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We here describe abundant new fossil material of amphibians and reptiles from different late Neogene localities of northern Greece: the Early Pliocene (MN 14) of Spilia 0, Spilia 1, and Spilia 2; the Early Pliocene (MN 15) of Spilia 3, Spilia 4, Spilia 5, and Vevi; and the Late Miocene or Pliocene of Chalicorrema and Rema Marmara. These new late Neogene herpetofaunas are highly diverse, documenting a considerably rich herpetofauna allowing the identification of at least two salamander, seven frog, two turtle, seven lizard, and eight snake taxa. Salamanders are represented by the salamandrid genera Ommatotriton and Ichthyosaura. Frogs are represented by the bombinatorid Bombina, the discoglossids Latonia cf. ragei and Latonia sp., the pelobatid Pelobates aff. praefuscus and Pelobates sp., the ranids Pelophylax and Rana cf. dalmatina, the hylid Hyla gr. arborea, and the bufonid Bufotes gr. viridis. Turtles are represented by the emydid Emys and an indeterminate geoemydid. Lizards are represented by the scincid Ophiomorus, two lacertids (one of which potentially pertaining to Lacerta), amphisbaenians, agamids, the anguid Pseudopus, and a potential varanid. Snakes are represented by the erycid Eryx, the natricid Natrix aff. rudabanyaensis, a small-sized elapid, an "Oriental viper", the colubriforms Periergophis and Paraxenophis, as well as two further distinct but still indeterminate morphotypes of colubriforms. For the material from Spilia tentatively referred to Ommatotriton, this is only the third occurrence in the fossil record globally. The new material of Ichthyosaura and Bombina mark the first documentation of these genera in the Greek fossil record. Abundant cranial and postcranial material from Spilia is tentatively referred to Latonia ragei, a taxon previously known from the Early Miocene of Western Europe. The new record of Pelobates represents the oldest documented occurrences of the genus in the Greek fossil record. Interestingly, the Pelobates from Spilia bears much resemblance to an extinct taxon, Pelobates aff. praefuscus, which is otherwise known from the Late Miocene of the Caucasus, and not to the extant species that currently inhabits the area. The identification of Pelophylax and Rana adds to the rather poor Neogene record of ranids from Greece. Particularly for the case of Rana cf. dalmatina from Spilia 4, this corresponds to the only documented occurrence of this extant taxon in the Greek fossil record. Similarly, the identification of Hyla gr. arborea in Spilia 1, Spilia 3, and Spilia 4, marks only the third documented occurrence of this genus in the Greek fossil record. The Bufotes material from Spilia 1, Spilia 3, and Spilia 4 represents the first documented fossil occurrence of the extant Bufotes viridis complex in Greece. The material of Emys gr. orbicularis from Vevi marks the only known pre-Quaternary record of the genus in Greece and one of the only few Neogene members of the genus known from Europe. The scincid Ophiomorus is identified in Spilia 4, known from several cranial and postcranial remains, well outside the extant range of the genus. Practically, the Spilia Ophiomorus is only the fourth known fossil occurrence of this extant genus globally and also represents one of its oldest known occurrences. Material from Spilia 1 and Spilia 3 is tentatively referred to cf. Lacerta sp., and this would mark the first known occurrence of this emblematic extant genus in the Greek fossil record, denoting the presence of the genus since at least the Early Pliocene. The new amphisbaenian specimens from Spilia 4 add to the recently described single vertebra from the same locality, and represent the youngest occurrence of amphisbaenians from continental Eastern Europe. The new agamid material from Vevi and Chalicorrema add substantially to the record of this group, which was in Greece so far known exclusively from the latest Miocene/earliest Pliocene of Maramena. A similarly important addition is the record of Pseudopus from Spilia 4, as this genus had been known in the Greek fossil record only from a very few localities. The potential varanid from Spilia represents one of the few Pliocene occurrences of this group in Europe. We identify Natrix aff. rudabanyaensis among the material from Spilia 0, Spilia 4, and Vevi, adding to the previously known record of this taxon from Maramena, however, its precise species level assignment should await a revision of Neogene European Natrix spp. The find of a small elapid from Spilia 4 represents the youngest occurrence of a coral snake from Europe, extending their statigraphic range up to the Early Pliocene (MN 14). Periergophis and Paraxenophis, two bizarre snakes, so far exclusively known from their type locality in Maramena, could be also present here, even if tentatively identified. Most notably, the new material from these localities comprises forms that are now extinct (e.g., Periergophis and Paraxenophis) or extirpated from Europe (e.g., Latonia, Varanidae, Elapidae) but at the same time also loudly attests the emergence of the extant genera that dominate the extant herpetofaunas of Greece (Ichthyosaura, Bombina, Pelobates, Pelophylax, Rana, Hyla, Bufotes, Emys, Ophiomorus, Lacerta, Pseudopus, Eryx, and Natrix), for some of which their fossil record is documented here for the first time in the area. [ABSTRACT FROM AUTHOR]

Microplastics (MPs), tiny plastic particles less than 5 mm in size, have emerged as a common and worrying pollutant in marine, freshwater, and terrestrial environments worldwide. In this study, we revealed the microplastic exposure of two endemic newt species for Türkiye. We found that polyethylene terephthalate (PET) was the predominant microplastic polymer type in both species, with the blue fiber shape in particular. We also found that there was a negative correlation between microplastic size and gastrointestinal tract (GIT) weight, but there was no significant difference between body length and GIT weight of both species. Our findings might be surprising as the studied species live in natural spring waters in remote, high-altitude areas. However, the detection of water bottles in their habitats appears to be the reason for their exposure to microplastic pollution. Therefore, reducing the use of single-use plastics is predicted to contribute to the conservation of these endemic newts. [ABSTRACT FROM AUTHOR]

Olfaction is an important mechanism of orientation in amphibians toward the breeding site. It is known that anurans can memorize the odor of the native pond during larval development and prefer this odor prior to the beginning of dispersion. However, such a mechanism in urodeles has not been studied yet. We conducted experiments on recognition of the odor of a native water body in juveniles of the smooth newt Lissotriton vulgaris. One group of larvae were reared in pure water (control), the other group in water with morpholine (10–7 mol/L). A few days after metamorphosis, the newts were tested under paired-choice conditions in a T-maze. A total of 73 newts from the experimental group and 47 newts from the control group were tested. The results of the experiment show that the newts in the experimental group preferred the morpholine solution, whereas the individuals of the control group made the choice randomly. We conclude that newts can learn the odor of the environment in which they developed and use this memory for orientation in later stages of life. [ABSTRACT FROM AUTHOR]

Extant amphibians are divided into three distinct lineages: Gymnophiona, Urodela, and Anura. Owing to their diversity, they are widely used in research concerning, among others, tissue regeneration. Here, we describe larval myotomal myogenesis in the Chinese fire-bellied newt, Hypselotriton orientalis. Morphological, ultrastructural, cytochemical, and immunohistochemical analyses showed that trunk muscles grow through hypertrophy and hyperplasia mediated by the expression of typical myogenic factors, such as Pax7, from muscle progenitor cells. Our findings also suggest a third alternative mechanism for muscle growth involving the muscle splitting or fragmentation of preexisting larval myotubes. [ABSTRACT FROM AUTHOR]

Urodelan amphibian larvae develop three pairs of branching external gills on both sides of the pharyngeal region, and this study focuses on motile cilia on the gill surface. High-speed camera was used to observe ciliary strokes on the surface of the external gills of Pleurodeles waltl larvae. We found that the directionality of ciliary beating is position-dependent on the gill surface, and this rule is applicable to all the samples examined. For visualizing water flow around the external gills, we used bead suspensions. We revealed continuous anterior-to-posterior water flow generated by coordinated ciliary beating. Around the frontal surface of the gill stem (gill rachis), water flows countercurrent to the bloodstream beneath the gill epidermis. These results suggest that ciliary beating in each ciliated cell is coordinated, which cooperatively generates continuous and directional ciliary flow. We next visualized the overall distribution of ciliated cells on the gill surface by immunostaining of acetylated alpha-tubulin. Our results showed that the fine branches of external gills (fimbriae) have a circumferential distribution of cilia aligned orthogonal to the longitudinal axes of fimbriae, which facilitates water flow from proximal to the distal part of the fimbriae through the gills. This ciliary distribution pattern and directionality of cilia-driven flow are shared among five urodelan and two anuran species. Taken together, our findings suggest that the distribution and motility of ciliated cells on the surface of external gills is finely controlled, and this might support efficient respiration by the gills in urodeles. [ABSTRACT FROM AUTHOR]

G. Kingsley Noble reported the possibility of orbital gland involvement in reproduction of spelerpine salamanders, particularly Eurycea, through rudimentary gross examination of the heads of male and female salamanders. In his report, Noble provided details from only one taxon of salamander, E. bislineata. To examine the variability of orbital glands with secondary sexual function in Eurycea, orbital glands of E. longicauda were assessed for sexual dimorphism and a distinct seasonal secretory cycle that mirrored the reproductive cycle. Orbital glands were found not to be sexually dimorphic in E. longicauda and possessed constant secretory activity in males and females throughout the year. Known secondary sexual glands (mental glands, caudal courtship glands, and cloacal glands) were sexually dimorphic between males and females and possessed a secretory cycle that could be correlated with events of the reproductive cycle, particularly mating activity. Thus, no evidence was found for orbital gland involvement in reproduction in E. longicauda. Orbital glands of both male and female E. longicauda are morphologically identical and produce copious lipoproteins throughout the year. Orbital gland secretions are potentially involved in lubrication of the eye and the prevention of fluid evaporation from the eye as described for lipoprotein secretions in other vertebrate lineages. [ABSTRACT FROM AUTHOR]

The highest potencies of regeneration in tailed amphibians in comparison with the abilities of organ and tissue restoration in other vertebrates represent the goal of longstanding and intense studies. Accumulated information can half-open some mysteries of cellular and molecular fundamentals of regeneration in Urodela, but it does not explain the maintenance of regenerative abilities in mature, adult animals. The information summarized in the review suggests that the paedomorphosis inherent in this animal group determines the keeping of the juvenile state on all levels of organization-from organismic to molecular. This, in turn, permits and eases initiation and development of regenerative responses to trauma, right up to the epimorphic regeneration of whole organs. As an example, we have traced paedomorphosis-associated cellular and molecular specificities of urodelean eye and brain tissues, which could possibly play a permissive role in their complete regeneration. [ABSTRACT FROM AUTHOR]

A new crown-group salamander, Kiyatriton krasnolutskii sp. nov., from the Middle Jurassic (Bathonian) Itat Formation of the Berezovsk Quarry locality in Western Siberia, Russia, is described on the basis of new material and a dentary fragment previously referred to the undescribed salamander taxon 'Berezovsk salamander B' (sensu Skutschas). Kiyatriton krasnolutskii sp. nov. differs from K. leshchinskiyi (type species of the genus Kiyatriton) in that the ventrolateral ridges on the atlas are sharper anteriorly, more ventrally oriented and reach the anterior cotylar rims and that the dentary has a relatively taller dental parapet. Kiyatriton krasnolutskii sp. nov. is one of the oldest salamanders in the fossil record. The finding of Kiyatriton krasnolutskii sp. nov. in Berezovsk Quarry is significant for: (1) clarifying that the previously reported 'Berezovsk salamander B' is a crown-group salamander of the genus Kiyatriton; (2) extending the stratigraphic range of the genus Kiyatriton backward some 40 million years into the Bathonian, from the previously youngest record in the Aptian-Albian; (3) indicating that K. leshchinskiyi from the Aptian-Albian Shestakovo locality in Western Siberia, Russia, survived as a relic into the Early Cretaceous of present-day Western Siberia; (4) supporting the hypothesis that Bathonian vertebrate faunas of Europe and Western Siberia were homogeneous; and (5) suggesting that all Bathonian crown-group salamanders in Asia could be members of one cryptobranchoid clade and could represent the first radiation of Cryptobranchoidea. [ABSTRACT FROM AUTHOR]

During amphibian metamorphosis, modifications of several important body systems take place involving different molecular mechanisms driving, among other, cell differentiation, cell-cell adhesion, and extracellular matrix turnover. Amphibians have been used as a classic model to investigate organs remodelling, including the skin; however, previous studies on metamorphosis have examined, for the most part, anurans, whereas only a few reports have considered urodeles. The main goal of this study was to evaluate the presence of keratins in the epidermis of the Italian newt ( Lissotriton italicus). In order to assess the putative differential expression of keratins, we immunodetected cytokeratin type I, type II, and high molecular weight (HMW) during the larval, pre-metamorphic, and adult phase. Our results clearly indicated that keratins expression changes as the epidermis modifies during the functional maturation; interestingly, HMW keratins showed a strong immunopositivity in adult, thus suggesting that, in urodeles, these keratins become expressed in adult epidermis. Moreover, by using a monoclonal antibody against pan-cadherin, we demonstrated that in L. italicus epidermis during pre-metamorphic stages, the conversion from larval to adult type is not completed in whole epidermis; we also showed the strong spatiotemporal correlation of stromelysin-3 expression with tissue remodelling in L. italicus skin. Considering that skin remodelling in urodeles is a topic relatively neglected, our findings will contribute to fill a gap in the existing research literature; moreover, these data emphasize that unexpected results could be obtained when different model systems were used. [ABSTRACT FROM AUTHOR]

We document the successful establishment of a European newt ( Lissotriton vulgaris) in south-eastern Australia, the first recorded case of a caudate species establishing beyond its native geographic range in the southern hemisphere. Field surveys in south-eastern Australia detected L. vulgaris at six sites, including four sites where the species had been detected 15 months earlier. Larvae were detected at three sites. Individuals had identical NADH dehydrogenase subunit 2 and cytb mtDNA gene sequences, and comparisons with genetic data from the species' native range suggest that these individuals belong to the nominal subspecies L. v. vulgaris. Climatic conditions across much of southern Australia are similar to those experienced within the species' native range, suggesting scope for substantial range expansion. Lissotriton vulgaris had been available in the Australian pet trade for decades before it was declared a 'controlled pest animal' in 1997, and thus the invasion documented here likely originated via the release or escape of captive animals. Lissotriton vulgaris is the sole member of an entire taxonomic order to have established in Australia, and given the potential toxicity of this species, further work is needed to delimit its current range and identify potential biodiversity impacts. [ABSTRACT FROM AUTHOR]

Available information on the development of primitive urodele (Hynobiidae) limbs and limb structure in Devonian tetrapods provide the basis for formulating the hypothesis on the existence of a special phase, the phase of the biserial limb in tetrapod history. The limb of the Devonian amphibian Ichthyostega with two groups of digits, preaxial and postaxial, corresponds well to this phase. Based on the structure of the Ichthyostega limb, it is suggested that the fin type ancestral to terrestrial limbs was asymmetrical biserial, possessed a short axis, unbranched jointed preaxial radials deviating one by one from each mesomere of the axis, and unbranched jointed postaxial radials deviating from the distal mesomeres of the axis in two or more radials. [ABSTRACT FROM AUTHOR]

We describe ten microsatellite loci isolated for the oldest lineage of extant salamandrids, the spectacled salamanders ( Salamandrina), a genus of terrestrial salamanders endemic to the Apennine peninsula (Italy). Primers were tested in 24 individuals per species, the northern species ( Salamandrina perspicillata) and the southern species ( Salamandrina terdigitata). All loci were polymorphic in S. perspicillata with number of alleles ranging from three to eleven and observed heterozygosity ranging from 0.25 to 0.83. In S. terdigitata eight loci were polymorphic, the number of alleles ranged from two to nine, and observed heterozygosity from 0.04 to 0.92. [ABSTRACT FROM AUTHOR]

This article present a review of species numbers, biogeographic patterns and evolutionary trends of amphibians in freshwater. Although most amphibians live in freshwater in at least their larval phase, many species have evolved different degrees of independence from water including direct terrestrial development and viviparity. Of a total of 5,828 amphibian species considered here, 4,117 are aquatic in that they live in the water during at least one life-history stage, and a further 177 species are water-dependent. These numbers are tentative and provide a conservative estimate, because (1) the biology of many species is unknown, (2) more direct-developing species e.g. in the Brachycephalidae, probably depend directly on moisture near water bodies and (3) the accelerating rate of species discoveries and descriptions in amphibians indicates the existence of many more, yet undescribed species, most of which are likely to have aquatic larvae. Regional endemism in amphibians is very high, with only six out of 348 aquatic genera occurring in more than one of the major biogeographic divisions used herein. Global declines threatening amphibians are known to be triggered by an emerging infectious fungal disease and possibly by climate change, emphasizing the need of concerted conservation efforts, and of more research, focused on both their terrestrial and aquatic stages. [ABSTRACT FROM AUTHOR]

Genetic variation in the golden-striped salamander (Chioglossa lusitanica) was assessed in 231 individuals from four Portuguese populations by means of horizontal starch gel electrophoresis and isoelectric focusing. Three of 19 enzyme systems, representing 21 presumptive loci, were found to be polymorphic: phosphoglucomutase 1 (PGM1), peptidase B (PEPB), and peptidase D (PEPD). The observed average heterozygosity in Chioglossa lusitanica (0.027) is significantly lower than that observed for other amphibians, either urodeles or salamandrids. Differences in allele frequencies and the presence of private alleles are indicative of a high degree of population differentiation. PEPD, in particular, seems to be a diagnostic locus separating the southernmost population studied from the others. [ABSTRACT FROM AUTHOR]

An immunocytochemical investigation was made of the distribution of serotonin (5-HT) in the brain of larval and adult Ambystoma mexicanum and adult Typhlonectes compressicauda. Immunoreactive perikarya can be identified in the caudal diencephalon (paraventricular organ and infundibular nucleus), in the ventral mesencephalon (interpeduncular nucleus) and in the raphe of the rhombencephalon. Immunopositive fibers and terminal arborizations are widely distributed, extending from the whole telencephalon to the spinal lemniscus area. However, the retinorecipient structures of the thalamus and mesencephalon are either very weakly innervated ( Ambystoma) or completely immunonegative ( Typhlonectes). The habenular system also exhibits very few 5-HT-positive structures. The major serotoninergic neuron clusters, in both Urodela and Gymnophiona, tend to gather, from the paraventricular organ to the raphe, on both sides of the sagittal plane, showing no tendency to 'lateralization'. A new interpretation of the limited development of the serotoninergic system in amphibians is given. [ABSTRACT FROM AUTHOR]

The ependymal junction pattern in the spinal cord of postmetamorphic ribbed newts has been studied, using transmission electron microscopy of ultrathin sections of normal animals and of animals perfused through the IVth ventricle with lanthanum. Contrary to what has been observed in mammalian CNS, the ependyma of the urodelan spinal cord is furnished with tight junctions that seal the luminal border of the terminal bars. These occludens junctions are made up of two to seven punctate fusions of the plasma membranes. Lanthanum tracer remains restricted inside the lumen of the central canal, being stopped at the first punctate fusion on its way through the intercellular clefts. Beyond this point, the extracellular space contains no tracer material. Besides tight junctions, intermediate, desmosomal and gap junctions are also present. Gap junctions and desmosomes are not present in CSF-contacting neurons. It is suggested that ependyma with occluding junctions (special ependyma) overlay the regions of the CNS where the ependymal cells significantly modify the composition of both intercellular and cerebrospinal fluids, through secretory, transporting and permeability control activities. [ABSTRACT FROM AUTHOR]

Although the photomechanical response of the iris in amphibians has been characterized, the central pathway of reflex control is unknown. We investigated this pathway by electrophysiological and anatomical techniques in urodeles. Sustained responding neurons in the pretectum were localized and characterized. Three neuron types were found and compared with tonic neurons in mammals. They were driven by the contralateral retina and their dendrites arborized in the pretectal neuropil. The localization of cell bodies resulted in the identification of a physiological nucleus comparable with the nucleus praetectalis olivaris. It was shown that the tonic neurons project ipsi- and contralaterally to the oculomotor region, where axons terminate in deep layers of the stratum album. Using horseradish peroxidase transport the ciliary ganglion in urodeles was identified. It occurs in ontogenesis parallel to the first detectable pupillary light reflex corresponding to the onset of metamorphosis. [ABSTRACT FROM AUTHOR]

The incidence and ultrastructure of satellite cells in the tail muscles of urodelan larvae were examined during development during which the number of satellite cells is gradually reduced. They are found more frequently in red than in the white fibres in all four stages examined (stage 53, 64, 66 and juvenile). As development proceeds, intercellular space between satellite cell and muscle fibre is in general gradually extended and is mostly filled with basal lamina. Small muscle cells, satellite fibres, which are situated under the basal lamina of the parent fibre, are morphologically similar to satellite cells but contain a small amount of myofibrils. Three types of satellite fibres are distinguishable on the basis of differences in K-EDTA-treated ATPase activity, width of Z line, and parent fibre type. Neuromuscular junctions are visible in satellite fibres. [ABSTRACT FROM AUTHOR]

The pituitary glands of two urodelan species ( Mertensiella caucasica, Triturus cristatus) and one caecilian species ( Chthonerpeton indistinetum) were examined with histological (Alcian blue, Brookes' trichrome stain), enzyme histochemical (acid phosphatase, α-naphthylacetate-esterase, acetylcholinesterase) and immunofluorescence techniques (anti-carp GTH, anti-ovine prolactin, anti-synthetic α-MSH). In the pituitary gland of Mertensiella and Triturus six chromophilic cell types could be distinguished. A strong fluorescence was observed in the MSH-, GTH- and TSH-cells. In the pituitary gland of Chthonerpeton only five chromophilic cell types could be distinguished: in the rostral part of the pituitary gland the B-cell; in the basal region of the central area the B-cell; dorsocaudally the B-cell. The acidophilic cells were found in the central and caudal part of the pars distalis. The basophils of the pars intermedia could be observed in the dorsocaudal part of the pituitary gland surrounding the neurohypophysis. All acidophilic cells showed a strong immunofluorescence with anti-ovine prolactin (LTH). [ABSTRACT FROM AUTHOR]

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Oogenesis was studied in adult Triturus vulgaris (Urodela) with the electron microscope. The oocytes investigated ranged between 50 μm and 1600 μm in diameter. Two types of yolk platelet formation were found. Since both types involve the incorporation of high numbers of pinocytotic vesicles they are believed to be of an extraoocytic origin. On the basis of the order of their appearance they were named primary and secondary yolk. Five different types of vesicles were found, which participate in a variety of activities, such as yolk formation and the formation of the Golgi apparatus. They originate from four different sources, namely the nuclear membrane, the cytoplasm in connection with ribosome-like particles, the Golgi apparatus and the plasma membrane through pinocytosis. The results obtained were discussed especially with respect to differences found between the anura and the urodela, such as the presence or absence of cortical granules or equivalent structures. [ABSTRACT FROM AUTHOR]

Ectopic differentiation of retinal structures in contact with the pituitary, after insertion of a methylene blue stained celloidin lamina at the level of the median eminence was observed in the adult crested newt ( Triturus cristatus carnifex Laur.). Retinal components ranging from pigmented cells to early retinal vesicles and fully developed neural retina and visual cells are described. Indications pointing to the ependymal cells which line the infundibular sac sequestered between the intermediate lobe and the pars distalis, as the source of the neural retina and visual cells are presented. [ABSTRACT FROM AUTHOR]

Dorsal tubercle and skin of Mertensiella caucasica have been investigated with the electron microscope and enzyme histochemical methods. The epidermis of the tubercle consists of 8-9 cell layers, that of normal dorsal skin of 5-6. The tubercle is filled with large mucous glands which are surrounded by an almost complete layer of smooth muscle cells (myoepithelial cells). Their glandular cells undergo cyclical changes and are characterized by specific secretory granules, which differ from those of the relatively small mucous glands of the normal dorsal skin. In the connective tissue of the tubercle a relatively rich supply of nerve fibres has been found, which in part contain synaptic and dense core vesicles or accumulations of mitochondria. In the normal dorsal skin nerve fibres occur less frequently. The following enzymes have been demonstrated in the mucous glands of the tubercle: SDH, acid phosphatase, unspecific esterases, E 600 resistant esterase. The tubercle seems to stimulate the female cloaca chemically and mechanically. [ABSTRACT FROM AUTHOR]

Golgi methods were employed to study neurons and ependymal tanycytes in the posterior hypothalamus of the newt. The tanycytes send a few coarse, spiny or barbed processes towards the pia mater. In the periventricular grey, the neurohistological methods show common neurons, ranging from a multipolar to a plumed organization, and abundant liquor-contacting cells. These cells, possibly neurons, give rise to a process that reaches the cerebro-spinal fluid, and terminates in a spindle-shaped swelling, with a thin thread at its tip. In other cells, the intraventricular endings are bulbous or finger-like. The occurrence of: (1) branches of the liquor-contacting process, running parallel to the infundibular surface; (2) infundibular processes which end at the base or between the ependymal cell bodies; and (3) axons coursing in the same position, all indicates that the subependymal layer is a site for complex intercellular relationships. The significance of liquor-contacting cells and tanycytes is discussed, in view of the possibility that they may represent part of a system for hypothalamic regulation in response to changes in the CSF. [ABSTRACT FROM AUTHOR]