Lesions of mediodorsal thalamic nucleus reverse abnormal firing of the medial prefrontal cortex neurons in parkinsonian rats.

The dysfunction of the medial prefrontal cortex is associated with affective disorders and non-motor features in Parkinson's disease. However, the exact role of the mediodorsal thalamic nucleus in the function of the prefrontal cortex remains unclear. To study the possible effects of the mediodorsal thalamic nucleus on the neurological function of the medial prefrontal cortex, a model of Parkinson's disease was established by injecting 8 µg 6-hydroxydopamine into the substantia nigra compacta of rats. After 1 or 3 weeks, 0.3 µg ibotenic acid was injected into the mediodorsal thalamic nucleus of the midbrain. At 3 or 5 weeks after the initial injury, neuronal discharge in medial prefrontal cortex of rat brain was determined electrophysiologically. The numbers of dopamine-positive neurons and tyrosine hydroxylase immunoreactivity in substantia nigra compacta and ventral tegmental area were detected by immunohistochemical staining. Results demonstrated that after injury, the immunoreactivity of dopamine neurons and tyrosine hydroxylase decreased in the substantia nigra compacta and ventral tegmental areas of rats. Compared with normal medial prefrontal cortical neurons, at 3 and 5 weeks after substantia nigra compacta injury, the discharge frequency of pyramidal neurons increased and the discharge pattern of these neurons tended to be a burst-discharge, with an increased discharge interval. The discharge frequency of interneurons decreased and the discharge pattern also tended to be a burst-discharge, but the discharge interval was only higher at 3 weeks. At 3 weeks after the combined lesions, the discharge frequency, discharge pattern and discharge interval were restored to a normal level in pyramidal neurons and interneurons in medial prefrontal cortex. These findings have confirmed that mediodorsal thalamic nucleus is involved in regulating neuronal activities of the medial prefrontal cortex. The changes in the function of the mediodorsal thalamic nucleus may be associated with the abnormal discharge activity of the medial prefrontal cortex neurons after substantia nigra compacta injury. All experimental procedures were approved by the Institutional Animal Care and Use Committee of Xi'an Jiaotong University, China (approval No. XJTULAC2017-067) on August 26, 2017.

[Effect of 5-HT7 receptor agonist on pyramidal neurons in the medial frontal cortex in a rat model of Parkinson's disease].

OBJECTIVE: To investigate the activity of pyramidal neurons in the medial prefrontal cortex (mPFC) of normal and 6-OHDA-lesioned rats and the responses of the neurons to 5-hydroxytryptamine-7 (5-HT(7)) receptor stimulation. METHODS: The changes in spontaneous firing of the pyramidal neurons in the mPFC in response to 5-HT(7) receptor stimulation were observed by extracellular recording in normal and 6-OHDA-lesioned rats. RESULTS: Both systemic and local administration of 5-HT(7) receptor agonist AS 19 resulted in 3 response patterns (excitation, inhibition and no change) of the pyramidal neurons in the mPFC of normal and 6-OHDA-lesioned rats. In normal rats, the predominant response of the pyramidal neurons to AS 19 stimulation was excitatory, and the inhibitory effect of systemically administered AS 19 was reversed by GABAA receptor antagonist picrotoxinin. In the lesioned rats, systemic administration of AS 19 also increased the mean firing rate of the pyramidal neurons, but the cumulative dose for producing excitation was higher than that in normal rats. Systemic administration of AS 19 produced an inhibitory effect in the lesioned rats, which was partially reversed by picrotoxinin. Local administration of AS 19 at the same dose did not change the ?ring rate of the neurons in the lesioned rats. CONCLUSION: The activity of mPFC pyramidal neurons is directly or indirectly regulated by 5-HT7 receptor, and degeneration of the nigrostriatal pathway leads to decreased response of these neurons to AS 19.

Feasibility study of a partially hollow configuration for zirconia dental implants.

PURPOSE: To assess the feasibility of a new shape configuration involving a partially hollow and porous lower part for dental implants. MATERIALS AND METHODS: Cylindrical zirconia dental implants coated with bioactive glass were fabricated in the laboratory. Each implant has a solid upper part and a partially hollow lower part. It is open at the bottom with holes through the lower cylindrical walls. This hollow and porous configuration permits bone growth into the lower part of the implant that, over time, forms an interlinked network to lock the implant into the alveolar bone. Biomechanical properties of the new design were evaluated through material testing and experiments with dogs. RESULTS: Mechanical testing of bending strength, hardness, fracture toughness, and fatigue life indicated that zirconia implants with the proposed partially hollow configuration can be fabricated to have structural properties comparable to or exceeding the usual requirements for implants. Animal testing suggests that there is appreciable improvement in lock-in strength and osteointegration due to the hollow and porous configuration. CONCLUSION: The new shape configuration is biomechanically feasible and further research is warranted to improve the design for human use.

Poly(brilliant cresyl blue)-carbonnanotube modified electrodes for determination of NADH and fabrication of ethanol dehydrogenase-based biosensor.

A single walled-carbon nanotube (SWNT) modified with poly brilliant cresyl blue (PBCB) glassy carbon electrode has been fabricated by a simple, method in order to facilitate electrocatalytic detection of NADH. At this chemically modified electrode, NADH was determined in neutral phosphate buffer solution at 0V (vs. SCE). The amperometric detection provided a wide linear current vs. concentration range (3.0-104.2 microM), a fast response time (within 5s), high sensitivity [9.89nA (muM)(-1)] and a low detection limit (1.0 microM, S/N=3). No interference was observed with a 100-fold excess of dopamine or uric acid. An ethanol biosensor also was developed using the nanocomposite modified electrode, by immobilizing ethanol dehydrogenase with carrageenan. In this case a linear ethanol concentration response was achieved in the range from 0.4 to 2.4mM and the detection limit was estimated to be 0.1mM (S/N=3). The analytical performance achieved with the of the PBCB/SWNT nanocomposite electrode is expected to the development of novel biosensors, biofuel cells, and other bioelectrochemical devices.

Changes of synaptic structure after long-lasting LTP induced by high and low frequency tetanus in slices of the rat visual cortex.

Synaptic ultrastructural changes after long-lasting long-term potentiation (L-LTP) induced by 2 and 100 Hz tetanus were investigated by electron microscopic and stereological approach in slices of the developing rat visual cortex (postnatal days 15~21). Both 2 and 100 Hz tetanus-induced L-LTP groups showed significant increases in synaptic interface curvature, synaptic numeric density and postsynaptic density thickness, as well as significant decreases in the cleft width, as compared with the control groups. In addition, the volume density of the active zone (AZ) was increased significantly in the 100 Hz tetanus-induced L-LTP group, but not in the 2 Hz group. The mean lateral area of individual AZ in the 100 Hz group was relatively higher than that in the 2 Hz group. These data suggest that newly formed synapses in the 100 Hz tetanus-induced L-LTP group are larger than those in the 2 Hz group and that 100 Hz tetanus might trigger reorganization or synthesis of postsynaptic cytoskeleton.

Changes in the paired-pulse ratio after long-term potentiation induced by 2- and 100-Hz tetanus in rat visual cortical slices.

The effects of 2- and 100-Hz tetanus on long-term potentiation (LTP) of field potentials recorded from layers II/III and induced in layer IV in rat visual cortical slices were examined. Paired-pulse stimulation was used to probe the different mechanisms of LTP induced by 2- and 100-Hz tetanus. The paired-pulse ratio (PPR) decreased after the LTP induced by 2-Hz tetanus, with the changes in PPR being correlated with LTP amplitude. However, in the LTP induced by 100-Hz tetanus, the changes in PPR were not correlated with LTP expression. These experiments suggest that an enhanced probability of presynaptic transmitter release underlies LTP induced by 2-Hz tetanus, but not LTP induced by 100-Hz tetanus.

Different effects of 2 and 100 Hz tetanus on the expression of long-lasting long-term potentiation in rat visual cortical slices.

Long-term potentiation (LTP) can be induced by various tetanic parameters in the mammalian visual cortex. However, little researches have been done on the relationship between the expression of the long-lasting LTP (late phase LTP or L-LTP) lasting more than 3 h and the tetanic parameters. In the present study, the effects of 2 Hz and 100 Hz tetanic parameters on L-LTP of the field potentials were recorded from the layer II/III of the rat visual cortical slices in response to stimulation of the layer IV. As a result, tetanic parameters that had more than 300 pulses reliably induced L-LTP in the postnatal day 15-21 rats. Obviously different L-LTP expressions were induced by 2 Hz and 100 Hz tetani. There was no difference in L-LTP expression induced by the parameters with the same frequency and different total pulses. These data suggest that L-LTPs induced by different frequency parameters may have different induction and maintenance mechanisms; L-LTPs induced by the parameters with the same frequency may have the same mechanisms.

Sexual dimorphism in the induction of LTP: critical role of tetanizing stimulation.

Numerous studies have suggested that sexual dimorphism may exist in learning and memory, particularly in types involving the hippocampus. In the present study, we examined the effects of two different tetani on the induction of long-term potentiation in the CA1 region of hippocampal slices from adult female and male rats to determine the sexual differences in their responses to tetanizing stimulation. We found that the induction of LTP is sex-dependent, and that there were clear sexual differences in the responses to different tetanus patterns, but not impulse number or stimulation frequency. Multiple trains of tetani were more effective in the indution of LTP in male rats than in female ones. These findings suggest that male rats can react to a broader range of tetanizing stimulation compared with female rats. Based on our results and the findings of other studies, we propose that the interaction of gonadal hormones with Ca2+/NMDAR and the subsequent regulation of the ERK/MAP kinase pathway are critical mechanisms for sexual dimorphism in the induction of LTP.

Morphological alteration of the hippocampal synapses in rats prenatally exposed to magnetic resonance imaging magnetic fields.

The present study investigated the effects of prenatal exposure to the magnetic resonance imaging (MRI) magnetic fields on the synaptic ultrastructure of hippocampal formation of rats at different postnatal development stages. Pregnant rats with gestation of 12-18 days were exposed to the magnetic fields used for MRI clinical applications. When the offspring were 1, 2, or 5-month-old, the synaptic morphologic parameters were measured in female offspring. In the 2-month-old MRI group, the curvature of synaptic interface, the length of active zone and the surface density per unit volume (S(v)) of active zone in the dentate gyrus (DG) decreased significantly, and the width of synaptic cleft increased in the CA1 area. In the 5-month-old MRI group, the width of synaptic cleft increased, the thickness of postsynaptic density and the curvature of synaptic interface decreased significantly in the CA1 region, and the width of synaptic cleft increased in the DG. No significant change was observed in the 1-month-old group. These results suggest that prenatal exposure to the medical magnetic fields causes synaptic ultrastructural changes. The relationship of these changes with behavioral impairments was discussed.