Pit Organs Research Articles

An investigation of the effects of ruthenium red, nitric oxide and endothelin-1 on infrared receptor activity in a crotaline snake

The infrared (IR) receptors in the pit organ of crotaline snakes are very sensitive to temperature. The vasculature of the pit organs, which is located in close proximity to IR-sensitive terminal nerve masses (IR receptors), is finer, flatter, and more convoluted than that of other sensory organs. Using extracellular recording in vivo from IR-sensitive primary afferent trigeminal ganglion (TG) neurons of the crotaline snake Trimeresurus flavoviridis, I studied the response to IR warming (24–25 °C) and to various chemicals: an exogenous vasoactive substance nitric oxide donor (sodium nitroprusside, SNP), endothelin-1 (ET-1), a transient receptor potential vanilloid (TRPV)1 agonist (capsaicin, CAP) and antagonist (capsazepine, CZP), and Ruthenium Red (RR), an antagonist of the TRPV family. IR-sensitive primary afferent TG neurons display regular background firing at 10–25 impulses per second at 24–25 °C. At this temperature, Ruthenium Red and endothelin-1 clearly suppressed the frequency of background firing, while sodium nitroprusside injected into the bloodstream significantly increased the frequency of discharges ( P<0.01) and caused regular bursts of firing in IR-sensitive TG neurons. By contrast, capsaicin and capsazepine had no effect on the infrared responses. The possibility that these opposite responses result from their vasoactive effects on the unusual pit vasculature or from their chemical effects on the thermoreceptors of IR-sensitive nerve terminals in the pit organ, like those of the TRPV family, is discussed.

The micromorphology of the blesbuck louse &lt;i&gt;Damalinia (Damalinia) crenelata&lt;/i&gt; as observed under the scanning electron microscope

The blesbuck is an important game animal on many game farms and reserves in South Africa. Damalinia crenelata, a biting louse, host-specific to the blesbuck, feed upon epidermal debris of this antelope, leading to severe skin irritation and dermatitis. Symptomatic scratching by the host aggravates these conditions. High infestations may lead to decreased population numbers. Live lice were collected from a blesbuck in the Rietvlei Nature Reserve and prepared for selectron microscopic investigation. Micrographs were recorded. The SEM investigation revealed several micromorphological features not previously described in D. crenelata. Besides the obvious anatomical differences in the reproductive organs of the male and female, several other differences were noted. The antennal flagellae showed morphological differences as well as certain features on the ventral surfaces of the head. Dorsally the forehead was markedly emarginated and showed an acute invagination (clypeo labral suture) in the pulvinal area. The ventral surface of the head clearly demonstrated the structures of the preantennal regions such as ventral carina, pulvinus, labrum, mandibles and clypeus. The epipharynx appeared as an underlying extension of the labrum. The rims of the clypeus were more raised and thickened in the female than in that of the male. The mandibles were not notched and were noted to be angular in shape. The three segments of each of the antennae of the male were thicker and more robust than than those of the female. This could suggest sexual dimorphism in this species. The sensilla basoconica comprised 10 pegs. Pit organs were seen within the pore organs. The prothorax and mesothorax were clearly distinguished. The abdominal segments showed six pairs of spiracles. The male andfemale terminalia were confirmed to be strongly sexually dimorphic. The three pairs oflegs each terminated in a single, long and slender, claw.

Distribution of neuropeptide Y immunoreactivity in the central and peripheral nervous systems of amphioxus (Branchiostoma lanceolatum Pallas).

Immunocytochemistry techniques were employed to investigate the distribution of neuropeptide Y-like-immunoreactive (NPY-ir) cells and fibers in the central and peripheral nervous systems of adult amphioxus. NPY-ir neurons of the commissural type were abundant in the brain and present but more scarce in the spinal cord. These neurons gave rise to conspicuous NPY-ir tracts that coursed along the entire length of the nerve cord. Some fibers exhibited conspicuous Herring body-like swellings. In the peripheral nervous system, small NPY-ir neurons and a large number of thin, beaded NPY-ir fibers were observed in the atrial region, indicating the involvement of this substance in visceral regulation. A few NPY-ir fibers, possibly afferent to the spinal cord, coursed in the ventral branches of the spinal nerves of this region, whereas no NPY-ir fibers coursed in the preoral or velar nerves or in the dorsal branches of the other spinal nerves. These results indicate that NPY is widely used as a neuroregulator/neurotransmitter in the central and peripheral nervous systems of this primitive chordate. In addition, this study demonstrates the presence of tall, thin NPY-ir cells in the putative adenohypophyseal homologue, the Hatschek's pit organ, which is located in the roof of the preoral cavity (vestibule).

The behavioural role of pit organs in the epaulette shark

Epaulette sharks Hemiscyllium ocellatum in three treatments, pit organs (free neuromasts) ablated, sham‐operated and normal (n = 8 for each treatment), showed a significant preference for facing upstream in a flume (P &lt; 0·05). There were no significant differences in the mean angles or angular variances among treatments. Individuals with ablated pit organs, however, spent significantly less time moving around than controls (P &lt; 0·05), suggesting that pit organs contributed to motivation for activity. Pit organs do not appear to make an important contribution to rheotaxis in H. ocellatum. It is suggested that this may be due to structural differences in the pit organs of H. ocellatum compared with other species.

Inter- and intraspecific variation in the distribution and number of pit organs (free neuromasts) of sharks and rays.

The distribution of pit organs (free neuromasts) has previously been documented for several species of pelagic sharks, but is relatively poorly known for rays and bottom-dwelling (demersal) sharks. In the present study, the complete distribution of pit organs was mapped in the demersal sharks Heterodontus portusjacksoni, Orectolobus maculatus, Hemiscyllium ocellatum, Chiloscyllium punctatum, and Asymbolus analis, and the rays Rhinobatos typus, Aptychotrema rostrata, Trygonorrhina sp. A, Raja sp. A, and Myliobatis australis. All of these species had pit organs scattered over the dorsolateral surface. The sharks also had "mandibular" pit organs (and "umbilical" pit organs in C. punctatum and A. analis) on the ventral surface, while pit organs were sparse or absent on the ventral surface of rays. All of the species examined here, except for M. australis, also had a "spiracular" group of pit organs adjacent to the eye and/or spiracle. Spiracular pit organs were also recorded for the sawshark Pristiophorus sp. A and the skate Pavoraja nitida, although the remainder of pit organs were not mapped in these species. The distribution and number of pit organs varied both within and among species. Pit organ distribution was asymmetrical in each individual examined, but no particular trend towards left or right "handedness" was observed in any species. Although rays have been thought to have fewer pit organs than sharks in general, this was not the case in the present study. All of the species examined here had few pit organs compared to the pelagic sharks previously documented, but it is not clear whether this is due to ecological or phylogenetic causes.

Wide-band spectral tuning of heat receptors in the pit organ of the copperhead snake (Crotalinae).

Receptors located in the facial pit organ of certain species of snake signal the presence of prey. Infrared radiation is an effective stimulus suggesting that these receptors may be low-threshold temperature receptors. We recorded from the nerve innervating the pit organ of snakes belonging to the family of Crotalinae while stimulating the receptive area with well-defined optical stimuli. The objective was to determine the sensitivity of these receptors to a wide range (0.400-10.6 micro m) of optical stimuli to determine if a temperature-sensitive or photosensitive protein initiated signal transduction. We found that receptors in the pit organ exhibited a unique broad response to a wide range of electromagnetic radiation ranging from the near UV to the infrared. The spectral tuning of these receptors parallels closely the absorption spectra of water and oxyhemoglobin, the predominant chromophore in tissue. Our results support the hypothesis that these are receptors activated by minute temperature changes induced by direct absorption of optical radiation in the thin pit organ membrane.

Immunohistochemical localization of the delta subspecies of protein kinase C in the trigeminal sensory system of Trimeresurus flavoviridis, an infrared-sensitive snake

We examined the expression of the protein kinase C (PKC) δ subspecies in the trigeminal sensory system of the infrared-sensitive snake Trimeresurus flavoviridis. In the trigeminal ganglion (TG), diffuse low-intensity PKC δ immunoreactivity was found in TG neurons and fibers, while intense reactions were observed mainly in medium-sized neurons, which include most of the infrared-sensitive neurons. In the brainstem, intense PKC δ immunoreactivity was present in the intermediate layer of the optic tectum of the midbrain and in the nucleus descendens lateralis n. trigemini of the medulla oblongata; these areas are related to the infrared sensory pathway. In the pit organ (the infrared receptor), PKC δ immunoreactivity was present in terminal nerve masses in the pit membrane. These findings suggest that the PKC δ subspecies is involved in the infrared sensory pathway in the trigeminal sensory system of the infrared-sensitive snake.

Proteome analysis of the thermoreceptive pit membrane of the western diamondback rattlesnake Crotalus atrox.

Rattlesnakes detect their prey's temperature by means of a cavern-like structure, the pit organ. The sensory component of this organ lies within a thin membrane called the pit membrane. Proteome analysis conducted on this neurosensory tissue revealed only a relatively small number of proteins, thereby depicting its high degree of specialization. In addition to containing blood serum and structural proteins, the proteome of this membrane appears to be strikingly similar to that of isolated rattlesnake brain mitochondria. Indeed, our results show that over 80% of the detected tissue proteins are of mitochondrial origin. Fluorescence microscopy studies of these organelles indicate their dense arrangement and accumulation in structures which have been previously reported to be the terminal ends of free nerve fibers of the innervating trigeminal branches. Thus, original ultrastructural observations are paralleled by our findings at the molecular level.

Response of the infrared receptors of a crotaline snake to ethanol

The pit organs of crotaline snakes can sense infrared (IR). The pit membrane has a finer, flatter, more convoluted vasculature than other sensory organs. Using extracellular recording from IR-sensitive trigeminal ganglion (TG) neurons (primary neurons) and tectal (OT) neurons of the crotaline snake Trimeresurus flavoviridis, we examined the IR response to ethanol (EtOH) in vivo. The response to EtOH was recorded in the TG and OT 20–80 s after 10% EtOH in Ringer's solution (100 μl/ 500 g body weight) was injected via the heart. The responses to EtOH and those to lower or higher temperature stimulation were additive. At a constant temperature (25 °C), EtOH significantly potentiated the IR-triggered discharges of IR-sensory pathways in this snake. These results suggest that the IR response to EtOH is due to either its vasodilatory effect on the abundant vasculature of the pit membrane or its chemical effect on temperature-sensitive receptors.

Odontode morphology and skin surface features of Andean astroblepid catfishes (Siluriformes, Astroblepidae).

Two types of odontodes, or dermal teeth, occur in the neotropical Andean astroblepid catfishes. Both odontode types conform in structure to dermal teeth of gnathostomes in having dentine surrounding a central pulp cavity covered by a superficial layer of enameloid, but differ from one another in terms of attachment and association with other epidermis features. Type I odontodes in astroblepids, also found in all representatives of the superfamily Loricarioidea, are larger (40-50 microm base diameter), generally conical and sharply pointed, occur on the fin rays, and are associated with dermal bone. Type I odontodes attach to an elevated pediment of dermal bone of the fin lepidotrich, and to dermal bone generally in loricarioids, via a ring of connective tissue. Type II odontodes of astroblepids are smaller (15-20 microm base diameter) and blunt, occur in the skin of the head, maxillary barbels, nasal flap, and lip margins, and are not associated with dermal bone. Observations based on histology and scanning electron microscopy indicate that Type II odontodes are associated with other epithelial structures to form a putative mechanosensory organ. The odontode base lies deep in the dermis. The shaft is surrounded by a dense patch of microvillous epithelium and projects from within a pit formed by an elevated ring of laminar epithelial cells bearing several columnar, knob-like putative mechanosensory structures. Type II odontode organs have thus far been observed in only three astroblepid species, Astroblepus longifilis, A. chotae, A. rosei, where they occur in especially dense arrays on the maxillary barbels, surrounded by discrete patches of microvilli and separate mechanoreceptors. Type II odontode organs are less dense elsewhere on the body, but also occur in the skin of the snout, head, and lips. Typical taste buds are absent from the barbels of these species, but present in other astroblepids. The presence of Type II odontodes and their association with specialized epithelial pit organs are unique to astroblepids among siluriforms and may be potentially important adaptations to life in torrential mountain streams.

S-100 protein is a selective marker for sensory hair cells of the lateral line system in teleosts

The distribution of S100 protein in the neuromast of the lateral line system (LLS) was investigated immunohistochemically in alevins of three species of teleosts ( Salmo trutta, Salmo salar and Dicentrarchus labrax), using a polyclonal antibody. In both the neuromasts of the canals, as well as in the pit organs, the hair cells, regarded as the specific sensory cells, displayed cytoplasmic immunoreactivity for S100 protein. Conversely, the supporting cells, mantle cells and basal cells were devoid of immunoreaction. These results demonstrate for the first time the occurrence of S100 in the LLS of teleosts. Due to the cell specific localization, this protein might serve as a marker for sensory hair cells in neuromasts.

Distribution of myelinated and unmyelinated nerve fibers and their possible role in blood flow control in crotaline snake infrared receptor organs.

We used transmission electron microscopic montages to examine the composition of nerve bundles serving the infrared pit organs of two species of crotaline snakes, Agkistrodon blomhoffii and A. brevicaudus. In the three main bundles, the myelinated fibers totaled 2,200-3,700, and unmyelinated fibers 2,400. We also discovered for the first time two accessory bundles composed almost entirely of unmyelinated fibers running alongside the main bundles, containing an average total of 3,300 unmyelinated fibers vs. an average of 10 myelinated fibers. Thus, the average total of unmyelinated fibers was nearly twice that of myelinated fibers. To study the nature of the unmyelinated fibers, we did double staining immunohistochemistry with antibodies for substance P (SP) and vasoactive intestinal polypeptide (VIP) in combination with and without capsaicin pretreatment. SP and VIP immunoreactive varicose fibers ran straight toward the center of the pit membrane in parallel with arterioles and venules, and also formed a dense network around the periphery of the membrane. There were three types of fibers: fibers containing only SP, fibers containing only VIP, and fibers containing both peptides. SP-only fibers were distributed singly throughout the pit membrane and in small bundles around the periphery. SP+VIP fibers were distributed sparsely in the pit membrane and around its periphery. VIP-only fibers were distributed throughout the pit membrane and were of smaller diameter than SP and SP+VIP fibers. After treatment with capsaicin, most of the three types of varicose fibers disappeared from the central part of the pit membrane, but those around the periphery remained unaffected. The capsaicin-sensitive fibers may be unmyelinated sensory types, and the unaffected ones may be autonomic nerve fibers.

The development of the pit organ of Bothrops jararaca and Crotalus durissus terrificus (Serpentes, Viperidae): support for the monophyly of the subfamily Crotalinae

AbstractThe development of the pit organ and the course of the lateral branch of the ethmoidal nerve of the two South American crotalines Bothrops jararaca and Crotalus durissus terrificus are described in detail using serially sectioned material from fetal stages. Serial sections of the Asian pit vipers Agkistrodon halys halys and Trimeresurus albolabris were included in this work. The viperines, as the sister‐group of the Crotalinae, and the Colubridae, Elapidae and Boidae as their outgroups were used for comparisons. New synapomorphies of the advanced subfamily Crotalinae were found: namely, absence of the foramen epiphaniale and an extracapsular course of the lateral branch of ethmoidal nerve. These results support the monophyly of the crotalines.

Immunohistochemical localization of BDNF-, TrkB- and TrkA-like proteins in the teleost lateral line system.

The lateral line system, formed of both superficial (pit organs) and canal neuromasts, is one of the major mechanosensory systems in fish. It has always been assumed that this system depends on neurotrophins and their cognate Trk receptors for development and maintenance, as has been shown in other mechanosensitive systems of vertebrates. However, until nowthis issue has not been specifically addressed. In this study we used immunohistochemistry to investigate the occurrence and localization both of neurotrophins (NGF-, BDNF- and NT-3-like) and of Trk-like proteins (TrkA-, TrkB-, TrkC-like) in alevins of Salmo salar and S. trutta. All cells in the pit organs of S. salar displayed strong immunoreactivity for TrkB-like and BDNF-like, whereas they were restricted to the hair cells in S. trutta. The hair, supporting and mantle cells of S. salar, and the mantle cells of S. trutta, also expressed TrkA-like immunoreactivity. In the canal neuromasts BDNF-, TrkA- and TrkB-like proteins were present in all cells, without differences between species. NGF-, NT-3- and TrkC-like immunoreactivity were never detected. The present results suggest that mechanoreceptive hair cells, as well as supporting cells, in the lateral line system are under the control of the BDNF-TrkB-like complex, and probably of ligands of TrkA-like receptors.

Investigation of the transduction mechanism of infrared detection in Melanophila acuminata: photo-thermal–mechanical hypothesis

Differential phase optical low coherence reflectometry (OLCR) was used to detect sub-wavelength displacements in the infrared-sensitive thoracic pit organ of Melanophila acuminata (Coleoptera: Buprestidae) upon absorption of infrared radiation at 3.39 μm. The displacement had more complex morphology but similar amplitude (∼100 nm at 1 W cm −2) when compared to the displacement measured from the exocuticle in an alternate region on the beetle's body. In addition, a simplified finite difference model was developed to predict the temperature distribution and resultant thermal expansion in the pit organ tissue. The experimental and model results were interpreted to help clarify the mechanism by which the sensilla in the pit organ convert infrared radiation to neural signals. The results of this paper are discussed in relation to the photo-thermal–mechanical transduction hypothesis. This is the first experimental examination of the transduction mechanism in Melanophila acuminata.

Infrared spectral sensitivity of Melanophila acuminata

The spectral sensitivity of the pit organ of the beetle Melanophila acuminata (Coleoptera:Buprestidae) was measured using an ultrafast tunable infrared laser source and standard electrophysiological techniques. The pit organ may be classified as a broadband detector as the beetles responded to all infrared excitation wavelengths from 2 to 6 μm. There was a decrease in response threshold and latency and an increase in the magnitude of the response in the region from 2.8 to 3.5 μm, which corresponded to a region of decreased transmittance (increased absorbance) as measured by Fourier transform infrared spectroscopy. The implications of the correlation between spectral response and optical properties are discussed.

Altered visual experience and acute visual deprivation affect predatory targeting by infrared-imaging Boid snakes

Boid and Crotaline snakes use both their eyes and infrared-imaging facial pit organs to target homeothermic prey. These snakes can target in complete darkness, but the eyes can also effectively direct predatory strikes. We investigated the behavioral correlates of boid snakes’ simultaneous use of two imaging systems by testing whether congenital unilateral visual deprivation affects targeting performance. Normally sighted Burmese pythons exhibited average targeting angle of zero (on the midline axis of the head), but three unilaterally anophthalmic Burmese pythons targeted preferentially on the sighted side. A unilaterally anophthalmic amethystine python also targeted on the sighted side, and a unilaterally anophthalmic Brazilian rainbow boa tended to target on the sighted side, though its mean targeting angle was not significantly different from zero. When unilaterally anophthalmic Burmese pythons were temporarily blinded, mean strike angle changed to that of normally sighted snakes. These results show that while infrared-imaging snakes can shift between visual and infrared information under acute experimental conditions, loss of part of the visual field during development results in abnormal predatory targeting behavior. In contrast, normally sighted snakes subjected to temporary unilateral blinding do not target preferentially on the sighted side. Therefore, while loss of part of the visual field may be compensated for by infrared input in normal snakes, partial absence of visual input during development may alter central organization of visual information. Conversely, absence of half the visual field during development does not alter targeting performance based upon infrared input alone, suggesting that organization of the central infrared map does not depend upon normal organization of visual input.

Biological infrared imaging and sensing

A variety of thermoreceptors are present in animals and insects, which aid them in hunting, feeding and survival. Infrared (IR) imaging pit organs in Crotaline and Boid snakes enable them to detect, locate and apprehend their prey by detecting the IR radiation they emit. IR pit organs of common vampire bats ( Desmodus rotundus) enable them to detect IR radiation emitted by blood-rich locations on homeothermic prey. The beetle Melanophila acuminata locates forest fires by IR-detecting pit organs in order to lay their eggs in freshly killed conifers. Thermoreceptors located in the wings and antennae of darkly pigmented butterflies ( Pachliopta aristolochiae and Troides rhadamathus plateni) protect them from heat damage while sun basking. Blood-sucking bugs ( Triatoma infestans) are speculated to possess thermoreceptors, which enable them to perceive the radiant heat emitted by homeothermic prey and estimate its temperature at a distance. This is a review of the diverse types of biological thermoreceptors, their structure and function, and how electron microscopy has been instrumental in determining their ultrastructure.

Characterization of Beetle &lt;I&gt;Melanophila acuminata&lt;/I&gt; (Coleoptera: Buprestidae) Infrared Pit Organs by High-Performance Liquid Chromatography/Mass Spectrometry, Scanning Electron Microscope, and Fourier Transform-Infrared Spectroscopy

The beetle Melanophila acuminata (De Geer) is able to detect infrared radiation emitted from forest fires with two infrared receptors (pit organs) located on the metathorax next to the coxal cavity of the second set of thoracic legs. Each pit organ houses ≈70 single IR sensilla, which probably transduce incoming IR radiation into a mechanical event. These pit organs may exhibit chemical differences from the cuticle covering other parts of the beetle, which could account for their enhanced infrared detection. Infrared pit organs and the elytra, the cuticle covering the wings, were subjected to LC/MS analysis by extracting the cuticle with solvents that varied in polarity. The resulting chromatograms and mass spectra were used to identify differences in solute mobility and composition. Energy dispersive spectroscopy and point dwell maps indicated only the presence of carbon, oxygen and nitrogen for the pit organs, wings and elytra. FT-IR transmission spectra were obtained for the pit organs, eye scales, coxal cavities and wings. FT-IR analysis detected chemical bonding for the sensilla of the pit organ, which agreed with the energy dispersive spectroscopy results. Sensilla absorb IR radiation at the maximum emission wavelength of forest fires, and there is no indication of a complex chemical reaction occurring upon IR absorption. Therefore, the degree of expansion of the cuticular apparatus of the IR sensilla seems to be the sole contributing factor for the photomechanical portion of infrared detection.

The dorso‐lateral pit organs of the Port Jackson shark contribute sensory information for rheotaxis

Resting Port Jackson sharks Heterodontus portusjacksoni with dorso‐lateral pit organs ablated oriented with a mean angle of 263° to the current direction in a flume. This was significantly different (P&lt;0·01) to controls (normal and sham operated) who had a pooled mean angle of 44° to the current. Thus the dorso‐lateral pit organs of H. portusjacksoni, like the free neuromasts of some teleosts, provide sensory information for rheotaxis.