alpha-Crystallin A sequences of Alligator mississippiensis and the lizard Tupinambis teguixin: molecular evolution and reptilian phylogeny

The amino acid sequences of the eye lens protein alpha-crystallin A from many mammalian and avian species, two frog species, and a dogfish have provided detailed information about the molecular evolution of this protein and allowed some useful inferences about phylogenetic relationships among these species. We now have isolated and sequenced the alpha-crystallins of the American alligator and the common tegu lizard. The reptilian alpha A chains appear to have evolved as slowly as those of other vertebrates, i.e., at two to three amino acid replacements per 100 residues in 100 Myr. The lack of charged replacements and the general types and distribution of replacements also are similar to those in other vertebrate alpha A chains. Maximum-parsimony analyses of the total data set of 67 vertebrate alpha A sequences support the monophyletic origin of alligator, tegu, and birds and favor the grouping of crocodilians and birds as surviving sister groups in the subclass Archosauria.     

Primary and secondary somatosensory projections in direct-developing Plethodontid Salamanders

In three species of plethodontid salamanders (Plethodon jordani, Hydromantes italicus, and Bolitoglossa subpalmata), primary and secondary somatosensory pathways were investigated by means of tract-tracing in vivo and in vitro using biocytin, horseradish peroxidase, and neurobiotin. Afferent sensory fibers of cranial nerves V, VII, and X and the brachial nerve run in the dorsal funiculus of the medulla oblongata and spinal cord. Fibers ascend to the level of, but do not enter, the cerebellum. In the caudal medulla oblongata, sensory tracts of the cranial nerves descend in a dorsal and a dorsolateral bundle and reach the level of the fourth spinal nerve. Two bundles are likewise formed by spinal afferent fibers, which descend to the level of the seventh spinal nerve. Secondary somatosensory projections ascend in contralateral ventral, contralateral lateral, and ipsilateral lateral tracts, the latter two corresponding to the spinal lemniscal tracts of Herrick. These tracts reach the cerebellum, mesencephalic, and diencephalic targets (tegmentum, torus, tectum, tuberculum posterius, pretectum, and ventral thalamus) ipsi- and contra-laterally. The projection to the tectum is confined to fiber layer 4. Fibers of the ascending tracts cross in the cerebellar and tectal commissure. Our study demonstrates that the ascending secondary somatosensory pathways of plethodontid salamanders differ remarkably from those of other amphibians. J. Morphol. 238:307–326, 1998. © 1998 Wiley-Liss, Inc.     

Connections between presumed diencephalic nuclei of the lizard limbic system using horseradish peroxidase axonal transport technique

Connections between the anterior thalamic and habenular nuclei were investigated in the lizard by administering horseradish peroxidase to these nuclei. They were shown to have overlapping locations of afferent sources, namely basotelencephalic structures, nuclei of anterior and hippocampal commissures, preoptic and lateral hypothalamic area, and superior raphe nucleus, as well as common projection zones, viz: the mamillary complex and the ventral tegmental area. Specific connections confined to individual nuclei were discovered, apart from those common to the nuclei: A reciprocal connection with the dorsolateral hypothalamic nucleus (for the anterior dorsolateral nucleus), a projection to the interpeduncular nucleus (for the habenular nucleus), and to the dorsal hypothalamic area (for the dorsomedial nucleus). No sources of afferent pathways to the anterior thalamic nuclei were found in the mamillary complex. All the thalamic nuclei studied, togetherwith their connections, are considered diencephalic relay links in pathways comparable with the dorsal (in the case of the habenular nuclei) and the ventral (with respect to the anterior thalamic nuclei) pathways of the mammalian limbic system.I. M. Sechenov Institute of Evolutionary Physiology and Biochemistry, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 110–120, January–February, 1987.     

Projection of cervical dorsal root fibers to the medulla oblongata in the brush-tailed possum, Trichosurus vulpecula

This study describes the projection of cervical spinal afferent nerve fibers to the medulla in the brush-tailed possum, a marsupial mammal. After single dorsal roots (between C2 and T1) were cut in a series of animals, the Fink-Heimer method was used to demonstrate the projection fields of fibers entering the CNS via specific dorsal roots. In the high cervical spinal cord, afferent fibers from each dorsal root form a discrete layer in the dorsal funiculus. The flattened laminae from upper cervical levels are lateral and those from lower cervical levels are medial within the dorsal columns. All afferent fibers at this level are separated from gray matter by the corticospinal fibers in the dorsal funiculus. All cervical roots project throughout most of the length of the well-developed main cuneate nucleus in a loosely segmentotopic fashion. Fibers from rostral roots enter more lateral parts of the nucleus, and fibers from lower levels pass to more medial areas; but terminal projection fields are typically large and overlap extensively. At more rostral medullary levels, fibers from all cervical dorsal roots also reach the external cuneate nucleus. The spatial arrangement here is more complex and more extensively overlapped than in the cuneate nucleus. Rostral cervical root fibers reach ventral and ventrolateral areas of the external cuneate nucleus and continue to its rostral pole; more caudal root fibers project to more dorsal and medial regions within the nucleus. These results demonstrate that projection patterns of spinal afferents in this marsupial are similar to those seen in the few placental species for which detailed data concerning this system are available.     

Noggin is required for correct guidance of dorsal root ganglion axons

Members of the bone morphogenetic protein family of secreted protein signals have been implicated as axon guidance cues for specific neurons in Caenorhabditis elegans and in mammals. We have examined axonal pathfinding in mice lacking the secreted bone morphogenetic protein antagonist Noggin. We have found defects in projection of several groups of neurons, including the initial ascending projections from the dorsal root ganglia, motor axons innervating the distal forelimb, and cranial nerve VII. The case of the dorsal root ganglion defect is especially interesting: initial projections from the dorsal root ganglion enter the dorsal root entry zone, as normal, but then project directly into the gray matter of the spinal cord, rather than turning rostrally and caudally. Explant experiments suggest that the defect lies within the spinal cord and not the dorsal root ganglion itself. However, exogenous bone morphogenetic proteins are unable to attract or repel these axons, and the spinal cord shows only very subtle alterations in dorsal-ventral pattern in Noggin mutants. We suggest that the defect in projection into the spinal cord is likely the result of bone morphogenetic proteins disrupting the transduction of some unidentified repulsive signal from the spinal cord gray matter.     

Spinocervical Tract-Dorsal Column Postsynaptic Neurons: A Double-Projection Neuronal System

Evidence is presented for the existence of a newly discovered double-projection spinal neuronal system, the spinocervical tract-dorsal column postsynaptic neurons. The neurons are characterized by axonal bifurcation in the cervico-thoracic junction, by branched axons traveling in the dorsal column and the dorsolateral funiculus, and by double projection to the dorsal column nuclei and the lateral cervical nucleus. The neurons, with longitudinally distributed dendritic trees and local axon collaterals, primarily originate in laminae III-V of the dorsal horn and receive innocuous and noxious inputs transmitted along the A-beta primary afferents from the periphery. These neurons are thought to be an intersection of the spinocervical tract and the dorsal column postsynaptic neurons, and to function as a nonlemniscal system in mediation and modulation of ascending sensory information, including pain.     

Spinocervical tract-dorsal column postsynaptic neurons: a double-projection neuronal system

Evidence is presented for the existence of a newly discovered double-projection spinal neuronal system, the spinocervical tract-dorsal column postsynaptic neurons. The neurons are characterized by axonal bifurcation in the cervico-thoracic junction, by branched axons traveling in the dorsal column and the dorsolateral funiculus, and by double projection to the dorsal column nuclei and the lateral cervical nucleus. The neurons, with longitudinally distributed dendritic trees and local axon collaterals, primarily originate in laminae III-V of the dorsal horn and receive innocuous and noxious inputs transmitted along the A-beta primary afferents from the periphery. These neurons are thought to be an intersection of the spinocervical tract and the dorsal column postsynaptic neurons, and to function as a nonlemniscal system in mediation and modulation of ascending sensory information, including pain.     

Terminal distribution of retinal fibers in the tegu lizard (Tupinambis nigropunctatus)

Summary The retinal projections in the tegu lizard were traced using degeneration-silver methods. Bilateral projections were found to the dorsolateral geniculate and the posterodorsal nuclei. Unilateral, crossed projections were traced to the suprachiasmatic nucleus, the ventrolateral geniculate nucleus, the mesencephalic lentiform nucleus, nucleus geniculatus praetectalis, the ectomammillary nucleus, and the optic tectum. Some of these connections are distinctly different from those reported in other reptiles and suggest that important interspecific variations occur among reptiles.     

The distribution and origin of VIP in the spinal cord of six mammalian species

The distribution of VIP-immunoreactivity was studied in the spinal cord and dorsal root ganglia of 6 mammalian species. Immunoreactive fibres and cell bodies were most apparent in the dorsal horn, dorsolateral funiculus, intermediolateral cell columns and the area around the central canal. The distribution of VIP immunoreactivity was similar in all species studied, mouse, rat, guinea pig, cat, horse and the marmoset monkey. There were fewer VIP fibres in the dorsal horn of cervical and thoracic segments than in lumbosacral segments. Using radioimmunoassay this gradient increase was quantitatively most marked in the sacral spinal cord of the cat. In dorsal root ganglia few nerve cell bodies but numerous fibres were present. A dual origin for VIP in the spinal cord is suggested: (A) Extrinsic, from dorsal root afferent fibres since immunoreactivity was decreased in dorsally rhizotomized animals (cats and rats) and in capsaicin pretreated rats (microinjection of dorsal root ganglia). (B) From local cell bodies intrinsic to the spinal cord which became visible after colchicine pretreatment of rats.     

Afferent and efferent components of the facial nerve in a frog,Rana pipiens

Summary The seventh cranial nerve in Rana pipiens is a slender nerve with limited peripheral distribution. We investigated the afferent and efferent components of this nerve by labeling its major branch, the hyomandibular, with horseradish peroxidase. The efferent portion of the seventh nerve originates from a small cell group in the upper medulla which contains two subdivisions. Afferent fibers carried in nerve VII travel in the solitary tract and the dorsolateral funiculus. The solitary component consists of a small number of ascending fibers that reach the level of the trigeminal nucleus and a large descending component that terminates slightly caudal to the obex in the commissural nuclei of the solitary complex. Afferent fibers also descend in the dorsolateral funiculus; many of these fibers cross dorsal to the central canal in the lower medulla. Most of the fibers in the dorsolateral funiculus terminate in the ipsilateral and contralateral dorsal horns and in nuclei of the dorsal column. A few ipsilateral fibers reach lower thoracic levels of the spinal cord.     

The area octavo-lateralis in Xenopus laevis

Summary Central projections of afferents from the lateral line nerves and from the individual branches of the VIIIth cranial nerve in Xenopus laevis and Xenopus mülleri were studied by the application of HRP to the cut end of the nerves.Upon entering the rhombencephalon, the lateral line afferents form a longitudinal fascicle of ascending and descending branches in the ventro-lateral part of the lateral line neuropile. The fascicle exhibits a topographic organization, that is not reflected in the terminal field of the side branches. The terminal field can be subdivided into a rostral, a medial and a caudal part, each of which shows specific branching and terminal pattern of the lateral line afferents. These different patterns within the terminal field are interpreted as the reflection of functional subdivisions of the lateral line area. The study did not reveal a simple topographic relationship between peripheral neuromasts and their central projections.Two nuclei of the alar plate with significant lateral line input were delineated: the lateral line nucleus (LLN) and the medial part of the anterior nucleus (AN). An additional cell group, the intermediate nucleus (IN), is a zone of lateral line and eighth nerve overlap, although such zones also exist within the ventral part of the LLN and the dorsal part of the caudal nucleus (CN). Six nuclei which receive significant VIIIth nerve input are recognized: the cerebellar nucleus (CbN), the lateral part of the anterior nucleus, the dorsal medullary nucleus (DMN), the lateral octavus nucleus (LON), the medial vestibular nucleus (MVN) and the caudal nucleus (CN).All inner ear organs have more than one projection field. All organs project to the dorsal part of the LON and the lateral part of the AN. Lagena, amphibian papilla and basilar papilla project to separate regions of the dorsal medullary nucleus (DMN). There is evidence for a topographic relation between the hair cells of the amphibian papilla (AP) and the central projections of AP fibers. The sacculus projects extensively to a region between the DMN and the LON. Fibers from the sacculus and the lagena project directly to the superior olive. Fibers from the utriculus and the three crista organs terminate predominantly in the medial vestibular nucleus (MVN) and in the adjacent parts of the reticular formation, and their terminal structures appear to be organotopically organised. Octavus fiber projections to the cerebellum and to the spinal cord are also described.     

Deleterious Mutations of a Claw Keratin in Multiple Taxa of Reptiles

We have recently shown that homologs of mammalian hair keratins are expressed in the claws of the green anole lizard, Anolis carolinensis. To test whether reptilian hair keratin homologs are functionally associated with claws, we investigated the conservation of the prototypical reptilian hair keratin homolog, hard acidic keratin 1 (HA1), in representative species from all main clades of reptiles. A complete cDNA of HA1 was cloned from the claw-forming epidermis of the lacertid lizard Podarcis sicula, and partial HA1 gene sequences could be amplified from genomic DNA of tuatara, lizards, gekkos, turtles, and crocodiles. In contrast, the HA1 gene of the limbless slow worm, Anguis fragilis, and of two species of turtles contained at least one deleterious mutation. Moreover, an HA1 gene was undetectable in the softshell turtle, snakes, and birds. Mapping the presence and absence of HA1 onto the phylogenetic tree of sauropsids suggested that the HA1 gene has been lost independently in several lineages of reptiles. The species distribution of HA1 is compatible with the hypothesis of a primary function of HA1 in claws but also shows that the formation of reptilian claws does not strictly depend on this keratin.     

Arrangement and innervation of the iliocostalis and longissimus muscles of the brown caiman (Caiman crocodilus fuscus: Alligatoridae, Crocodilia).

The axial musculature of the brown caiman was investigated in detail with particular attention to the nerve supply, using a binocular stereomicroscope. Due to the prominent development of the longissimus (Lo) and the iliocostalis (IC) muscles of the caiman, the pattern of distribution of the spinal nerves in the body wall was unique; there also was less differentiation of the external intercostalis. There were four primary divisions of the spinal nerves in the thoracic region of the caiman, from ventral to dorsal: the intercostal nerve, the IC nerve, the Lo nerve, and the dorsal main trunk. Thus, the classic concept of the organization of the spinal nerves may not be suitable for the caiman. These findings suggest that evolutionary changes in the dorsolateral axial musculature have brought about the rearrangement of the organization of the spinal nerves. In addition, each clearly segmented myotome of the Lo and IC was innervated by more than two segments of the spinal nerves (plurisegmental innervation). The manner of formation of the myotome and its innervation is discussed from the viewpoint of comparative and developmental anatomy.     

Thalamic nociceptive systems

A role for thalamic structures in the processing of signals of nociception and pain has been suggested on the basis of clinical data since the turn of the century. Searches for a 'pain centre' by lesion or stimulation were often disappointing and the electrophysiological data were rare and usually contradictory. However, recent electrophysiological anatomical and neuropharmacological studies, made in various species (mainly rat and monkey) appear now progressively to give some clues in the understanding of pain process at the thalamic level. These studies have been mainly concerned with the areas receiving projections from ascending spinal pathways conveying noxious inputs, either directly by the spinothalamic tract or indirectly by the spinoreticulothalamic pathway. The eventual respective roles of these thalamic structures are considered. Electrophysiological recordings from thalamic structures in a model of experimental pain, arthritic rats, are also presented.     

The functional anatomy of the basal ganglia of birds.

To study how the basal ganglia can control movement in birds, we have reinvestigated the connections of the pigeon dorsal pallidum. Our results indicate that avian basal ganglia appear to control movement through major projections to several premotor pretectal and tegmental centres which innervate the tectum, and through a minor projection to a possible motor thalamic centre which innervates the Wulst. For such control, separate striatopallidal output circuits appear to exist in birds that are remarkably similar to those described in mammals, suggesting that avian and mammalian basal ganglia may control movement through similar mechanisms, and that the morphological substrate for such control evolved earlier than previously thought.     

Developmental changes in the expression level of connexin36 in the rat retina

Many noctuid moth species perceive ultrasound via tympanic ears that are located at the metathorax. Whereas the neural processing of auditory information is well studied at the peripheral and first synaptic level, little is known about the features characterizing higher order sound-sensitive neurons in the moth brain. During intracellular recordings from the lateral protocerebrum in the brain of three noctuid moth species, Heliothis virescens, Helicoverpa armigera and Helicoverpa assulta, we found an assembly of neurons responding to transient sound pulses of broad bandwidth. The majority of the auditory neurons ascended from the ventral cord and ramified densely within the anterior region of the ventro-lateral protocerebrum. The physiological and morphological characteristics of these auditory neurons were similar. We detected one additional sound-sensitive neuron, a brain interneuron with its soma positioned near the calyces of mushroom bodies and with numerous neuronal processes in the ventro-lateral protocerebrum. Mass-staining of ventral-cord neurons supported the assumption that the ventro-lateral region of the moth brain was the main target for the auditory projections ascending from the ventral cord.     

Nitric oxide synthase in the spinal cord of the frog, Xenopus laevis

The expression of nitric oxide synthase was investigated in the spinal cord of the South African clawed frog by NADPH diaphorase histochemistry and immunohistochemistry. The dorsal field contained many strongly positive neurons and a dense plexus of processes. Only few nitric oxide synthase-positive cells occurred in the lateral and central field. Motoneurons were negative. A dense accumulation of stained neurons was located dorsal and dorsomedial to the motoneurons. The white matter harbored many positive fibers. These were most abundant in the dorsal funiculus, and obviously consist of nonprimary projections to the brainstem. These results suggest that nitric oxide represents a widely used messenger molecule in the frog spinal cord, in particular with respect to the processing of sensory information.