Biomedical subjects

L Kojic

Publications and source records attributed to L Kojic.

9 recordsLinked to original sources

PubMed2001

Laminar distribution of cholinergic- and serotonergic-dependent plasticity within kitten visual cortex.

Both cholinergic and serotonergic modulatory projections to mammalian striate cortex have been demonstrated to be involved in the regulation of postnatal plasticity, and a striking alteration in the number and intracortical distribution of cholinergic and serotonergic receptors takes place during the critical period for cortical plasticity. As well, agonists of cholinergic and serotonergic receptors have been demonstrated to facilitate induction of long-term synaptic plasticity in visual cortical slices supporting their involvement in the control of activity-dependent plasticity. We recorded field potentials from layers 4 and 2/3 in visual cortex slices of 60--80 day old kittens after white matter stimulation, before and after a period of high frequency stimulation (HFS), in the absence or presence of either cholinergic or serotonergic agonists. At these ages, the HFS protocol alone almost never induced long-term changes of synaptic plasticity in either layers 2/3 or 4. In layer 2/3, agonist stimulation of m1 receptors facilitated induction of long-term potentiation (LTP) with HFS stimulation, while the activation of serotonergic receptors had only a modest effect. By contrast, a strong serotonin-dependent LTP facilitation and insignificant muscarinic effects were observed after HFS within layer 4. The results show that receptor-dependent laminar stratification of synaptic modifiability occurs in the cortex at these ages. This plasticity may underly a control system gating the experience-dependent changes of synaptic organization within developing visual cortex.

Animals↗

PubMed2001

Identification of a novel truncated isoform of trkB in the kitten primary visual cortex.

Neurotrophins have been shown to play important roles in development and plasticity of the visual cortex (VC). Since signal transduction of neurotrophins is mediated through neurotrophin receptors, we attempted to analyze neurotrophin receptors in the VC. In this study, we isolated cDNAs encoding the intracellular regions of truncated isoforms of the trkB receptor from 30-d-old kitten primary VC. Two distinct truncated isoforms of trkB were isolated and characterized by sequence analyses. One of the isoforms corresponds to the previously described truncated trkB in several mammalian species. The second isoform represents a novel truncated trkB variant form in the kitten VC. Sequence analysis revealed that this contains a sequence that has not yet been reported in any species. This novel isoform, designated trkB.T4, results from alternative splicing 189-bp (63 amino acids) downstream from the splice site giving rise to the first known truncated isoforms of trkB. In the context of recent hypotheses regarding the function of truncated trkB receptors, sequence analysis indicates that trkB.T4 may bear putative signaling/internalization sequences.

Amino Acid Sequence↗

PubMed2000

Columnar distribution of serotonin-dependent plasticity within kitten striate cortex.

Recent studies have identified the potential for an important role for serotonin (5-HT) receptors in the developmental plasticity of the kitten visual cortex. 5-HT(2C) receptors are transiently expressed in a patchy fashion in the visual cortex of kittens between 30-80 days of age complementary to patches demarcated by cytochrome oxidase staining. 5-HT, operating via 5-HT(2C) receptors, increases cortical synaptic plasticity as assessed both in brain slices and in vivo. Herein, we report that bath application of 5-HT substantially increases the probability of long-term potentiation within 5-HT(2C) receptor-rich zones of cortex, but this effect is not observed in the 5-HT(2C) receptor-poor zones. Instead, in these zones, 5-HT application increases the probability of long-term depression. These location-specific effects of 5-HT may promote the formation of compartment-specific cortical responses.

Acetylcholinesterase↗

PubMed2000

Confocal imaging of N-methyl-D-aspartate receptors in living cortical neurons.

The fluorescence-conjugated N-methyl-D-aspartate receptor-selective antagonist, BODIPY-conantokin-G, was employed to label N-methyl-D-aspartate receptors in living neurons derived from the visual cortex of embryonic rats. The fluorescent labeling was visualized and analysed using confocal microscopy and digital imaging techniques. BODIPY-conantokin-G binding sites were homogeneously distributed across somata four days after neurons (E17-20) were placed in culture. In five-day-old cultures, BODIPY-conantokin-G binding sites became clusters of fluorescently labeled spots which were arranged irregularly on somata and proximal neurites. Distal neurites displayed fluorescent labeling after 10-15 days in culture. Displacement experiments showed that spermine and unlabeled conantokin-G compete with BODIPY-conantokin-G labeling at the N-methyl-D-aspartate receptor-associated polyamine site. The N-methyl-D-aspartate receptor antagonist 2-amino-5-phosphonovaleric acid also depressed the labeling but with a weaker effect, probably due to interactions occurring between the N-methyl-D-aspartate receptor agonist binding site and the polyamine modulatory site. The fluorescent dyes FM 1-43 and FM 4-64 were used in double-labeling studies to compare the distribution of nerve terminals with that of BODIPY-conantokin-G binding sites. BODIPY-conantokin-G binding clusters were associated with presynaptic nerve terminals while isolated BODIPY-conantokin-G binding sites were not always opposed to terminals. The aggregation of receptors to form clusters may lead to the functional formation of excitatory synapses. To investigate whether modulation of membrane potentials affected the formation of N-methyl-D-aspartate receptor clusters, cultured neurons were chronically treated for a week with either tetrodotoxin (to block membrane action potentials) or a high concentration of potassium to depolarize the membrane. While neurons in the tetrodotoxin-treated group showed a similar number of fluorescently labeled clusters compared with the control group, neurons in the high potassium group exhibited a higher number of fluorescently labeled receptor clusters. These results suggest that more active neurons may tend to form more N-methyl-D-aspartate synapses during early development.

Age Factors↗

PubMed1997

Serotonin facilitates synaptic plasticity in kitten visual cortex: an in vitro study.

We have addressed the role of serotonin-2C (5-HT2C) receptors in the development and maintenance of synaptic plasticity in the kitten visual cortex. In visual cortical slices, taken from 40- to 80-day-old kittens, bath application of serotonin markedly facilitated the induction of both long-term depression (LTD) and long-term potentiation (LTP). Field potential responses to white matter stimulation were recorded from layer IV after a regime of low frequency stimulation (LFS; 1 Hz, 15 min), which reliably induced LTP or LTD in younger kittens (less than 30 days of age). At 40-80 days, this protocol almost never induced LTD or LTP in layer IV. However, in 50% of the visual cortical slices studied in 40-80-day-old kittens, LTD or LTP was induced, if serotonin (1 or 10 microM) was co-applied with LFS. No such serotonin facilitation of long-term plasticity was ever detected in > 120-day-old animals, indicating that serotonin facilitates synaptic plasticity within a defined period of visual cortical development. Serotonergic 5-HT2C receptors are likely to contribute to the synaptic plasticity observed in layer IV, since mesulergine, an antagonist of the 5-HT2C receptor, completely blocked synaptic modifications induced by the combination of low frequency stimulation and serotonin application.

Aging↗

PubMed1995

kappa-opioid receptor agonists modulate excitatory transmission in substantia gelatinosa neurons of the rat spinal cord.

This study examined the effects of selective activation of kappa 1-opioid receptors on excitatory transmission in substantia gelatinosa (SG) using intracellular recordings from SG neurons in transverse slices of the young rat lumbar spinal cord. Monosynaptic and polysynaptic excitatory postsynaptic potentials (EPSPs) were evoked by orthodromic electrical stimulation of A delta or C primary afferent fibers in the dorsal root after blocking inhibitory inputs with bicuculline and strychnine, NMDA receptors with D-2-amino-5-phosphonovaleric acid and mu- and delta-opioid receptors with CTAP and ICI 174,864, respectively. Bath application of dynorphin A1-17 or U-69, 593 caused dual modulation of the peak amplitude of presumed monosynaptic AMPA receptor-mediated EPSPs, decreasing synaptic potentials at nanomolar concentrations in a majority of SG cells examined (dynorphin, 63%; U-69,593, 91%), and increasing EPSPs at micromolar concentrations. Only the inhibitory action of dynorphin A1-17 was consistently and completely blocked by norbinaltorphimine (nor-BNI). Since U-69,593 and nor-BNI are selective for the kappa 1-opioid receptors, the depression of EPSPs is likely to be mediated by the kappa1-opioid receptors. Under conditions of blockade of synaptic transmission with TTX and mu-and delta-opioid receptors, dynorphin A1-17 and U-69,593 hyperpolarize most of SG neurons and decrease their membrane input resistance, the finding suggesting that direct interaction of kappa-agonists with a postsynaptic receptor is likely explanation for the inhibition of EPSPs. However, in some SG cells, the inhibition of EPSPs appears to be of presynaptic origin since dynorphin A1-17 and U-69,593 did depress the EPSPs in the absence of changes in passive membrane properties. Rp-cAMPS, a membrane permeant potent competitive inhibitor of cAMP-activated protein kinase, prevented the depressant effect of dynorphin A 1-17. This finding suggested a possibility that dynorphin A1-17, acting through a decrease in intracellular cyclic AMP levels, can reduce the synaptic responses of SG neurons. These results provide the first electrophysiological demonstration that the activation of kappa 1-opioid receptors inhibits AMPA receptor-mediated primary afferent neurotransmission in the substantia gelatinosa of the young rat spinal cord. This effect may mediate the ability of kappa-receptor agonists to produce antinociception.

Animals↗

PubMed1993

The selective activation of dorsal horn neurons by potassium stimulation of high threshold primary afferent neurons in vitro.

Intracellular recordings from neurons in the dorsal root ganglion and dorsal horn, in an in vitro spinal cord-dorsal root ganglion preparation, were used to investigate the role of large and small afferent fibers in the sensory synaptic transmission of the superficial dorsal horn. Raising the extracellular potassium concentration from 3.1 to 25-50 mM in the dorsal root ganglion compartment evoked a large amplitude depolarization and blocked action potentials in the large neurons of dorsal root ganglion, and it synaptically excited dorsal horn neurons. Excitatory postsynaptic potentials that were evoked by electrical stimulation of large myelinated fibers, but not those evoked by activation of small unmyelinated fibers, were blocked by the potassium treatment of the dorsal root. Tetrodotoxin (0.3-10 microM), when applied to the sensory neurons, abolished action potentials in large myelinated fibers but had no effect on the potassium-induced depolarization of the soma of large neurons of the dorsal root ganglion. Bath application of tetrodotoxin to the dorsal root ganglion blocked the postsynaptic potentials evoked in dorsal horn neurons by electrical stimulation of large fibers (stimulus intensity 10-20V, 0.02 ms) but failed to block postsynaptic potentials induced by electrical stimulation of slow fibers (stimulus intensity > 35 V, 0.5 ms). In addition, the tetrodotoxin failed to block the synaptic activation of dorsal horn neurons which was induced by the application of high potassium to sensory neurons. Capsaicin (10-100 microM, 10 s), applied to the sensory neurons, resulted in a prolonged synaptic activation of the dorsal horn neurons and a subsequent long lasting desensitization. During the period of capsaicin desensitization, synaptic activation of dorsal horn neurons by application of high potassium to the dorsal root ganglion and electrical stimulation of slow fibers was blocked. The opioid receptor agonist (D-Ala2, D-Leu5)-enkephalinamide (1 microM), applied to the spinal cord slice, abolished the dorsal horn neuron excitation evoked by electrical or chemical activation of slow primary afferent fibers. These findings indicate that high concentrations of K+ applied to the dorsal root ganglia selectively activate a primary afferent input to the dorsal horn, which is capsaicin sensitive and tetrodotoxin resistant.

Action Potentials↗

PubMed1989

Electro-acupuncture modifies humoral immune response in the rat.

The immunomodulating properties of "Shangqiu" (LP-5), "Ququan" (H-8), and "Rangu" (R-2) points were studied in several experiments performed on male Wister rats treated bilaterally by acupuncture (A) or electro-acupuncture (EA). On the stimulation day 3, the sheep-red-blood cells (SRBC) antigen was injected intraperitoneally and four days later, the immunological tests (plaque forming cells-PFC, direct microhemagglutination) were performed. Also, the relative weights of lymphoid organs (spleen and thymus) and adrenal gland were derived after sacrifice. The results obtained suggest pronounced immunomodulating properties of 200 Hz cathodal current stimulation at H-8 point. The immunosuppression observed reflected in a decreased number of PFC and reduced relative weights of adrenal gland revealed in all A- or EA-treated groups.

Acupuncture Analgesia↗

PubMedDate not supplied

Molecular analysis of trkC in the cat visual cortex.

trkC belongs to the trk family of neurotrophin receptors. Several isoforms of trkC have been cloned to date; a full-length catalytic form containing a tyrosine kinase (TK) domain, three full-length isoforms with amino-acid insertions (14, 25, and 39 amino acids) in the TK domain, and five noncatalytic truncated forms that completely lack the TK domain. These isoforms have been studied in several mammalian species, including the pig, rat, mouse, monkey, and human. In this article we report the cloning and sequencing of five trkC isoforms isolated from 30-d postnatal cat visual cortex. The first isoform corresponded to the previously reported full-length trkC transcript containing the 14 amino-acid insert. To search for the presence of other inserts, reverse transcription polymerase chain reaction (RT-PCR) was performed on 30-d postnatal cat visual cortex mRNA using primers that flank the insertion site in the TK domain. Both the isoform containing the 14 amino-acid insert and the isoform lacking any insertion were present in abundant amounts, whereas the other two insert containing isoforms (TK25 and TK39) were much less abundant. The fifth isoform discovered corresponds to the previously reported truncated transcript. Overall, there is a high degree of identity (89-98%) and homology (97-99%) between the cat trkC nucleotide and amino-acid sequences among all mammals. The extracellular juxtamembrane domain was found to be highly divergent among all mammals that have been studied to date. This divergent region also included a proline deletion in the cat trkC sequence. This is the first report of the cloning, sequencing, and RT-PCR analysis of trkC in cat visual cortex, a system extensively studied using anatomical and physiological approaches.

Amino Acid Sequence↗