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J J LoTurco

Publications and source records attributed to J J LoTurco.

At least 19 recordsLinked to original sources
PubMed2001

Impaired detection of variable duration embedded tones in ectopic NZB/BINJ mice.

Utilizing rodent models, prior research has demonstrated a significant association between focal neocortical malformations (i.e. induced microgyria, molecular layer ectopias), which are histologically similar to those observed in human dyslexic brains, and rate-specific auditory processing deficits as seen in language impaired populations. In the current study, we found that ectopic NZB/BINJ mice exhibit significant impairments in detecting a variable duration 5.6 kHz tone embedded in a 10.5 kHz continuous background, using both acoustic reflex modification and auditory event-related potentials (AERP). The current results add further support to the association between focal cortical malformations and impaired auditory processing, and the notion that these auditory effects may occur regardless of the cortical location of the anomaly.

Acoustic Stimulation↗
PubMed2001

Altered interneuron development in the cerebral cortex of the flathead mutant.

One approach to defining mechanisms essential to neocortical development is to analyze the phenotype of novel spontaneous mutations that dramatically affect the generation and differentiation of different neocortical neurons. Previously we have shown that there is a large decrease in the total number of cortical neurons in the flathead mutant rat, and in this paper we show that the flathead (fh/fh) mutation causes an even larger decrease in the number of interneurons. The decrease in relative interneuron number is different in different cortical lamina and for different interneuron subtypes. Specifically, the percentage of GABA and calretinin- positive cells in upper layers of somatosensory cortex is not appreciably decreased in homozygous mutants, while other interneuron subtypes in somatosensory cortex and all GABA-positive interneuron types in entorhinal cortex are decreased. In addition, the soma and dendritic arbors of interneurons in flathead are greatly hypertrophied, while those of pyramidal neurons are not. Furthermore, we found that at embryonic day 14, flathead mutants display high levels of cell death throughout both the neocortical and ganglionic eminence (GE) proliferative zones with a larger increase in cell death in the GE than in the neocortical VZ. In addition, we provide evidence that there is widespread cytokinesis failure resulting in binucleate pyramidal cells and interneurons, and the number of binucleate interneurons is greater than the number of binucleate pyramidal neurons. Together, these results demonstrate that the fh mutation causes dramatic alterations in interneuron development, and suggest that the flathead mutation causes differential cytokinesis failure and cell death in different types of neocortical progenitors.

Animals↗
PubMed2001

Electrophysiological and morphological characterization of neurons within neocortical ectopias.

Focal developmental abnormalities in neocortex, including ectopic collections of neurons in layer I (ectopias), have been associated with behavioral and neurological deficits. In this study, we used infrared differential interference contrast microscopy and whole cell patch-clamp to complete the first characterization of neurons within and surrounding neocortical ectopias. Current-clamp recordings revealed that neurons within ectopias display multiple types of action potential firing patterns, and biocytin labeling indicated that approximately 20% of the cells in neocortical ectopias can be classified as nonpyramidal cells and the rest as atypically oriented pyramidal cells. All cells had spontaneous excitatory (glutamatergic) and inhibitory (GABAergic) postsynaptic currents. Exhibitory postsynaptic currents consisted of both N-methyl-D-aspartate (NMDA) receptor-mediated and AMPA/kainate (A/K) receptor-mediated currents. The NMDA receptor-mediated component had decay time constants of 15.35 +/- 2.2 (SE) ms, while the A/K component had faster decay kinetics of 7.6 +/- 1.7 ms at -20 mV. GABA(A) receptor-mediated synaptic currents in ectopic cells reversed at potentials near the Cl- equilibrium potential and had decay kinetics of 16.65 +/- 1.3 ms at 0 mV. Furthermore we show that cells within ectopias receive direct excitatory and inhibitory input from adjacent normatopic cortex and can display a form of epileptiform activity.

Afferent Pathways↗
PubMed2000

In vitro biocytin injection into perinatal mouse brain: a method for tract tracing in developing tissue.

Injection of biocytin provides an effective method for labeling axonal projections. Several difficulties arise when this technique is employed in fetal or early postnatal animals in vivo, including limited access to injection sites and extended post-injection survival periods. To circumvent these problems, we adapted the technique of extracellular biocytin injection for use in explanted brain hemispheres of developing mice. Briefly, entire brain hemispheres from perinatal mice (E16-P9) were removed and placed in oxygenated aCSF in a brain slice recording chamber. Following visually guided injection of biocytin (2%) into the prelimbic cortex, the brains were then incubated in oxygenated artificial cerebrospinal fluid (aCSF) for varying periods of time and then immersion-fixed in 4% paraformaldehyde and 0.5% glutaraldehyde. The next day, the brains were sectioned and processed for biocytin histochemistry using the avidin-biotin-complex method. We examined the method of injection, electrode type, time of injection, and post-injection incubation period. We found that in E16-P9 animals iontophoresis of biocytin using 8- to 12-megaohm patch clamp electrodes for a duration of 10 min provides optimal axonal labeling. Post-injection incubation times of four or more hours are sufficient for labeling fine caliber collaterals as well as axon bundles that reach distances over 3 mm. In vitro injection of biocytin into explanted brain hemispheres provides a quick and easy method for tract tracing in developing brains.

Animals↗
PubMed2000

The flathead mutation causes CNS-specific developmental abnormalities and apoptosis.

We describe a new mutation, flathead (fh), that arose spontaneously in an inbred colony of Wistar rats. The mutation is autosomal recessive, and the behavioral phenotype of fh/fh rats includes spontaneous seizures, tremor, impaired coordination, and premature death. A striking feature of the fh mutation is a dramatic reduction in brain size (40% of normal at birth). In contrast, no abnormalities are evident in the peripheral nervous system or in other tissues outside of the CNS. Although bromodeoxyuridine incorporation assays indicate that the rate of cell proliferation in the fh/fh cortex is similar to that of unaffected animals, in situ terminal deoxynucleotidyl transferase-mediated dUTP-biotin end-labeling assays reveal a dramatic increase in apoptotic cell death beginning after embryonic day 16 (E16). At E18 there is a 20-fold increase in cell death in the ventricular zone of fh/fh neocortex, and at postnatal day 1 (P1), the number of apoptotic cells is still two times that of normal. However, by P8 the extent of cell death in fh/fh is comparable to that of unaffected littermates, indicating that the reduction in brain growth is caused by abnormally high apoptosis during a discrete developmental period. Late-developing structures such as the cerebellum, neocortex, hippocampus, and retina are most severely affected by the fh mutation. Within these structures, later-generated neuronal populations are selectively depleted. Together, these results suggest that the flathead gene is essential for a developmental event required for the generation and maturation of late-born cell populations in the brain.

Animals↗
PubMed2000

Neocortical ectopias are associated with attenuated neurophysiological responses to rapidly changing auditory stimuli.

Developmental dyslexia has been separately associated with the presence of ectopic collections of neurons in layer I of neocortex (ectopias) and with alterations in processing rapidly changing stimuli. We have used BXSB/MpJ-Yaa mice, some of which have neocortical ectopias, to directly test the hypothesis that ectopias may alter auditory processing. Auditory event related potentials (AERPs) were elicited by pairs of 10.5 kHz tones separated by silence, 0.99 kHz, or 5.6 kHz tones of variable duration. Half of the mice tested had 1-3 ectopias in frontal or parietal cortex, and half had no ectopias. Mice with ectopias showed a reduced response to the second 10.5 kHz stimuli only when it was preceded by short duration 5.6 kHz tones. These results indicate that BXSB mice are an excellent model for determining how focal neocortical anomalies alter sensory processing.

Acoustic Stimulation↗
PubMed2000

Noggin is a negative regulator of neuronal differentiation in developing neocortex.

Bone morphogenetic proteins (BMPs) trigger neuronal differentiation of neocortical precursors within the ventricular zone (VZ) [Li et al. (1998): J Neurosci 18:8853-8862]. BMP-2/4 protein is concentrated at the VZ surface and BMPs rapidly promote the differentiation of neocortical precursors in both dissociated cell and explant cultures. Noggin binds to BMP-2/4 with high affinity, and prevents binding to cell surface receptors. In the present study, we used human recombinant noggin protein to determine whether endogenous BMP-2/4 triggers neuronal differentiation in dissociated cell culture. We find that noggin inhibits the differentiation of neocortical neurons: noggin decreases the number of MAP-2- and TUJ1-positive cells after 24 h of treatment, yet has no effect on either proliferation or cell survival. Noggin also significantly decreases neurite growth of MAP-2-positive cells. In addition, using Western blot analysis we show that noggin protein is present in developing cortex at E15. These results are consistent with previous results showing that endogenous BMPs trigger neuronal differentiation in the neocortical VZ and also indicate that a balance of noggin and BMP may regulate the differentiation of neocortical neurons in vivo.

Animals↗
PubMed1999

Differential regulation of connexin 26 and 43 in murine neocortical precursors.

Proliferating cells of the developing murine neocortex couple together into clusters during neurogenesis. Previously, we have shown that these clusters contain neural precursors in all phases of the cell cycle except M phase, and that they extend a nestin-expressing process from the cluster to the pial surface. In addition, coupling within neocortical cell clusters is a dynamic process related to the cell cycle, with maximal coupling in S/G2 phase, uncoupling in M phase and then recoupling during G1 and S phases of the cell cycle. In the present study, we use immunohistochemistry to demonstrate that cycling neocortical cells as well as radial glial cells express the gap junction proteins connexin 26 and connexin 43. Furthermore, we demonstrate that biocytin labeled clusters extend processes to the pial surface that express the glial cell antigen RC2. Lastly, by combining bromodeoxyuridine and connexin immunohistochemistry on acutely dissociated neocortical cells, we show that the percentage of cycling cells immunoreactive to connexin 26 and connexin 43 changes through the cell cycle. These results indicate that radial glial cells as well as neural precursors couple into clusters, and suggest that through differential regulation of connexins, neocortical precursors may compartmentalize as they progress through the cell cycle.

Animals↗
PubMed1999

Characterization of seizures in the flathead rat: a new genetic model of epilepsy in early postnatal development.

PURPOSE: Disorders in normal central nervous system (CNS) development are often associated with epilepsy. This report characterizes seizures in a novel genetic model of developmental epilepsy, the Flathead (FH) rat. METHODS: Animals (n = 76) ages P0-22 were monitored for clinical and electrographic seizure activity. The effects of various AEDs on seizure frequency and duration also were assessed: phenobarbital (PB; 40 mg/kg), valproate (VPA; 400 mg/kg), or ethosuximide (ESM; 600 mg/kg). RESULTS: FHs display episodes of behavior characterized by whole-body tremor, strub tail, alternating forelimb clonus, and complete tonus. EEG recordings from neocortex reveal that FH seizures are bilateral and begin around P7. Seizures occur at a frequency of approximately six per hour from P7 to P18 and the average duration of seizures increases through development. PB, VPA, and ESM failed to prevent seizures; however, PB significantly increased the interval of seizures but had no effects on the duration of seizures, whereas VPA decreased the duration of seizures and not the interval. CONCLUSIONS: Seizures in FH rats occur at a constant and high frequency through a defined period in early postnatal development, and these seizures are not completely blocked by high doses of PB, VPA, or ESM. Because FH is a single-locus mutant displaying a highly regular pattern of seizure activity, it is an ideal model for examining the process of epileptogenesis in the developing brain, evaluating new AED therapies, and determining the identity of a gene essential to the normal development of cortical excitability.

Animals↗
PubMed1998

Neuronal differentiation of precursors in the neocortical ventricular zone is triggered by BMP.

Neocortical neurons begin to differentiate soon after they are generated by mitoses at the surface of the ventricular zone (VZ). We provide evidence here that bone morphogenetic protein (BMP) triggers neuronal differentiation of neocortical precursors within the VZ. In cultures of dissociated neocortical neuroepithelial cells, BMPs increase the number of MAP-2- and TUJ1-positive cells within 24 hr of treatment. In explant cultures, BMP-4 treatment leads to an increase in the number of TUJ1-positive cells within the ventricular zone. Furthermore, truncated, dominant-negative, BMP type I receptor, introduced into neocortical precursors by retrovirus-mediated gene transfer, blocks neurite elaboration and migration out of the VZ. Finally, immunocytochemistry indicates that BMP protein is present at the VZ surface. Together, these results indicate that BMP protein is present within the VZ, that BMP is capable of promoting neuronal differentiation, and that signaling through BMP receptors triggers neuronal precursors to differentiate and migrate out of the VZ.

Animals↗
PubMed1998

A gene essential to brain growth and development maps to the distal arm of rat chromosome 12.

A recently discovered, spontaneous, autosomal recessive mutation in rats, flathead (fh), results in greatly reduced brain growth beginning in late fetal development. In this study we have mapped the fh mutation by determining the pattern of segregation of polymorphic microsatellite markers with respect to fh in 51 affected F2 offspring from a single interstrain intercross. Two markers on chromosome 12, D12Rat80 and D12Mgh6, cosegregated with the fh mutation in all 51 affected animals. The distribution of six additional markers in 40 informative meioses further localizes fh approximately 2 cM teleomeric to nos1. There are no known mutations in homologous regions of either mouse or human genomes that result in deficits in late neurodevelopment similar to that observed in fh/fh animals. The unique phenotype of fh/fh animals and the location of fh suggests the presence of a novel gene essential to normal brain development on the distal end of rat chromosome 12.

Aging↗
PubMed1998

Early patterning of prelimbic cortical axons to the striatal patch compartment in the neonatal mouse.

The striatum receives excitatory input from virtually the entire cerebral cortex. In the adult, this input is segregated into two functionally distinct compartments of the striatum, the patch (striosome) and matrix regions. This study determined whether the patterning of corticostriatal afferents from the prelimbic cortex to the striatal patch compartment develops during the early period of collateral formation or instead at the time of peak synaptogenesis. Initial formation of corticostriatal axon collaterals was observed by embryonic day (E) 19. Quantification of corticostriatal collaterals revealed a significant increase in the number and complexity of collateral branches at postnatal day 6 as compared to E19. Concomitant with the increase in collateral branching, a heterogeneous pattern of collateralization consisting of parallel rows of corticostriatal collaterals was observed in the medial striatum. In addition to the rows, clusters of corticostriatal axons occurred more laterally. These clusters colocalized with patches of dense tyrosine hydroxylase-positive fibers, a marker for the striatal patch compartment in the neonatal mouse. Together, these data indicate that corticostriatal patterning occurs during the period of early axon collateralization resulting in a segregation of corticostriatal axon collaterals from the prelimbic cortex to the striatal patch compartment.

Animals↗
PubMed1997

Cell coupling and uncoupling in the ventricular zone of developing neocortex.

Cells within the ventricular zone (VZ) of developing neocortex are coupled together into clusters by gap junction channels. The specific role of clustering in cortical neurogenesis is unknown; however, clustering provides a means for spatially restricted local interactions between subsets of precursors and other cells within the VZ. In the present study, we have used a combination of 5-bromo-2'-deoxyuridine (BrDU) pulse labeling, intracellular biocytin labeling, and immunocytochemistry to determine when in the cell cycle VZ cells couple and uncouple from clusters and to determine what cell types within the VZ are coupled to clusters. Our results indicate that clusters contain radial glia and neural precursors but do not contain differentiating or migrating neurons. In early neurogenesis, all precursors in S and G2 phases of the cell cycle are coupled, and approximately half of the cells in G1 are coupled. In late neurogenesis, however, over half of the cells in both G1 and S phases are not coupled to VZ clusters, whereas all cells in G2 are coupled to clusters. Increased uncoupling in S phase during late neurogenesis may contribute to the greater percentage of VZ cells exiting the cell cycle at this time. Consistent with this hypothesis, we found that pharmacologically uncoupling VZ cells with octanol decreases the percentage of VZ cells that enter S phase. These results demonstrate that cell clustering in the VZ is restricted to neural precursors and radial glia, is dynamic through the cell cycle, and may play a role in regulating neurogenesis.

Animals↗
PubMed1995

GABA and glutamate depolarize cortical progenitor cells and inhibit DNA synthesis.

We have found that, during the early stages of cortical neurogenesis, both GABA and glutamate depolarize cells in the ventricular zone of rat embryonic neocortex. In the ventricular zone, glutamate acts on AMPA/kainate receptors, while GABA acts on GABAA receptors. GABA induces an inward current at resting membrane potentials, presumably owing to a high intracellular Cl- concentration maintained by furosemide-sensitive Cl- transport. GABA and glutamate also produce increases in intracellular Ca2+ in ventricular zone cells, in part through activation of voltage-gated Ca2+ channels. Furthermore, GABA and glutamate decrease the number of embryonic cortical cells synthesizing DNA. Depolarization with K+ similarly decreases DNA synthesis, suggesting that the neurotransmitters act via membrane depolarization. Applied alone, GABAA and AMPA/kainate receptor antagonists increase DNA synthesis, indicating that endogenously released amino acids influence neocortical progenitors in the cell cycle. These results demonstrate a novel role for amino acid neurotransmitters in regulating neocortical neurogenesis.

Animals↗
PubMed1991

Initial expression and endogenous activation of NMDA channels in early neocortical development.

We have made patch-clamp recordings from slices of fetal and postnatal rat neocortex in order to study the initial expression and activation of NMDA channels. Recordings from both whole cells and outside-out patches indicated that functional NMDA channels are expressed on neurons within the cortical plate, but not on younger cells within the ventricular zone. The NMDA channels on cortical plate neurons had a unitary conductance of approximately 40 pS, had a mean open time of approximately 6 msec, required glycine to open, and were blocked in a voltage-dependent manner by magnesium. These precocious channels were present before the appearance of functional synaptic activity, yet like NMDA channels in the mature neocortex, they were spontaneously activated by an agonist within brain slices. These results demonstrate that NMDA channels are initially expressed on neocortical neurons some time between the last mitotic division within the ventricular zone and completion of migration into the cortical plate. These early NMDA channels have properties characteristic of NMDA channels on more mature neurons and are similarly activated by an endogenous agonist in situ. Their early appearance and activation indicate that NMDA channels may play a role during early stages of cortical development.

Aging↗
PubMed1990

Differential activation of glutamate receptors by spontaneously released transmitter in slices of neocortex.

Whole-cell recordings were made from neurons in neocortical brain slices in order to characterize excitatory synaptic currents mediated by glutamate receptors. Glutamate receptor antagonists, D-aminophosphonovalerate (D-APV) and CNQX, selectively attenuated distinct components in evoked synaptic currents, and were used to differentiate spontaneous synaptic currents mediated by N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Spontaneous excitatory synaptic currents were independent of action potentials, varied linearly with voltage, and were blocked by the non-NMDA receptor antagonist CNQX. An NMDA receptor-mediated component was not apparent in these spontaneous synaptic currents, however, when magnesium was omitted from the recording medium, fluctuations in current and sustained inward current became apparent, and these were blocked by the NMDA receptor antagonist D-APV. Based on these findings, we conclude that NMDA and non-NMDA receptors are activated differentially by transmitter released independently of action potentials.

Animals↗
PubMed1988

Reflex facilitation of the nictitating membrane response remains after cerebellar lesions.

Reflex facilitation and associated properties were investigated during classical conditioning of the nictitating membrane (NM) response in rabbit. In the first experiment, the role of the cerebellum was examined by comparing the unconditioned responses of animals with bilateral lesions of the deep cerebellar nuclei with those of operated controls during counterbalanced tone/light (T/L) discrimination training. Both T and L facilitated unconditioned NM responses when used as the CS+ (conditioned stimulus), but neither facilitated when used as the CS-. There were no significant differences in the amount of reflex facilitation exhibited by animals with lesions compared with control animals. Animals with lesions, however, failed to acquire conditioned responses after 10 days of training, whereas all control animals met acquisition criterion within 4 days. In the second experiment, reflex facilitation was shown to decrement in a stimulus-specific manner when nonreinforced presentations of an auditory stimulus were given. The discussion of results focuses on the relation between reflex facilitation and classical conditioning in terms of behavioral properties and underlying neural systems.

Acoustic Stimulation↗