The retinopetal system in the turtle Pseudemys scripta elegans

Injections of 125I wheat-germ agglutinin or horseradish peroxidase into the eyes of turtles labeled retrogradely cells in a mesencephalic reticular area lying between the trochlear and the isthmic nuclei. Their number was small and they were found predominantly contralateral to the injected eye. These reticular neurons were not labeled following control injections into the orbital cavity and therefore are considered to project to the retina similar to correspondingly located neurons in some other vertebrates.     

Vascular smooth muscle contractile properties in the turtle Pseudemys scripta elegans

1. Turtle aortic rings were characterized by high frequency spontaneous contractile activity and variable responsiveness to constrictor agents.2. The tissue response was remarkably insensitive to temperature at a range of 37°–15°C.3. The contractile response was effectively blocked by the calcium channel antagonist nifedipine and was substantially dependent on extracellular calcium concentrations.4. Lowering the sodium concentration of the bath medium resulted in a strong, transient contraction followed by reduced responsiveness to norepinephrine and the absence of spontaneous activity.5. Disruption of the vessel endothelium resulted in enhanced and reduced responsiveness to norepinephrine (NE) and acetylcholine (ACh), respectively.6. The results indicate that the regulation of contractile function in turtle vascular smooth muscle differs in several respects from that of mammalian tissue, perhaps, reflecting the adaptation of the vasculature to low pressure and ectothermic conditions.     

Permeability of the urinary bladder of the turtle, Pseudemys scripta elegans, to ammonia

1. The permeability of the isolated turtle urinary bladder to ammonia was investigated by varying the ratio of NH3 to NH4+ concentration in the serosal bath and measuring the flux of ammonia into the mucosal bath. 2. The permeability of the turtle bladder to NH3 was in the range of 5.4-6.1 x 10(-3) cm/sec and the permeability of the unstirred layer to NH4+ was in the range of 1.1-2.1 x 10(-5) cm/sec. 3. The flux of ammonia calculated from the permeability of NH3 can account for the decrease in mucosal H+ secretion observed with addition of NH4Cl to the serosal bath.     

Isolation and structural characterization of insulin, glucagon and somatostatin from the turtle, Pseudemys scripta

The chelonians occupy an important position in phylogeny representing a very early branching from the ancestral reptile stock. Hormonal polypeptides in an extract of the pancreas of the red-eared turtle were purified to homogeneity by reversed phase HPLC and their primary structures were determined. Turtle insulin is identical to chicken insulin. Turtle glucagon differs from chicken glucagon by the substitution of a serine by a threonine residue at position 16 and from mammalian glucagon by an additional substitution of an asparagine by a serine residue at position 28. Turtle pancreatic somatostatin is identical to mammalian somatostatin-14. The crocodilians are phylogenetically much closer to the birds than are the chelonians. Alligator insulin, however, contains three amino acid substitutions relative to chicken insulin. Thus, caution is required when inferring phylogenetic relationships based upon a comparison of amino acid sequences of homologous peptides.     

Immunocytochemical and biochemical studies of histamine in the retina of the turtle Pseudemys scripta

A combination of immunocytochemical and biochemical methods was used to study histamine in the turtle retina. Histamine-like immunoreactivity was localized within paraboloids of certain cone photoreceptors by use of two different antisera directed against histamine. Preincubation of eyecups in Ringer's containing 10 microM histamine selectively increased the immunoreactivity of these photoreceptor paraboloids. The present localization of histamine in paraboloids indicated that, although histamine is in photoreceptors of the turtle retina, it may play some metabolic or neuromodulatory role, and not function as a neurotransmitter.     

Morphology and histochemistry of the ambiens muscle of the red-eared turtle (Pseudemys scripta)

Six fiber types have been described in the ambiens muscle of red-eared turtles. These include one slow oxidative type, two fast oxidative types, two fast oxidative and glycolytic types, and one fast glycolytic type. Fiber types are non-randomly distributed throughout cross sections of the muscle. There is a decreasing gradient of oxidative staining and an increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle. The slow oxidative fibers are predominantly located within one or two fascicles of the superficial surface of the muscle. The fast glycolytic fibers are predominant in deep fascicles. In contrast to previous reports of histochemically monotypic intrafusal fibers in turtle muscle, ambiens muscle spindles have been observed containing one to eleven intrafusal fibers, including two fiber types. Fiber diameter and area are consistently smaller than observed in most extrafusal fibers. Spindles are predominantly located in superficial and cranial fascicles of the ambiens muscle and are located in regions characterized by extrafusal fibers with high oxidative activity.