence of any posthatching exposure to the stimulus. The results demonstrate that a chick's chemosensory preferences are changed as a result of experience with a stimulus before hatching and are suggestive of learning. The results, similar to those obtained in other animal groups, indicate the universality of "prenatal" chemosensory learning in the animal kingdom. A possible role of embryonic chemosensory learning for recognition is discussed.

Olfactory function in the human fetus: evidence from selective neonatal responsiveness to the odor of amniotic fluid.

This study was aimed at characterizing the level of specificity of the human newborn's response to an odor experienced in utero. Three groups of breast-fed infants and 3 groups of bottle-fed infants were examined on Postnatal Day 3 for their differential head-turning response when exposed to paired-choice tests contrasting the odors of either familiar (f) amniotic fluid (AF) or nonfamiliar (nf) AF or either of these AF odors and a control (C) stimulus. In fAF versus nfAF tests, the infants oriented preferentially to the odor of fAF, regardless of their feeding regimen (i.e., of their postnatal reexposure to AF-like cues in maternal milk). The fAF or nfAF versus C tests showed that this response pattern was caused by a true positive orientation toward fAF and not by avoidance from nfAF odor. This highly selective neonatal response to fAF odor is consistent with the hypothesis that the human fetus can detect and store the unique chemosensory information available in the prenatal environment and that this information becomes coupled with positive control of behavior.

Behavioral responses of the chronically instrumented sheep fetus to chemosensory stimuli presented in utero.

Fetal sheep were surgically prepared on Days 113-114 of gestation with an array of chronic instruments for recording electromyographic data (EMG) in oral--facial, axial, and limb muscles and heart rate (FHR). Fetuses also were fitted with an intraoral catheter for infusion of chemosensory fluids (isotonic saline, quinine, colostrum, sucrose) onto the surface of the tongue. Individual subjects received chemosensory infusions on Days 134-137. Fetuses showed consistent oral responses to quinine and milk, but did not respond to isotonic saline or sucrose. Different patterns of motor responses suggest that fetuses discriminated among different concentrations of quinine. The expression of tachycardia to quinine and bradycardia to milk also suggested differential responding to chemosensory fluids that differ in hedonic qualities. Detailed characterization of fetal responses to these stimuli in utero confirm the functionality of the gustatory system in the sheep fetus near term.

The ontogeny of nasal chemical senses in garter snakes.

The development of the nasal chemical senses of reptiles is of particular interest since evidence suggests that neonatal reptiles use both their olfactory and vomeronasal systems. This review focuses on the embryonic development of these nasal chemosensory systems in garter snakes (Thamnophis spp.). Three approaches have been used to examine development: (1) Normal morphological studies, (2) 3H-thymidine autoradiographic studies, and (3) metabolic mapping of the accessory and main olfactory bulbs with cytochrome oxidase histochemistry. In addition, garter snake embryos have been grown in vitro to facilitate experimental procedures. The results of these studies show that reptiles are a rich and diverse group for investigating the developmental processes that form the neurobiological basis for naturally occurring chemosensory-mediated behaviors.

Olfaction in utero: can the rodent model be generalized?

In this article we discuss five requirements that theoretically must be fulfilled for transnatal chemosensory learning to occur in three placental species, the rat, the sheep, and the human, viz. (1) minimum or partial maturity of nasal chemoreceptor systems, (2) efficient odorivector compounds in the fetal environment, (3) the ability to memorize chemosensory information across birth, (4) perinatal continuity in chemical signals, (5) neonatal ability to detect air-borne odorants previously experienced in the aquatic environment. A substantial body of data is reviewed for the rat, in which fetal chemosensation is now firmly established. The less studied ovine perinate also shows preliminary evidence of nasal chemoreception and of postnatal retention of prenatally experienced odorants. Concerning the human species, we discuss extensive anatomical data supporting nasochemoreception in utero, but as yet no direct or indirect functional demonstration is provided. Furthermore, the strongest evidence of odorivector compounds in amniotic fluid is from human data. The results presented allow generalization of chemosensory functioning in utero in the species considered.

Ultrastructure of the human vomeronasal organ.

Virtually all vertebrates have a vomeronasal system whose involvement in pheromone detection plays a crucial role in reproduction. In humans, the vomeronasal organ has been assumed to be vestigial or absent and without functional significance. In the present study involving over 400 subjects, vomeronasal pits were observed in all individuals except those with pathological conditions affecting the septum. Electron microscopy of the adult human vomeronasal organ indicates the presence of two potential receptor elements in the pseudostratified epithelial lining: microvillar cells, and unmyelinated, intraepithelial axons. In addition, unmyelinated axons are common in the lamina propria surrounding the organ. They appear to constitute the components essential for a functional chemosensory system, and may thus provide the basis for a pheromone detection system as in other animals.

Rat fetuses respond to chemical stimuli in gas phase.

Fetuses exhibit behavioral responses to intraoral infusions of chemical solutions presented in liquid phase, including an increase in overall activity and the production of a species-typical action pattern, facial wiping. A series of experiments were conducted in which chemical compounds with strong olfactory characteristics--citral and cyclohexanone--were presented in gas phase to rat fetuses on day 20 of gestation. Fetuses exhibited similar behavioral responses to stimuli presented in liquid and gas phases, suggesting a common basis for the processing of prenatal chemosensory information. Chemosensory stimuli in gas phase are sufficient to elicit both behavioral activation and a stereotypic action pattern of the rat fetus, patterns that anticipate postnatal olfactory-directed behavior. These results suggest that prenatal chemosensory experience, which normally occurs in an aqueous medium, may be relevant to the development of postnatal behavior that is directed by airborne olfactory cues.

Neurogenesis in the vomeronasal epithelium of adult garter snakes: 3. Use of H3-thymidine autoradiography to trace the genesis and migration of bipolar neurons.

Use of H3-thymidine autoradiography and unilateral vomeronasal (VN) axotomy has permitted us to demonstrate directly the existence of VN stem cells in the adult garter snake and to trace continuous bipolar neuron development and migration in the normal VN and deafferentated VN epithelium in the same animal. The vomeronasal epithelium and olfactory epithelium of adult garter snakes are both capable of incorporating H3-thymidine. In the sensory epithelium of the vomeronasal organ, H3-thymidine-labeled cells were initially restricted to the base of the undifferentiated cell layer in animals surviving 1 day following H3-thymidine injection. With increasing survival time, labeled cells progressively migrated vertically within the receptor cell column toward the apex of the bipolar neuron layer. In both the normal and denervated VN epithelium, labeled cells were observed through the 56 days of postoperative survival. In the normal epithelium, labeled cells were always located within the matrix of the intact receptor cell columns. However, labeled cells of the denervated epithelium were always located at the apical front of the newly formed cell mass following depletion of the original neuronal cell population. In addition, at postoperative days 28 and 56, labeled cells of the denervated VN epithelium achieved neuronal differentiation and maturation by migrating much farther away from the base of the receptor cell column than the labeled cells on the normal, unoperated contralateral side. This study directly demonstrates that basal cells initially incorporating H3-thymidine are indeed stem cells of the VN epithelium in adult garter snakes.(ABSTRACT TRUNCATED AT 250 WORDS)

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.