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.     

Ultrastructure of the tastebuds of the red-eared turtle,Chrysemys scripta elegans

The fine structure of the turtle tastebud has been examined by light, transmission, and scanning electron microscopy. It contains five types of cells on the basis of their cytological features, designated types 1,2,3,A, and B. Types 1, 2, and 3 reach the taste pore, whereas types A and B are located basally. The type 2 cell has access to the tongue surface, i.e., the site of gustatory stimuli, and also synapses onto afferent nerves; it probably is a gustatory receptor cell and corresponds to the so-called “light” cell observed in other vertebrate tastebuds. Some cells may be differentiating. In support of this hypothesis, light microscopic autoradiography shows that postmitotic cells occur in the tastebuds within 24 hours after administration of H³-thymidine. The tastebuds of the turtle are similar to those of other vertebrates described electron-microscopically.     

Interactions between tectal radial cells in the red-eared turtle, Pseudemys scripta elegans: an analysis of tectal modules.

The optic tectum is a major subdivision of the visual system in reptiles. Previous studies have characterized the laminar pattern, the neuronal populations, and the afferent and efferent connections of the optic tectum in a variety of reptiles. However, little is known about the interactions that occur between neurons within the tectum. This study describes two kinds of interactions that occur between one major class of neurons, the radial cells, in the optic tectum of Pseudemys using Nissl, Golgi and electron microscopic preparations. Radial cells have somata which bear long, radially oriented apical dendrites from their upper poles and short, basal dendrites from their lower poles. They are divided into two populations on the basis of the distribution of their somata in the tectum. Deep radial cells have somata densely packed in the stratum griseum periventriculare. Their plasma membranes form casual appositions. Middle radial cells have somata scattered throughout the stratum griseum centrale and stratum fibrosum et griseum superficiale and do not contact each other. The apical dendrites of both populations of radial cells participate in vertically oriented, dendritic bundles. The plasma membranes of the dendrites in these bundles form casual appositions in the deeper tectal layers and chemical, dendrodenritic synapses within the stratum fibrosum et griseum superficiale. The synapses have clear, round synaptic vesicles and slightly asymmetric membrane densities. Thus, radial cells interact via both casual appositions and chemical synapses. These interactions suggest that radial cells may form a basic framework in the tectum. Because both populations of radial cells extend into the stratum fibrosum et griseum superficiale and stratum opticum, they may receive input from some of the same tectal afferent systems. Because the deep radial cells alone have somata and dendrites in the deep tectal layers, they may receive additional inputs that the middle radial cells do not. Neurons in the two populations interact via chemical dendrodentritic synapses, thereby forming vertically oriented modules in the tectum.     

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.     

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.     

Regeneration of the eighth nerve fibers after transection in the red-eared turtle,Chrysemys scripta elegans

The present study examined the time sequence of degeneration and regeneration after transection of the eighth nerve in the red-eared turtle as well as the chromatolytic reaction of the turtle auditory ganglion cells. Horseradish peroxidase (HRP) transport between auditory ganglion cells and the medulla identified eighth nerve connections. The course of eighth nerve degeneration was followed with Fink and Heimer degeneration stain and HRP reaction. Cresyl-violet-stained sections through auditory ganglion cells were observed for chromatolysis. Degeneration by-product was intense in the eighth nerve and primary auditory nuclei in turtles surviving 25 and 32 days after eighth nerve transection. Turtles surviving 45 days or less after eighth nerve transection showed HRP reaction product in the eighth nerve to the point of its dorsolateral penetration into the medulla following cochlear duct injections. Acoustic tubercle injections in 50-day survivors showed HRP filling in eighth nerve and auditory ganglion cells. Cochlear duct injections in 67-day survivors demonstrated HRP filling in the eighth nerve and acoustic tubercle. Sections stained for degeneration in 67-day survivors showed little or no degeneration by-product and 80- and 90-day survivors showed none. The proportion of chromatolytic auditory ganglion cells was greatest in the 50-day postoperative turtles when compared to control turtles and other survival stages. Animals which survived longer than 50 days had reduced numbers of chromatolytic cells. Results suggest that the eighth nerve fibers are regenerated to primary brainstem auditory nuclei in experimental turtles surviving 50 days or more. Regeneration occurs between the 45th and 50th day following transection.