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H T Cline

Publications and source records attributed to H T Cline.

14 recordsLinked to original sources
PubMed1991

Activity-dependent plasticity in the visual systems of frogs and fish.

The retinotectal system of lower vertebrates has provided considerable insight into the cellular mechanisms underlying the development and maintenance of orderly visual projections to the brain. This review will briefly summarize some of the data on the activity-dependent components of these mechanisms and incorporate the data into a model for selective synapse stabilization of coactive synapses. The model, based on the Hebbian synapse, is similar to models of long-term potentiation (LTP) of synaptic transmission, which are thought to account for the increased synaptic efficacy observed after associative conditioning paradigms. However, more recent data from two studies, one using confocal microscope analysis of migrating retinal arbors in vivo and the other investigating the requirement for protein kinase activity in map formation, point to a possible divergence in the cellular events underlying synapse stabilization in the developing visual system of the frog and LTP in the mammalian hippocampus.

Animals↗
PubMed1991

Glutamate-induced increases in intracellular Ca2+ in cultured frog tectal cells mediated by direct activation of NMDA receptor channels.

Influx of Ca2+ through NMDA channels may initiate the stabilization of coactive synapses during development of the retinotectal projection in frogs. Ca2+ imaging techniques were applied to cultured tectal cells to investigate whether excitatory amino acids cause a rise in [Ca2+]i. High [K+], NMDA, and glutamate increase [Ca2+]i in about 75% of the cells. NMDA and glutamate responses were completely blocked in the absence of extracellular Ca2+ and by the NMDA receptor or channel blockers APV and MK-801. The NMDA response was also blocked by Mg2+. Quisqualate and kainate produced little or no rise in [Ca2+]i. These studies indicate that when tectal cells are exposed to the retinal ganglion cell transmitter glutamate, the predominant means of Ca2+ entry is through NMDA channels.

2-Amino-5-phosphonovalerate↗
PubMed1991

Chronic application of NMDA decreases the NMDA sensitivity of the evoked tectal potential in the frog.

The activity-dependent mechanism that refines the topography of the retinotectal projection in frogs is mediated by the NMDA receptor. Earlier studies found that chronic treatment of the optic tectum with the NMDA receptor antagonist DL-2-amino-5-phosphonovaleric acid (DL-AP5) desegregated eye-specific stripes in three-eyed frogs, while chronic treatment with NMDA sharpened stripe borders (Cline et al., 1987; Cline and Constantine-Paton, 1990). We now report that this same chronic treatment with NMDA decreases the electro-physiologically measured sensitivity of the optic tectum to applied NMDA: acute application of a given concentration of NMDA decreased the evoked tectal potential to a lesser extent in animals chronically treated with NMDA than it did in normal and sham-treated animals. This is observed as a shift to the right in the NMDA dose-response curves for both the positive and negative postsynaptic components of the evoked tectal response. We believe that this decreased NMDA receptor effectiveness further restricts the intermingling of axon branches from the two eyes by limiting synapse stabilization to areas where afferent activity is most correlated. This would account for the anatomical sharpening of stripe borders (i.e., increased afferent segregation). Quantitative autoradiographic analysis of 3H-glutamate binding to NMDA receptors indicated that binding densities within the tectum did not differ between control groups and NMDA chronically treated groups. We suggest that in the experimental animals the response to NMDA may be decreased by a change in the effectiveness of individual NMDA receptors rather than by decreases in receptor number. This experimentally induced change may be analogous to naturally occurring decreases in receptor function that correlate with the end of some periods of visual plasticity in mammals.

2-Amino-5-phosphonovalerate↗
PubMed1990

Activity-dependent tuning and the NMDA receptor.

The refinement of the topographic map of visual space within the optic tectum of the frog is activity-dependent. The use of the three-eyed frog preparation to assay the operation of this fine-tuning mechanism indicates that this process is mediated by the NMDA receptor: Chronic in vivo treatment with APV, an NMDA antagonist, disrupts the segregation of retinal afferents into eye-specific zones while NMDA treatment sharpens this pattern. This latter effect is accompanied by a decreased sensitivity of the system to applied NMDA. Activation of the NMDA receptor may mediate the fine-tuning mechanism by initiating the stabilization of appropriate synapses. The requirements for NMDA receptor activation necessitate the convergence of terminals carrying correlated activity patterns. Such patterns of activity are provided by ganglion cells whose cell bodies lie near one another in the retina, and who should therefore, in an accurate visual map, terminate near one another in the tectum. Synapses from ganglion cells who do not neighbor one another in the retina have uncorrelated firing patterns and therefore do not activate the NMDA receptor. These synapses then would not be stabilized relative to one another. In addition to organizing the retinal projection, NMDA receptor activation may also modulate retinal ganglion cell arbor morphology, since chronic in vivo APV or NMDA treatments decrease arbor density. These results are discussed in terms of the effect of NMDA receptor activation on branch initiation and the rate of branch retraction.

Animals↗
PubMed1990

The role of the NMDA receptor in the development of the frog visual system.

The importance of patterned retinal activity in visual system development has been recognized since Hubel and Wiesels early experiments (1963). The NMDA receptor is one cellular mechanism which can recognize patterned retinal activity and convey an intracellular message of that activity. It will now be of considerable interest to elucidate the cellular events involved in synapse stabilization subsequent to NMDA receptor activation.

Animals↗
PubMed1990

The differential influence of protein kinase inhibitors on retinal arbor morphology and eye-specific stripes in the frog retinotectal system.

We investigated retinal axon morphology and eye-specific afferent termination zones in the optic tectum of three-eyed tadpoles that were chronically treated with protein kinase inhibitors. The kinase inhibitors sphingosine, H-7, and phorbol ester, which down-regulates protein kinase C with chronic exposure, were applied to the tecta in a slow release plastic, Elvax. In vivo protein phosphorylation assays in drug-treated tadpoles indicated that the treatments decreased 32P incorporation into some protein bands by as much as 60%. Although the drugs did not cause a desegregation of the eye-specific stripes, treated retinal axon arbors covered about half the area covered by untreated arbors or arbors treated with inactive analogs of the drugs. We conclude that eye-specific segregation can be maintained under conditions that markedly alter retinal ganglion cell axon arbor size and that significantly perturb protein phosphorylation. Furthermore, we conclude that the protein kinase(s) that we blocked with these treatments is involved in the growth of axon arbors.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1990

NMDA receptor agonist and antagonists alter retinal ganglion cell arbor structure in the developing frog retinotectal projection.

The development of sensory maps is thought to require an activity-dependent structural rearrangement of afferent terminal arbors within the CNS which recreates the topographic relations of sensory somata present in the periphery. In the frog retinotectal projection, activation of the NMDA receptor plays a role in this structural plasticity. Exposure of the optic tectum of tadpoles to NMDA receptor antagonists results in a rearrangement of retinal ganglion cell arbors so that their organization into a topographic projection and eye-specific stripes is disrupted (Cline et al., 1987; Cline and Constantine-Paton, 1989). Exposure of the optic tectum to the receptor agonist, NMDA, increases the eye-specific segregation of these arbors (Cline et al., 1987). We examined the projection of the supernumerary retina and the morphology of individual retinal afferent arbors of untreated, NMDA-treated, APV-treated, MK801-treated, and MK801/NMDA-treated 3-eyed tadpoles and young postmetamorphic frogs in an effort to understand how NMDA receptor activation is involved in the growth and ordering of retinal arbors. Treatments with MK801 in combination with NMDA resulted in a desegregation of eye-specific stripes, whereas treatments with MK801 or NMDA alone did not. As reported previously, APV treatment resulted in stripe desegregation without increasing the tangential area (measured from 2-dimensional drawings) of the terminal arbors. However, a detailed analysis revealed that the APV-treated tadpole arbors have 35% reduction in branch density (branch tips/area) compared to untreated 3-eyed tadpole arbors. We treated the optic tectum with a range of concentrations of NMDA prepared in the slow-release plastic Elvax. NMDA at 10(-4) M in Elvax was the optimal concentration to produce the sharpening of stripe borders. Exposure of the tectum to NMDA at 10(-6) M in Elvax produced no change in the stripe pattern, while 10(-2) M NMDA in Elvax resulted in beading of the arbors. At the optimal concentration NMDA treatment results in a 75% reduction in the number of axons crossing from a stripe to an interstripe zone. Drawings of individual HRP-labeled, NMDA-treated arbors demonstrate that they have fewer branch points and fewer branch tips. NMDA treatment reduced arbor density by approximately 50%. Arbors drawn from untreated postmetamorphic frogs have twice the branch density of arbors from untreated tadpoles. NMDA treatment in these animals reduced the branch density by 55%, comparable to the reduction seen in tadpole branch density. Our data support a specific hypothesis for NMDA receptor involvement in the activity-dependent structural refinement process within the developing retinotectal projection.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

Quantitative autoradiographic localization of NMDA, quisqualate and PCP receptors in the frog tectum.

An organizing role for the N-methyl-D-aspartate (NMDA) receptor/channel has been suggested in the development of the retinotectal projection in Rana pipiens. The regional distributions of NMDA, phencyclidine (PCP) and quisqualic acid (QA) receptors were quantified using in vitro autoradiography in the tectum of normal and surgically produced 3-eyed juvenile frogs. NMDA and QA receptor binding was highest in the pretectum. Of the tectal layers, the superficial retinotectal synaptic zone, layer 9, had the highest amount of NMDA and QA receptor binding. Moderate binding was observed in layer 5, with little binding in the cellular layer 6. No specific [3H]N-(1-[2-thienyl]cyclohexyl) piperidine ([3H]TCP) binding was observed in any of the tectal regions.

Animals↗
PubMed1989

NMDA receptor antagonists disrupt the retinotectal topographic map.

We tested the effect of two NMDA receptor antagonists, APV or MK801 (with NMDA), and the receptor agonist NMDA on the maintenance of retinal topography in frogs. Topography was assayed by measuring the dispersion of retrogradely labeled ganglion cells following a local HRP injection into the tectum. In untreated tadpoles, labeled cells covered about 5% of the retinal area. In APV- or MK801/NMDA-treated tadpoles, labeled ganglion cells covered 17% and 10% of the retinal area, respectively. Neither treatment with L-APV nor with NMDA disrupts the fidelity of the retinotectal projection. Neither APV- nor NMDA-treated ganglion cell terminals differed from untreated terminals with respect to tangential area, branch number, or branch density. These data support a role for the NDMA receptor in visual system development.

2-Amino-5-phosphonovalerate↗
PubMed1987

N-methyl-D-aspartate receptor antagonist desegregates eye-specific stripes.

The optic tecta of surgically produced three-eyed tadpoles were chronically exposed to the N-methyl-D-aspartate (NMDA) receptor antagonist aminophosphonovaleric acid (APV), or to NMDA itself, to assess the influence of NMDA receptor/channels on the eye-specific segregation of retinal ganglion cell (RGC) terminals that occurs whenever two retinas innervate one tectal lobe. Exposure of the tectum to the active isomer of APV produces desegregation of the RGC terminals without blocking electrical activity in the afferents or altering their terminal arbor morphology. Exposure to the inactive isomer of APV causes no perturbation of the normal stripe pattern. APV-induced desegregation is completely reversible within 2 weeks of removal of the APV. In addition, exposure of the optic tectum to NMDA results in stripes with sharper borders and fewer forks and fusions than untreated animals. These results suggest that the NMDA receptor/channel plays a role in eye-specific segregation in the three-eyed tadpole.

2-Amino-5-phosphonovalerate↗
PubMed1987

Development of neurotransmitter metabolism in embryos of the leech Haementeria ghilianii.

We have investigated the development of neurotransmitter metabolism in embryos of the glossiphoniid leech Haementeria ghilianii. The neurotransmitter content of dissected embryonic tissues was measured by means of radioenzymatic assays, while the presence of neurotransmitters in individual identified neurons was detected by means of immunocytochemical and monoamine histofluorescence techniques. The capacity for synthesis of neurotransmitters was measured by incubating dissected embryonic tissues in radiolabeled neurotransmitter precursors. A specific neurotransmitter uptake system present in some neurons was detected by means of an autoradiographic technique. At an early stage of development of the nervous system, when most neurons are just beginning process outgrowth, the nerve cord acquires the capacity to synthesize ACh, 5-HT, and GABA from their immediate precursors, and contains ACh. Moreover, 5-HT-immunoreactive neurons and neurons that are capable of GABA uptake can be identified. Dopamine-containing neurons are first detected by their histofluorescence at a slightly later stage, after process outgrowth is under way. As development continues, the content of and capacity for synthesis of these neurotransmitters increase, as does the number of neurons capable of GABA uptake. During the earlier stages of development, ACh content exceeds 5-HT content, which in turn exceeds dopamine content. By the end of embryogenesis, however, 5-HT and dopamine contents have greatly increased relative to ACh content, with 5-HT content exceeding ACh content by a factor of 2. Of the neurotransmitters thus far studied, 5-HT is present in the highest amount in the juvenile and adult nerve cord. Our results indicate that in the development of the leech nervous system neurotransmitter metabolism is one of the first neuronal characters to differentiate and that the subsequent levels of the different neurotransmitters are differentially regulated.

Acetylcholine↗
PubMed1986

Evidence for GABA as a neurotransmitter in the leech.

In the leech, Hirudo medicinalis, the inhibitory motor neurons to the longitudinal muscles in the body wall, cells 1 and 2, are linked via central inhibitory synapses to the excitatory motor neurons innervating the same muscles. Examination of these synapses showed that the inhibitors are GABAergic according to several electrophysiological and pharmacological criteria. Presynaptic release of neurotransmitter during passage of depolarizing current into the inhibitors, as well as direct application of GABA to the excitor cell bodies, hyperpolarizes the postsynaptic excitor. Moreover, both synaptic and extrasynaptic GABA receptors of the excitors are specifically blocked by the GABA antagonist bicuculline methiodide. The inhibitors, dissected from the ganglion and grown in culture, synthesize GABA when exposed to the GABA precursor glutamate, whereas the excitors do not synthesize detectable levels of GABA under these same conditions. The innervation and neurotransmitter sensitivity of the longitudinal muscles in the body wall of the glossiphoniid leeches Haementeria ghilianii and H. officinalis were examined in order to determine if the inhibitory neurotransmitter at the neuromuscular junction is GABA. Individual muscle fibers are innervated by both inhibitory and excitatory motor neurons in a manner such that the inhibitory and excitatory nerve terminals and neurotransmitter receptors are spatially and electrically separate. Intracellular recordings taken from the muscle fibers reveal a resting potential of about -70 mV. The amplitude of the spontaneous inhibitory junctional potentials (IJPs) falls to zero at a polarization of about -65 mV and reverses in sign at the normal resting potential.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗