Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Turtles”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 595 records · Page 33Linked to original sources
PubMed1990

The effects of GABA and related drugs on horizontal cells in the isolated turtle retina.

The role of GABA in the outer plexiform layer of the turtle retina has been examined by intracellular recordings from L- and C-type horizontal cells in the isolated retina preparation. GABA (1-5 mM) slightly depolarized the L-type horizontal cells, reduced the amplitude of their photoresponses, and slowed down the rate of hyperpolarization during the ON component of the photoresponse. These effects could not be replicated by either muscimol or baclofen. When synaptic transmission from the photoreceptors had been blocked by either kynurenic acid or cobalt ions, GABA depolarized L-type horizontal cells and augmented the remaining photoresponses. Neither muscimol nor baclofen exerted any effect on L-type horizontal cells under these conditions. Nipecotic acid, a competitive inhibitor of the GABA-uptake system, induced effects on turtle L-type horizontal cells which were similar to those exerted by GABA. Thus, the complex GABA effect on turtle L-type horizontal cells seems to represent the summation of at least two actions; an indirect one mediated by the red cones via GABAa-type receptors and a direct one which probably reflects the activation of an electrogenic GABA-uptake system. GABA (1-5 mM) induced a transient depolarization in C-type horizontal cells but eliminated color opponency in only three cells out of seven studied. This observation is inconsistent with the notion that the only neural mechanism responsible for the chromatic properties of C-type horizontal cells in the turtle retina is a GABAergic negative feedback from the L-type horizontal cells onto the green ones.

Animals↗
PubMed1989

An odyssey of the green sea turtle: Ascension Island revisited.

Green turtles (Chelonia mydas) that nest on Ascension Island, in the south-central Atlantic, utilize feeding grounds along the coast of Brazil, more than 2000 km away. To account for the origins of this remarkable migratory behavior, Carr and Coleman [Carr, A. & Coleman, P. J. (1974) Nature (London) 249, 128-130] proposed a vicariant biogeographic scenario involving plate tectonics and natal homing. Under the Carr-Coleman hypothesis, the ancestors of Ascension Island green turtles nested on islands adjacent to South America in the late Cretaceous, soon after the opening of the equatorial Atlantic Ocean. Over the last 70 million years, these volcanic islands have been displaced from South America by sea-floor spreading, at a rate of about 2 cm/year. A population-specific instinct to migrate to Ascension Island is thus proposed to have evolved gradually over tens of millions of years of genetic isolation. Here we critically test the Carr-Coleman hypothesis by assaying genetic divergence among several widely separated green turtle rookeries. We have found fixed or nearly fixed mitochondrial DNA (mtDNA) restriction site differences between some Atlantic rookeries, suggesting a severe restriction on contemporary gene flow. Data are consistent with a natal homing hypothesis. However, an extremely close similarity in overall mtDNA sequences of surveyed Atlantic green turtles from three rookeries is incompatible with the Carr-Coleman scenario. The colonization of Ascension Island, or at least extensive gene flow into the population, has been evolutionarily recent.

Journal Article↗
PubMed1994

ACQUISITION OF MAGNETIC DIRECTIONAL PREFERENCE IN HATCHLING LOGGERHEAD SEA TURTLES

During their natal migration, hatchling loggerhead sea turtles (Caretta caretta L.) establish courses towards the open ocean and maintain them after swimming beyond sight of land. Laboratory experiments have demonstrated that swimming hatchlings can orient using the earth's magnetic field. For the magnetic compass to function in guiding the offshore migration, however, hatchlings must inherit or acquire a magnetic directional preference that reliably leads them towards the open sea. On land, hatchlings find the ocean using light cues associated with the seaward horizon. To determine whether turtles might acquire a preference for a specific magnetic direction on the basis of such cues, we studied the magnetic orientation of turtles initially exposed to light from either magnetic east or west. Hatchlings that had been exposed to light in the east subsequently oriented eastward when tested in darkness, whereas those that had been exposed to light in the west swam westward. Reversing the magnetic field resulted in a corresponding shift in orientation, indicating that the turtles were orienting to the ambient magnetic field. These results demonstrate that light cues can set the preferred direction of magnetic orientation by loggerhead hatchlings. We therefore hypothesize that hatchlings initially establish a seaward course using visual cues available on or near land, then maintain the course using magnetic cues as they migrate into the open sea.

Journal Article↗
PubMed1994

DETECTION OF MAGNETIC INCLINATION ANGLE BY SEA TURTLES: A POSSIBLE MECHANISM FOR DETERMINING LATITUDE

For animals that migrate long distances, the magnetic field of the earth provides not only a possible cue for compass orientation, but a potential source of world-wide positional information. At each location on the globe, the geomagnetic field lines intersect the earth's surface at a specific angle of inclination. Because inclination angles vary with latitude, an animal able to distinguish between different field inclinations might, in principle, determine its approximate latitude. Such an ability, however, has never been demonstrated in any animal. We studied the magnetic orientation behavior of hatchling loggerhead sea turtles (Caretta caretta L.) exposed to earth-strength magnetic fields of different inclinations. Hatchlings exposed to the natural field of their natal beach swam eastward, as they normally do during their offshore migration. In contrast, those subjected to an inclination angle found on the northern boundary of the North Atlantic gyre (their presumed migratory path) swam south-southwest. Hatchlings exposed to an inclination angle found near the southern boundary of the gyre swam in a northeasterly direction, and those exposed to inclination angles they do not normally encounter, or to a field inclination found well within the northern and southern extremes of the gyre, were not significantly oriented. These results demonstrate that sea turtles can distinguish between different magnetic inclination angles and perhaps derive from them an approximation of latitude. Most sea turtles nest on coastlines that are aligned approximately north­south, so that each region of nesting beach has a unique inclination angle associated with it. We therefore hypothesize that the ability to recognize specific inclination angles may largely explain how adult sea turtles can identify their natal beaches after years at sea.

Journal Article↗
PubMed1996

Pinpointing 'Isla Meta': the case of sea turtles and albatrosses

Satellite tracking has recently shown that the very long open-sea journeys of sea turtles and albatrosses share several features, in spite of the different physiological and environmental constraints to which turtles and birds are subjected. The reviews of data obtained by tracking migration and feeding routes show that both sea turtles and albatrosses are able (i) to pinpoint small, isolated targets by following straight courses, (ii) to continue on a bearing at night even when the moon is not visible, (iii) to compensate for wind or current drift and (iv) to return home after experimental, long-distance displacements. Sea turtles and albatrosses seem to rely on a position-fixing capacity which cannot be explained by known navigational mechanisms but might be shared by other animals that display similar feats of open-sea guidance. Future research will further benefit from satellite telemetry and other new techniques applied to experimental investigations.

Journal Article↗
PubMed1999

CO2 excretion and postcapillary pH equilibration in blood-perfused turtle lungs

Turtles possess a significant postcapillary CO2 partial pressure (PCO2) disequilibrium between arterial blood and alveolar gas. There are several possible explanations for this blood disequilibrium including a slow rate of erythrocyte physiological anion shift (Cl-/HCO3- exchange) or inaccessibility of plasma HCO3- to red blood cell or pulmonary carbonic anhydrase. The present study characterized the contribution of erythrocyte anion exchange and pulmonary and erythrocyte carbonic anhydrase to CO2 excretion and, hence, to postcapillary CO2-HCO3--H+ equilibration in blood-perfused turtle (Pseudemys scripta) lungs. Turtle lungs perfused in situ with red cell suspensions containing inhibitors of erythrocyte anion exchange and/or pulmonary and red cell carbonic anhydrase produced significant postcapillary blood PCO2 and pH disequilibria, while no disequilibria were measured when lungs were perfused with control red cell suspensions. Erythrocyte anion exchange and pulmonary intravascular carbonic anhydrase contributed 11 % and 9 %, respectively, to CO2 excretion during single-pass perfusion, whereas red cell and pulmonary carbonic anhydrase contributed 32 % to the measured CO2 excretion. The lack of a measurable PCO2 disequilibrium during perfusion with control erythrocyte suspensions in this study suggests that alternative mechanisms may be responsible for the arterial-lung PCO2 disequilibrium measured during breathing or diving episodes in turtles.

Journal Article↗
PubMed2006

[Clinical observation on treatment of cervicogenic headache with turtle-probing needling at Tianzhu (BL 10)].

OBJECTIVE: To observe therapeutic effect of turtle-probing needling at Tianzhu (BL 10) on cervicogenic headache. METHODS: Seventy cases were randomly divided into a treatment group (n=36) and a control group (n= 34). The treatment group were treated with turtle-probing needling at Tianzhu (BL 10) on the affected side, first perpendicularly needling the point and then penetration-needling homolateral Fengchi (GB 20), Fengfu (GV 16), below cervical Jiaji points (EX-B2), and occipital tuberosity in order. And the control group were treated with acupuncture at Fengchi (GB 20),Tianzhu (BL 10), Shuaigu (GB 8), Touwei (ST 8) and corresponding cervical Jiaji points (EX-B2), Houxi (SI 3), Ashi points at the affected side with routine needling manipulation. Treatment was given once each day, 6 sessions constituting one course. RESULTS: There was no significant difference between the two groups in therapeutic effect (P > 0.05), but the cured and markedly effective rates for analgesic effect in the observation group at the first three sessions were higher than those in the control group (P < 0.05). CONCLUSION: The turtle-probing needling method and the routine needling have a similar therapeutic effect, but the turtle-probing needling method more rapidly produces the analgesic effect.

Acupuncture Points↗
PubMed1997

Synaptic inputs to identified color-coded amacrine and ganglion cells in the turtle retina.

Previous studies have proposed models of the specific synaptic circuitry responsible for color processing in the turtle retina. To determine the accuracy of these models of the circuits underlying color opponency in the inner retina of the turtle (Pseudemys scripta), we have studied the physiology, morphology, and synaptic connectivity of identified amacrine and ganglion cells. These cells were first characterized electrophysiologically and were then stained with horseradish peroxidase. Postembedding electron immunocytochemistry for gamma-aminobutyric acid (GABA) and glycine was used to reveal the neurochemical identity of their synaptic inputs. The red-ON/green, blue-OFF small-field ganglion cell, classified as G24, branched primarily in strata S1, S4, and S5 of the inner plexiform layer (IPL). Ganglion cell G24 showed a complex receptive field organized into a red-ON center surrounded by an inhibitory region, which, in turn, was surrounded by a second excitatory region. Only the center responses were color opponent. The red-OFF/green, blue-ON large-field, stellate amacrine cell, classified as A23b, stratified exclusively in stratum S2, near the S2/S3 border. The color-coded center was surrounded by a luminosity, red-sensitive surround. Synaptic input to G24 and A23b was dominated by amacrine cells (89% and 87%, respectively). G24 received significant input from amacrine cell profiles with GABA (13% of total) as well as glycine (11% of total) immunoreactivity, mostly in the proximal stratum S5 of the IPL (64% and 67% of the total GABA- and glycine-immunoreactive input, respectively). Bipolar cell synaptic input was also found predominantly in S4 and S5 (89%). In contrast, we found no glycine-immunoreactive input to A23b, and the density of the GABA-immunoreactive amacrine cell synaptic input revealed a central (15%) to peripheral (3%) gradient within the dendritic tree. The results of the present study support the previous models of the synaptic circuitry responsible for color-opponent signal processing in the inner retina of the turtle.

Animals↗
PubMed2000

Physiology of common map turtles (Graptemys geographica) hibernating in the Lamoille river, Vermont.

Common map turtles (Graptemys geographica) were collected from a natural underwater hibernaculum in Vermont at monthly intervals during the winter of 1997-1998. Blood was sampled by cardiac puncture and analyzed for pH, PCO(2), PO(2), and hematocrit; separated plasma was tested for Na(+), K(+), Cl(-), total [Ca], total [Mg], [lactate], and osmolality (mOsm kg(-1) H(2)O). Control (eupneic; 1 degrees C) values for pH, PO(2), PCO(2), [HCO(3)(-)], and [lactate] were 7.98 +/- 0.03, 47.4 +/- 18.7, 10.1 +/- 0.7 (mm Hg), 36.1 +/- 0.2 (mmol liter(-1)), and 2.1 +/- 0.1 (mmol liter(-1)), respectively. Between November 1997 and March 1998, ice covered the river and the turtles rested on the substratum, fully exposed to the water, and were apneic. Blood PO(2) was maintained at less than 3 mm Hg (range 0.9 +/- 0.2 to 2.1 +/- 0.7 mm Hg), PCO(2) decreased slightly, plasma [lactate] was <5 mmol liter(-1), and plasma [HCO(3)(-)] decreased significantly. In March [lactate] rose to 7.5 +/- 1.5 mmol liter(-l), but there was no acidemia. Map turtles meet most of their metabolic demand for O(2) via aquatic respiration and tolerate prolonged submergence at 1 degrees C with little change in acid-base or ionic status. The adaptive significance of remaining essentially aerobic during winter is to avoid the life-threatening progressive acidosis that results from anaerobic metabolism. J. Exp. Zool. 286:143-148, 2000.

Animals↗
PubMed2000

Pretectal connections in turtles with special reference to the visual thalamic centers: a hodological and gamma-aminobutyric acid-immunohistochemical study.

Projections of the pretectal region to forebrain and midbrain structures were examined in two species of turtles (Testudo horsfieldi and Emys orbicularis) by axonal tracing and immunocytochemical methods. Two ascending gamma-aminobutyric acid (GABA)ergic pathways to thalamic visual centers were revealed: a weak projection from the retinorecipient nucleus lentiformis mesencephali to the ipsilateral nucleus geniculatus lateralis pars dorsalis and a considerably stronger projection from the nonretinorecipient nucleus pretectalis ventralis to the nucleus rotundus. The latter is primarily ipsilateral, with a weak contralateral component. The interstitial nucleus of the tectothalamic tract is also involved in reciprocal projections of the pretectum and nucleus rotundus. In addition, the pretectal nuclei project reciprocally to the optic tectum and possibly to the telencephalic isocortical homologues. Comparison of these findings with previous work on other species reveals striking similarities between the pretectorotundal pathway in turtles and birds and in the pretectogeniculate pathway in turtles, birds, and mammals.

Animals↗
PubMed1979

The cochlear nuclei of some turtles.

Histological sections of the brains of eight species of turtles representing six different families were studied in order to delineate the cochlear nuclei. In addition, the posterior eighth cranial nerve root and its ganglion were sectioned in 15 specimens of Kinosternon leucostomum, and the distribution of the degenerated nerve fibers and terminals was determined. Two primary and one probably secondary nuclei were demonstrated by the terminal degeneration pattern of the cochlear fibers. A spherical nucleus angularis and an elongated nuclus magnocellularis together form a column of primary cochlear nuclei in the dorsal alar lamina of the medulla. Heavy terminal degeneration is seen associated with these cells following transection of the posterior eighth nerve and ganglion. Nucleus magnocellularis is probably homologous with the nucleus magnocellularis medialis of lizards and crocodiles, and has been described in turtles as nucleus dorsalis magnocellularis by previous authors. A probably secondary cochlear nucleus, nucleus laminaris, lies just ventral to the nucleus magnocellularis. It is associated with the nucleus magnocellularis throughout its length but is shorter. Nucleus laminaris remains free of terminal degeneration after destruction of the posterior eighth nerve and ganglion. The cochlear nuclei of other turtle species were very similar to those of Kinosternon leucostomum.

Animals↗
PubMed1980

The thalamocortical projection in Pseudemys turtles: a quantitative electron microscopic study.

Thalamic fibers in the cortex of Pseudemys turtles were studied with the electron microscope to determine the type of synaptic vesicle they contain, the type of membrane differentiation they form, and the type of processes they contact. Following unilateral removal of the thalamus, all degenerating thalamic axon terminals are located in the outer third of the molecular layer in the rostral half of general cortex. In the middle of this zone they constitute as much as 25% of all vesicle-containing profiles. The degenerated terminals appear as electron opaque profiles, most commonly with a uniform opacity. They contain round agranular vesicles and form synapses with asymmetrical membrane differentiations. They synapse mainly on dendritic spines containing mitochondria and/or membranous sacs, although some thalamic fibers contact small clear spines, dendrites, and, rarely, cell bodies. Counts show that 86% of degenerated contacts are on dendritic spines and 14% on dendritic shafts. The spines probably all belong to the dendrites of the pyramidal cells, whose somata are located in the deep cellular layer. The dendritic shafts and somata are most likely those of the aspinous stellate neurons located in the molecular layer. Although these stellate cells are not sufficiently numerous to form a cell "layer," each transverse section through thalamic recipient cortex contains about nine of these cells and they occur in a ratio of 1:37 to pyramidal cells in the underlying main cell layer. We have calculated that in a rectangular solid of turtle cortex whose dimensions are 1 mm X 1 mm X the depth from pial surface to the underlying ventricle, there are 5.2 million thalamic fiber contacts (all in the outer 100 micrometers), 15,000 pyramidal neurons in the main cell layer, and 400 stellate cells in the molecular layer. Of the 5.2 million thalamic synapses, 0.7 million contact stellate cells and 4.5 million contact pyramidal cells. Thus each stellate cell in the molecular layer receives on the average 1,800 thalamic fiber contacts, while each pyramidal cell receives only 300 thalamic fiber synapses on the distal portion of its dendrites. The calculations lead to the conclusion that individual stellate cells receive at least six times more thalamic fiber synapses than individual pyramidal cells in turtle cortex. We suggest that the stellate cells in the thalamic input zone are inhibitory and that each thalamic volley not only excites efferent pyramidal cells but is also a powerful activator of inhibitory interneurons.

Afferent Pathways↗
PubMed1981

An ultrastructural and biochemical analysis of norepinephrine-containing varicosities in the cerebral cortex of the turtle Pseudemys.

The fine structure and norepinephrine content of small granular vesicle-containing profiles were studied in normal and norepinephrine-depleted cerebral cortex of the turtle, Pseudemys. The cortex was fixed for electron microscopy with the KMnO4 procedure of Koda and Bloom ('77), while the norepinephrine content was assayed wit the radioenzymatic method of Coyle and Henry ('73). Green fluorescent fibers have been described by Parent and Poitras ('74) as located almost exclusively in the outer half of the molecular layer in turtle cortex. Small granular vesicle-containing profiles are found down to 100 microns below the pial surface, but over 50% lie within 20 microns of the surface. Within the outer 100 microns of cortex, the frequency of labeled varicosities is 1.39/1,000 microns2. The average area of the norepinephrine-containing varicosities is 0.61 microns2, and there is a mean of 18.4 vesicles per single section. The average number of large plus small vesicles in an entire varicosity was estimated to be 72. Synaptic membranes are not well-preserved with KMnO4 fixation, but good examples were found of small granular vesicle-containing profiles forming both symmetrical and asymmetrical membrane differentiations. Only a small percentage of the small granular vesicle profiles were associated with a synaptic membrane differentiation in single sections. When norepinephrine-fiber synapses are seen, they usually share a postsynaptic element with another unlabeled vesicle-containing profile. Normal turtle cortex contains an average norepinephrine concentration of 1.95 micrograms/gr, which is about eight times higher than in rat cortex. The ratio of norepinephrine to dopamine is about 18 to one, suggesting that dopamine is present predominantly in a precursor pool for norepinephrine. Small granular vesicle-containing profiles were eliminated after treatment with reserpine and 6-hydroxydopamine in concentrations that were shown to reduce norepinephrine concentration by 94% and 86%, respectively. The labeled varicosities were partially depleted by midbrain hemisection and by an inhibitor of dopamine-beta-hydroxylase (FLA-63). The norepinephrine-containing varicosities are remarkably coextensive with the distribution of thalamic fibers, both in the total extent of cortex where they are found and in the depth of cortex where they terminate. The results support the idea that there is a close structural and functional association between locus coeruleus and thalamic fibers in cerebral cortex, and the apparent difference in frequency of synapses suggests that each fiber system exerts its influence on cortical cells in a different way.

Animals↗
PubMed1984

Morphology of lumbar motoneurons innervating hindlimb muscles in the turtle Pseudemys scripta elegans: an intracellular horseradish peroxidase study.

Motoneurons in the turtle lumbar spinal cord, electrophysiologically identified as innervating a muscle belonging to a functional group, were injected with horseradish peroxidase by electrophoresis. A total of 45 motoneurons were reconstructed from transverse sections. Eleven motoneurons were identified as innervating knee extensor muscles, eight as innervating hip retractor and knee flexor muscles, 14 as supplying ankle and/or toe extensors, and 12 as innervating ankle and/or toe flexor muscles. The cell bodies were elongated and spindle-shaped in the transverse plane. The mean equivalent soma diameter was calculated to be 33.4 micrometers. The mean axon conduction velocity was 15.7 m/second. Significant, though rather weak, positive correlations were found between soma diameter, axon diameter, and axon conduction velocity. The axons of the reconstructed motoneurons did not reveal a recurrent axon collateral. However, a few unidentified motoneurons did possess such collaterals. The dendritic trees were restricted to the ipsilateral side of the cord, but reached out in lateral, ventral, and ventromedial directions to the subpial surface. Easily recognizable and characteristic dendrites were found both in the dorsal dendritic tree and in the dorsomedial dendritic tree. Correlations were calculated between the soma diameter and (1) the number of first-order dendrites, (2) the mean diameter of the first-order dendrites, and (3) the combined diameter of the first-order dendrites. In each case no correlations or only weak correlations were found. Fair correlations were observed between the diameter of a first-order dendrite and the number of terminal dendritic branches (r = .61) and the combined dendritic length (r = .78). However, correlations between the combined diameter of all first-order dendrites per neuron and the total number of terminal dendritic branches and the total combined dendritic length of a neuron were extremely weak. The overall appearance of turtle spinal motoneurons is comparable to that observed in other "lower" vertebrates such as frog and lizard. However, similarities are also observed between certain morphometric parameters in turtle and cat lumbar motoneurons.

Animals↗
PubMed1987

The distribution of proenkephalin-derived peptides in the central nervous system of turtles.

The present study was carried out to examine if peptides similar to the various opioid peptide products of mammalian proenkephalin are present in the turtle central nervous system and to determine their distribution. Antisera against several enkephalin peptides were used: leucine-enkephalin (LENK), methionine-enkephalin (MENK), methionine-enkephalin-arg6-phe7 (MERF), methionine-enkephalin-arg6-gly7-leu8 (MERGL), Peptide E (PEPE), and BAM22P. Their specificity and cross-reactivity were carefully examined. The results indicated that LENK, MENK, and MERF (or highly similar peptides) are present in the turtle central nervous system, and that a peptide showing immunological similarity to BAM22P and PEPE also appeared to be present. In contrast, MERGL did not appear to be present. The distributions of the immunoreactive labeling for LENK, MENK, MERF, BAM22P, and PEPE were indistinguishable, and double-label studies showed that LENK, MERF, and BAM22P were colocalized within individual neurons and fibers. Although all of the above substances were observed in the same cell groups, there was some regional variation, in terms of which enkephalin peptide appeared to be most abundant. The distributions of these enkephalin peptides were very similar to those previously described in mammals and birds. Enkephalin was more abundant in the basal ganglia than in overlying telencephalic regions. Within the basal ganglia, enkephalin was present in striatal neurons and fibers and in pallidal fibers, thereby suggesting the existence of an enkephalinergic striatopallidal projection. Sensory relay nuclei of the thalamus were generally poor in enkephalinergic fibers, whereas the hypothalamus was rich in enkephalinergic neurons and fibers. Enkephalinergic neurons and fibers were present in the midbrain central gray. As is true of neurons of the nucleus spiriformis lateralis of the avian pretectum, the neurons of the homologous cell group in turtles, the dorsal nucleus of the posterior commissure of the pretectum, were found to contain enkephalin and have an enkephalinergic projection to the deep layers of the ipsilateral tectum. Enkephalinergic neurons and fibers were also abundant in the entry zones of the trigeminal nerve and dorsal root fibers of the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Evidence for the inhibitory neurotransmitter gamma-aminobutyric acid in aspiny and sparsely spiny nonpyramidal neurons of the turtle dorsal cortex.

In order to learn more about the anatomical substrate for gamma-aminobutyric acid (GABA)-mediated inhibition in cortical structures, the intrinsic neuronal organization of turtle dorsal cortex was studied by using Golgi impregnation, immunohistochemical localization of GABA and its synthetic enzyme glutamic acid decarboxylase (GAD), and histochemical localization of the presynaptic GABA-degrading enzyme GABA-transaminase (GABA-T). GABAergic markers are found in neurons identical in morphology and distribution to Golgi-impregnated aspiny and sparsely spiny nonpyramidal neurons with locally arborizing axons and appear to label most if not all of the nonpyramidal neurons. In addition, the GABAergic markers are found in punctate structures in a distribution characteristic of presumed inhibitory terminals. The spine-laden pyramidal neurons, the principal projecting cell type in the dorsal cortex, are devoid of labelling for GABAergic markers but are surrounded by presumed GABAergic terminals. The data complement previous physiological and ultrastructural studies that implicate aspiny and sparsely spiny nonpyramidal neurons as mediators of intrinsic inhibition of pyramidal neurons in turtle cortex. The results also suggest similarities in the functional organization of intrinsic inhibitory elements in turtle and mammalian cortex.

4-Aminobutyrate Transaminase↗
PubMed1989

Amacrine and ganglion cells with corticotropin-releasing-factor-like immunoreactivity in the turtle retina.

This study, which uses immunocytochemical methods at the light microscopical, level, examines the cell types in the turtle retina that contain corticotropin-releasing factor (CRF)-like immunoreactivity. Two anatomically distinct amacrine cell types are labeled when antiserum directed against ovine CRF is used to label the turtle retina. These cell types each have a different dendritic arborization pattern and regional distribution. Type A cells are found only in the visual streak and have elongated dendritic arborizations that run parallel to the visual streak. These cells arborize primarily in stratum 1 and near the border of strata 2 and 3, with some processes extending into stratum 5. Type B amacrine cells are found only ventral to the visual streak and arborize primarily in a wide band in strata 4 and 5 with sparse dendritic arborizations in stratum 1. No labeled amacrine cells of any type were found dorsal to the visual streak. The asymmetric dendritic arborizations of the type A amacrine cells and the different regional distributions of the A and B cell types suggest that these two amacrine cell types perform distinct physiological functions. In addition to these labeled amacrine cells, there are also some immunoreactive cell bodies in the ganglion cell layer. Rhodamine crystals were applied to the optic tectum to retrogradely label the ganglion cell bodies. Double label studies indicate that some of the rhodamine-labeled ganglion cells also contain CRF-like immunoreactivity. The localization of CRF-like immunoreactivity in two distinct amacrine cell types and in ganglion cells suggests that it may play multiple roles in visual processing in the turtle retina.

Animals↗
PubMed1990

Organization of the histaminergic system in the brain of the turtle Chinemys reevesii.

To accumulate phylogenetic information on the central histaminergic system, we investigated the histaminergic system in the brain of the Reeves turtle, Chinemys reevesii, using the indirect immunofluorescent method with antiserum against histamine. Histaminergic neuronal cell bodies were found exclusively in the posterior part of the ventral hypothalamus. Histaminergic varicose fibers innervated almost all parts of the turtle brain, but tended to be concentrated in several areas. Very dense innervation was observed in the medial part of the telencephalon, ventrolateral part of the hypothalamus, nucleus habenularis lateralis, and ventromedial part of the tegmentum. Medium density of innervation was seen in the olfactory bulb, nucleus medialis amygdalae, and tectum. Only a few fibers were detected in the lateral part of the telencephalon, dorsal part of the hypothalamus, thalamus, rhombencephalon, and spinal cord. The main ascending fibers were observed in the lateral part of the hypothalamus, sending dense fiber bundles to the cortices dorsomedialis and medialis and nucleus habenularis lateralis. Descending fibers appeared to run in the ventral tegmental area, passing through the dorsal and ventral parts of the midline of the brain stem to the spinal cord. These findings indicate that the general morphological features of the histaminergic system in the turtle brain are similar to those in the mammalian and frog brains.

Animals↗