Changes in the Motor Asymmetry and Structure of Mauthner Neurons of the Goldfish Resulting from Unilateral Visual Deprivation

We studied the effects of unilateral enucleation of the eye on the motor asymmetry of goldfish fries and morphometric characteristics of their Mauthner neurons, MNs (data of 3D reconstruction using serial slices). Enucleation of the right or left eye in ambidextral fishes resulted in stable preference of turnings during swimming toward the side of visual deafferentation and in a shift of the initial motor asymmetry coefficient (MAC) by 25%, on average. Ipsilateral enucleation of the eye in dextral and sinistral fishes intensified the initial motor asymmetry by 20%. Contralateral enucleation of the eye in dextral and sinistral fishes induced inversion of the motor asymmetry with a decrease in the MAC by 50%, on average. All operated fishes stably (within 3 months or more) preferred to turn toward the side of the enucleated eye. Morphological measurements showed that the size of the ventral dendrite of the MN contralateral with respect to the side of enucleation noticeably decreased. At the same time, this neuron (according to a shift in the motor asymmetry of the fish) became the functionally dominant unit. These data agree with the earlier supposition on a reciprocal relation between the level of functional activity of the MN and the size of its ventral dendrite. Selective changes in the dimension of the ventral dendrite of the MN receiving visual inputs probably resulted from the action of some endogenous trophic factor. The effect of this factor was enhanced after enucleation of the eye and the corresponding dysfunction of the contralateral visual input. A specific local change in the balance of neurotransmitter influences upon the MN ventral dendrite can play the role of such a factor. From the neurophysiological aspect, a decrease in the size of the ventral MN dendrite is a primary link in the chain of events resulting in modification of behavior; it leads to intensification of the integral functional activity of the MN and a shift of the motor asymmetry of the fish compensating, in such a way, the effect of unilateral visual deprivation.     

Escape Behaviour: Reciprocal Inhibition Ensures Effective Escape Trajectory

When a zebrafish makes a fast escape response, Mauthner cells directly activate contralateral spinal interneurons which feed reciprocal inhibition to motorneurons on the stimulated side. Ablation of these interneurons in transgenic animals impairs escape responses, indicating their crucial role in survival.     

Morphology of calretinin-immunoreactive neurons in the superficial layers of hamster superior colliculus after enucleation: lack of co-localization with GABA

We recently reported on the distribution and effects of eye enucleation on the immunoreactivity of calretinin in the superficial layers of the hamster superior colliculus (SC). In the present study, we describe the types of labeled cells and compare this labeling to that of GABA, the major inhibitory neurotransmitter in the central nervous system. An almost complete depletion of calretinin-immunoreactive (IR) fibers in the superficial layers of the contralateral SC was found following unilateral enucleation. On the contralateral SC, many calretinin-IR cells were newly appeared. The majority of the newly-appeared cells had small- to medium-sized round, oval, or vertical fusiform cell bodies. Two-color immunofluorescence revealed that none of these newly-appeared cells were labeled with an antibody to GABA. The present results show that the calretinin-IR cells are unique in the superficial hamster SC when compared to most of the other brain areas, where many calretinin-IR cells are GABAergic interneurons.     

Stereotyped and variable growth of redirected Mauthner axons

To assay the axon tract organizing capabilities of different regions of the vertebrate CNS, Mauthner axons were redirected by grafting supernumerary hindbrains in Xenopus embryos. The 63 redirected Mauthner axons thus produced included donor axons projecting into the host CNS and host axons that grew through the graft or that were redirected in the host CNS. Two major phenomena were observed. Caudal to the optic chiasm, the Mauthner axons followed a single ipsilateral stereotyped route—the basal substrate pathway—extending in the ventral and ventrolateral marginal zone from the diencephalon to the caudal spinal cord. In contrast, rostral to the optic chiasm, these same Mauthner axons followed variable ipsilateral and contralateral routes. Even pairs of Mauthner axons entering the optic chiasm side-by-side eventually followed different routes in normal forebrains. The contrasting behaviors of the Mauthner axons growing in the rostral diencephalon and telencephalon and of the same Mauthner axons growing elsewhere suggest that there are differences in the effective guidance cues between these two regions of the developing brain. This is consistent with other types of neuroanatomical and neuroembryological evidence indicating a fundamental division between the rostral and the caudal diencephalon.     

Early locomotor behaviour and the structure of the nervous system in embryos and larvae of the Australian lungfish, Neoceratodusforsteri‡

This paper describes the development of early locomotor responses to mechanical stimulation in the Australian lungfish Neoceralodus and compares them with structural changes in the spinal cord. Initial movements occur spontaneously prior to innervation of myotomal muscles, and are therefore myogenic. After muscle innervation, embryos only move when stimulated; the first type of response to sharp touch is a unilateral flexion away from the stimulus, then at a later stage the contralateral response is followed by a homolateral flexure which, later still, passes into bursts of swimming. The initial contralateral response occurs when decussating interneurons are detectable but before spinal sensory innervation of the trunk; however, the trigeminal sensory pathway has been established by this time and probably mediates the first mechanoreceptive signals from trunk epidermis. Later, Rohon-Beard cells innervate the trunk skin, and then dorsal root neurons take over the major sensory role. The secondary homolateral response and bursts of swimming are paralleled by the development of several types of spinal interneurons and the ingrowth of Mauthner cell axons.     

Decrease in occurrence of fast startle responses after selective Mauthner cell ablation in goldfish (Carassius auratus )

A single action potential in one of a pair of reticulospinal neurons, the Mauthner cells, precedes a short-latency electromyographic response of the trunk and tail musculature on the opposite side of the body and a fast startle response in goldfish. It has been postulated that not only the Mauthner cell, but also an array of neurons can trigger or participate in fast startle responses (Eaton et al. 1991). We have selectively ablated the Mauthner cells in goldfish to study how neurons of the brainstem fast startle response network interact. The probability of eliciting a fast startle response was significantly less in fish with double Mauthner cell ablations, as compared to the responsiveness of control fish. The finding that there is a significant decrease in the occurrence of fast startle responses in animals with no Mauthner cells, implies that the Mauthner cell may play a role in triggering the involvement of the other network elements in fast startle responses. We hypothesize that Mauthner cell activation may be important in bringing those reticulospinal neurons that are “primed” by the behavioral context to threshold and provides the basis for studies focused on the interactive nature of the brainstem startle response network. Accepted: 4 November 1998     

The Neuroprotective Effect of the Thr–Ser–Lys–Tyr Peptide in a Goldfish Mauthner Cell Model in vivo

The effects of the Thr–Ser–Lys–Tyr peptide, which was shown to display neuroprotective activity in cell cultures in vitro, were studied in the model of paired Mauthner cells of goldfish. It was found that intracerebral injections provided the peptide to be applied into the zone of the right Mauthner cell under the fourth ventricle of the hindbrain lead to a dose-dependent decrease in the number of spontaneous turns of the goldfish to the left. It was shown that this effect is not eliminated under long-lasting optokinetic stimulation when the fish instinctively follow stimuli with a low spatial frequency that are moving in the nasal-to-temporal direction. We used the method of three-dimensional reconstruction by serial histological sections to study the dendrite morphology of the Mauthner cells in control and experimental goldfish. It was found that optokinetic stimulation of control goldfish evokes the dystrophy of the ventral dendrite of the right Mauthner cell, which is the target of this type of stimulation. Conversely, the peptide stabilize the size of the ventral dendrite of the right Mauthner cell under stimulation. These data could be interpreted as evidence of the neuroprotective effect of the Thr–Ser–Lys–Tyr peptide in vivo.     

Mauthner cell-evoked synaptic actions on pacemaker medullary neurons of a weakly electric fish

The present study was designed to examine the synaptic events in neurons of the pacemaker nucleus of Gymnotus carapo during the increase in rate of the electric organ discharge following activation of Mauthner cells. Pacemaker and relay cells were investigated using intracellular recordings which were performed under two different conditions: (1) with the pacemaker nucleus spontaneously discharging and (2) after its activity was abolished by anesthesia. Mauthner axon activation induced an increase in the rate of pacemaker cell discharges. This response was accompanied by an increase in the slope of the pacemaker potential (up to 110%) and a depolarization of these cells. The discharges of relay cells followed one to one those of pacemaker cells. In contrast to that observed in pacemaker cells, only brief depolarizing antidromic effects could be evoked in relay cells after Mauthner axon activation. In quiescent pacemaker cells, Mauthner cell activation induced a prolonged (up to 500 ms) depolarizing potential with an average amplitude of 1.92 ± 0.82 mV; its latency was 4.43 ± 1.14 ms. Our data indicate that, within the pacemaker nucleus, the population of pacemaker cells is the only target for Mauthner cell-evoked, short-latency excitatory synaptic actions. Accepted: 1 March 1997     

Release of Endogenous Amino Acids from Superior Colliculus of the Rabbit: In Vitro Studies After Retinal Ablation

Tissue slices from the superior colliculi (SC) of the rabbit were superfused and investigated 1 week after unilateral eye removal. Amino acid levels were determined both in the tissue slices and in the medium after chemical depolarisation (56 mM K). The amino acid determinations were done fluorimetrically by precolumn derivation and HPLC separation. Colliculi contralateral to the enucleation exhibited a 16% reduction in glutamate compared with the ipsilateral colliculi. The Ca-dependent release of glutamate or other amino acids tested was not appreciably affected by enucleation. However, both the total and the Ca-independent release of glutamate was lower from contralateral SC slices compared with the ipsilateral slices. The results do not favour glutamate as the major optic nerve transmitter in the rabbit, but do not rule out glutamate as a transmitter in a minor population of retinal fibres.     

Analysis of chlorophyll fluorescence reveals stage specific patterns of chloroplast-containing cells during Arabidopsis embryogenesis

The basic body plan of a plant is established early in embryogenesis when cells differentiate, giving rise to the apical and basal regions of the embryo. Using chlorophyll fluorescence as a marker for chloroplasts, we have detected specific patterns of chloroplast-containing cells at specific stages of embryogenesis. Non-randomly distributed chloroplast-containing cells are seen as early as the globular stage of embryogenesis in Arabidopsis. In the heart stage of embryogenesis, chloroplast containing cells are detected in epidermal cells as well as a central region of the heart stage embryo, forming a triangular septum of chloroplast-containing cells that divides the embryo into three equal sectors. Torpedo stage embryos have chloroplast-containing epidermal cells and a central band of chloroplast-containing cells in the cortex layer, just below the shoot apical meristem. In the walking-stick stage of embryogenesis, chloroplasts are present in the epidermal, cortex and endodermal cells. The chloroplasts appear reduced or absent from the provascular and columella cells of walking-stick stage embryos. These results suggest that there is a tight regulation of plastid differentiation during embryogenesis that generates specific patterns of chloroplast-containing cells in specific cell layers at specific stages of embryogenesis.     

Influence of diazepam on regenerating adrenal cortex in Wistar rats

The influence of diazepam on the mitotic activity of regenerating adrenal cortex in male Wistar rats was investigated. Diazepam administration (5 mg/kg/day) was shown to inhibit the mitotic index of adrenocortical cells on the 4th and 8th day after adrenal enucleation combined with contralateral adrenalectomy. The possible mechanism of diazepam action is discussed.     

The role of tissue expanders in an anophthalmic animal model

A study of orbital bony expansion using a custom tissue expander was performed in the anophthalmic cat model. Twelve 6-week-old kittens underwent right unilateral enucleations. Six kittens had immediate insertion of a tissue expander into the orbit. The remaining six served as controls. Every 2 weeks 0.5 cc saline was injected into the expander to a maximum of 5 cc. External horizontal and vertical orbital dimensions were obtained by palpation technique weekly. All animals had preoperative and study conclusion head CT scans with three-dimensional reconstructions performed. Dry skull preparations were done at the study conclusion at 24 weeks. Results demonstrated that tissue expanders were successful in maintaining normal orbital growth and size relative to the contralateral control orbit. The animals with enucleation only had an average difference in vertical and horizontal orbital measurements of -27 and -13 percent when compared with the contralateral normal orbit. In contrast, the enucleation and tissue-expansion animals had vertical and horizontal measurements of +4 and +2 percent (p less than 0.05) when compared with the contralateral orbit. Head CT scans with three-dimensional reconstructions demonstrated normal orbital geometry and volume for the animals with tissue expanders, whereas animals with enucleation only had small hypoplastic orbits. In conclusion, orbital tissue expanders offer a promising new technique in the treatment of anophthalmos.     

Specific reduction of development of the Mauthner neuron lateral dendrite after otic capsule ablation in Brachydanio rerio

During development, afferent fibers may stimulate development of postsynaptic target neurons. By surgically ablating an otic vesicle in zebrafish embryos 30 hr after fertilization we deprived the developing Mauthner (M) neuron of vestibular axonal input to its lateral dendrite. After 8 days, 14 M cells were examined by light microscopy, and in each case the size and branching of the lateral dendrite was reduced. No consistent changes were observed in shape and size of other regions of the deprived cells or in the contralateral control cells. Synapses onto five of these pairs of cells were examined by electron microscopy. Except for missing vestibular terminals on the deprived dendrites, the synaptic input to the dendrites and to other regions of the M cell was normal in distribution and pattern. These data suggest that growth-promoting or trophic effects of vestibular axons upon the M cell are localized to its lateral dendrite.     

Isolation of putative glycoprotein gene from early somatic embryo of carrot and its possible involvement in somatic embryo development

Somatic embryogenesis is a unique process in plant cells. For example, embryogenic cells (EC) of carrot (Daucus carota) maintained in a medium containing 2,4-dichlorophenoxyacetic acid (2,4-D) regenerate whole plants via somatic embryogenesis after the depletion of 2,4-D. Although some genes such as C-ABI3 and C-LEC1 have been found to be involved in somatic embryogenesis, the critical molecular and cellular mechanisms for somatic embryogenesis are unknown. To characterize the early mechanism in the induction of somatic embryogenesis, we isolated genes expressed during the early stage of somatic embryogenesis after 2,4-D depletion. Subtractive hybridization screening and subsequent RNA gel blot analysis suggested a candidate gene, Carrot Early Somatic Embryogenesis 1 (C-ESE1). C-ESE1 encodes a protein that has agglutinin and S-locus-glycoprotein domains and its expression is highly specific to primordial cells of somatic embryo. Transgenic carrot cells with reduced expression of C-ESE1 had wide intercellular space and decreased polysaccharides on the cell surface and showed delayed development in somatic embryogenesis. The importance of cell-to-cell attachment in somatic embryogenesis is discussed.     

Verapamil inhibits proliferation but not steroidogenesis of regenerating rat adrenal cortex

The effect of verapamil, a calcium channel antagonist, on proliferation and steroidogenesis was investigated in regenerating rat adrenal cortex. Verapamil was given subcutaneously in two doses (1 and 5 mg/kg) to male Wistar rats subjected to adrenal enucleation combined with contralateral adrenalectomy. It was found that verapamil inhibited the mitotic activity of adrenocortical cells on the 4th and 8th day after surgery in a dose-dependent manner. However, no changes in corticosterone secretion were observed.     

Comparative histomorphology of the Mauthner cells in some freshwater teleosts.

The histomorphological observations are made on the Mauthner cells in eight species of teleosts belonging to six different families. The cells are better developed in Channa punctatus, Heteropneustes fossilis, Labeo rohita, Danio, malabaricus and Puntius ticto. They are symmetrically situated in Nandus nandus and are found to be absent in Mastocembalus armatus. Their position, shape and size vary in different species. The axon cap is well developed in Channa punctatus, Heteropneustes fossilis and carps. The cell body sends lateral and ventral dendrites besides several small dendrites. The lateral dendrite emerges through the axon cap, turns dorsolateral and becomes myelinated to form Mauthner axon. The Mauthner axon extends in the spinal region upto the caudal peduncle and forms synapses with the spinal motoneurons of the front column. There are numerous synapses and end bulbs from the vestibular fibres and VIIIth nerve distributed on the perikaryan of the Mauthner cell body. It is suggested that the Mauthner cells are comparatively well developed in those species in which the tail fin is better utilized for swimming.     

Effects of optokinetic stimulation on motor asymmetry in the goldfish

In goldfish fries, we examined the effect of the optomotor reaction (drive to swim toward moving images of vertical dark bars) on the behavioral motor asymmetry. Contralateral optokinetic stimulation of fishes (rotation of the bars against the direction preferred by fishes in their turnings) gradually smoothed and, later on, inverted the motor asymmetry, while the asymmetry underwent no modifications in the case of ipsilateral optokinetic stimulation (rotation of the bars in the direction similar to that preferred for turnings). Contralateral optokinetic stimulation also induced long-lasting inversion of the motor asymmetry of immobilized fishes deprived of the possibility to follow the movement of bar images. Ipsilateral optokinetic stimulation of fishes with the enucleation of the ipsilateral eye enhanced their motor asymmetry, while contralateral stimulation either did not modify the motor asymmetry of such individuals or inverted this feature. These data agree with the concept that, in fishes, one eye dominates and more actively provides tracking of the movement of bars, while another eye is a subdominant one. In general, we first found that the use of specific visual stimulation allows one to modify for a long time the behavioral motor asymmetry of the fishes, which, as is known, correlates with the morphofunctional asymmetry of Mauthner neurons (MNs). Visual information that activates MNs influences mostly the ventral dendrites of these neurons; thus, our findings allow us to believe that stimulations, which initiate the optomotor reaction, can serve as an adequate physiological model of natural visual stimulation of MNs (with projection of the respective influences on the ventral dendrites of the above cells). The use of such an experimental paradigm opens up new possibilities for studies of the role of these dendrites in the functions of MNs and of the plasticity of morphofunctional organization of these cells. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 133–145, March–April, 2007.     

A Connectionist Model of Left-Right Sound Discrimination by the Mauthner System

Artificial neural networks were used to explore the auditory function of the Mauthner system, the brainstem circuit in teleost fishes that initiates fast-start escape responses. The artificial neural networks were trained with backpropagation to assign connectivity and receptive fields in an architecture consistent with the known anatomy of the Mauthner system. Our first goal was to develop neurally specific hypotheses for how the Mauthner system discriminates right from left in the onset of a sound. Our model was consistent with the phase model for directional hearing underwater, the prevalent theory for sound source localization by fishes. Our second goal was to demonstrate how the neural mechanisms that permit sound localization according to the phase model can coexist with the mechanisms that permit the Mauthner system to discriminate between stimuli based on amplitude. Our results indicate possible computational roles for elements of the Mauthner system, which has provided us a theoretical context within which to consider past and future experiments on the cellular physiology. Thus, these findings demonstrate the potential significance of this approach in generating experimentally testable hypotheses for small systems of identified cells.     

Age-related differences in skeletal muscle protein synthesis: relation to markers of immune activation

A quantitative analysis of zone-specific proliferation was done to determine the recovery of adrenal cortical zonation during regeneration after enucleation. Adult male rats underwent adrenal enucleation [unilateral enucleation (ULE)] or sham surgery, both accompanied by contralateral adrenalectomy. At 2, 5, 10, and 28 days, blood and adrenals were collected to assess functional recovery. Adrenal sections were immunostained for Ki67 (proliferation), cytochrome P-450 aldosterone synthase (P-450aldo, glomerulosa), and cytochrome P-450 11beta-hydroxylase (P-45011beta, fasciculata). Unbiased stereology was used to count proliferating glomerulosa and fasciculata cells. Recovery of fasciculata secretory function occurred by 28 days as reflected by plasma ACTH and corticosterone, whereas glomerulosa function reflected by plasma aldosterone remained low at 28 days. At 5 days, ULE adrenals showed increased Ki67+ cells in the glomerulosa and inner fasciculata, whereas at 10 and 28 days increased proliferation was restricted to the outer fasciculata. These data show that enucleation results in transient elevations in glomerulosa and inner fasciculata cell proliferation followed by a delayed increase in the outer fasciculata. To assess adrenal growth in enucleated adrenals previously suppressed by the presence of an intact adrenal, rats underwent ULE and sham surgery; after 4 wk, the intact adrenal was removed and enucleated adrenals were collected at 2, 5, and 10 days. Overall, proliferation was delayed in this model, but at 5 days, Ki67+ cells increased in the outer fasciculata, whereas by 10 days, increased proliferation occurred in the outer and inner fasciculata. The key novel finding of increased proliferation in the inner fasciculata suggests that the delayed growth of the enucleated adrenal results in part from a regenerative response.     

Antioxidants and total oxyradical scavenging capacity during grass shrimp, Palaemonetes pugio, embryogenesis

During embryogenesis in grass shrimp the capacity to scavenge oxyradicals increased as measured by the Total Oxyradical Scavenging Capacity (TOSC) assay. The increase in TOSC during embryogenesis was associated with increasing concentrations of a number of antioxidants, including coenzyme Q (ubiquinone), alpha-tocopherol and reduced glutathione. Glutathione concentrations ranged from 0.004 to 0.005 nmol/embryo in early embryo stages and reached concentrations between 0.16 to 0.23 nmol/embryo in late embryo stages. Ascorbate remained essentially constant (0.16-0.20 nmol/embryo) throughout embryogenesis and may provide the preponderance of TOSC during early embryo development. Carotenoids were associated with yolk lipovitellin and these antioxidants decreased as yolk was absorbed during embryogenesis. Astaxanthin and beta-carotene were identified in embryos with astaxanthin always the principal carotenoid. In early embryo stages there are maternally derived antioxidants but as embryogenesis proceeds there is an assembly of a complex antioxidant system by newly formed cells and tissues.