Fu-Hua Wang

Galanin Is a Potent In Vivo Modulator of Mesencephalic Serotonergic Neurotransmission

Neurochemical, molecular, immunohistochemical and behavioral methods were used to examine the in vivo effects of the neuropeptide galanin on central 5-HT neurotransmission and on 5-HT1A receptor-mediated responses. Intraventricularly infused galanin caused a long-lasting and dose-dependent reduction of basal extracellular 5-HT levels in the ventral hippocampus of awake rats as measured by microdialysis. Infusion of galanin into the dorsal raphe nucleus (DRN), but not intrahippocampally, reduced 5-HT release. The effect of i.c.v. galanin on 5-HT release was blocked by the galanin receptor antagonist M35, acting most likely via galanin receptors at the level of the DRN. Galanin also reduced the levels of tryptophanhydroxylase mRNA in the DRN. Therefore, the effects of galanin on 5-HT1A receptor-mediated responses were further investigated. Surprisingly, galanin significantly attenuated the reduction of hippocampal 5-HT release induced by systemic injection of the 5-HT1A receptor agonist 8-OH-DPAT. Galanin also attenuated 8-OH-DPAT-induced hypothermia and locomotor activity in rats. These results indicate that galanin has important inhibitory actions on central 5-HT neurotransmission and on 5-HT1A receptor-mediated events.

Galanin Modulates 5‐Hydroxytryptamine Functions: Focus on Galanin and Galanin Fragment/5‐Hydroxytryptamine1A Receptor Interactions in the Braina

Abstract: The reciprocal interactions between galanin and 5‐HT1A receptors in the rat brain are presented. Galanin and its NH2‐terminal fragments antagonize 5‐HT1A receptor‐mediated transmission at the postjunctional level, whereas galanin receptor activation mimics the inhibitory action of 5‐HT1A receptor activation at the soma‐dendritic level, leading to reductions of 5‐HT metabolism and release. These interactions have been shown in both receptor binding studies and functional studies. In view of the present findings, galanin antagonists may represent a new type of antidepressant drug, based on the 5‐HT hypothesis of depression, by enhancing 5‐HT release and postjunctional 5‐HT1A‐mediated transmission. Moreover, following intracerebroventricular injection galanin was found to be internalized in a population of hippocampal nerve cells mainly representing GABA, somatostatin, and/or NPY‐immunoreactive nerve cells. The relevance of these findings is discussed in relation to the concept of volume transmission.

Magnetic resonance tracking of nanoparticle labelled neural stem cells in a rat’s spinal cord

Neural stem cells isolated from an adult rats spinal cord were loaded with superparamagnetic gold-coated monocrystalline iron oxide nanoparticles (Au-MION) intended for use as contrast enhancers in magnetic resonance imaging (MRI). A dose-dependent attenuation of MRI signals was observed for Au-MION down to 0.001 µg Fe/µl and for nanoparticle-loaded clusters of only 20 cells. The labelled cells were infused into the spinal cord of anaesthetized rats and tracked by MRI at 1 h, 48 h and 1 month post-injection. Histological analysis revealed that MRI signals correlated well with gold-positive staining of transplanted cells. The present results show that Au-MION exerts powerful contrast-enhancing properties and may represent novel MRI labels for labelling and tracking the transplanted cells in vivo.

Determination of Conjugation Efficiency of Antibodies and Proteins to the Superparamagnetic Iron Oxide Nanoparticles by Capillary Electrophoresis with Laser-Induced Fluorescence Detection

The method based on capillary electrophoresis with laser-induced fluorescence detection (CE/LIF) was developed for determination of magnetic iron oxide nanoparticles (hydrodynamic diameters of 100 nm) functionalized with molecules containing primary amino groups. The magnetic nanoparticles with carboxylic or aminopropyl-trimethoxysilane groups at their surface were conjugated to the model proteins (bovine serum albumin, BSA; streptavidin or goat anti-rabbit immunoglobulin G, IgG) using carbodiimide as a zero-length cross-linker.The nanoparticle–protein conjugates (hydrodynamic diameter 163–194 nm) were derivatized with naphthalene-2,3-dicarboxaldehyde reagent and separated by CE/LIF with a helium–cadmium laser (excitation at 442 nm, emission at 488 nm). The separations were carried out by using a fused-silica capillary (effective length 48 cm, inner diameter 75 um) and 100 mM sodium borate buffer (pH 9.2), the potential was 30 kV. The detection limit for BSA-conjugate was 1.3 pg/10 nl, i.e. about 20 amol. The present method provides an efficient and fast tool for sensitive determination of the efficacy of biomolecular functionalization of magnetic nanoparticles. The CE/LIF technique requires only negligible sample volumes for analysis, which is especially suitable for controlling the process of preparation of functionalized nanoparticles with unique properties aimed to be used for diagnostic or therapeutic purposes.

Prolonged effects of intraventricular galanin on a 5-hydroxytryptamine1A receptor mediated function in the rat

Galanin (3 nmol/rat), 2 h after its intracerebroventricular (i.c.v.) administration to male rats, attenuated the passive avoidance (PA) retention deficit induced by the 5-hydroxytryptamine (HT)(1A) receptor agonist 8-hydroxy-2-(di-N-propylamino)tetraline (8-OH-DPAT) (0.2 mg/kg) The reduction in the postjunctional 5-HT(1A) receptor-mediated response after i.c.v. galanin was not associated with changes in the mRNA levels and agonist binding properties of cortical limbic 5-HT(1A) receptors, believed to be the target receptors mediating the PA deficit caused by 8-OH-DPAT. These results suggest that acute increases of galanin transmission in vivo even after 2 h can counteract limbic 5-HT(1A) receptor-mediated responses of relevance for affective disorders without significantly affecting gene expression and binding characteristics of cortical limbic 5-HT(1A) receptors.

Local Dopaminergic Modulation of the Motor Activity Induced by N-methyl-D-aspartate Receptor Stimulation in the Ventral Hippocampus

Dopaminergic neurotransmission has been implicated in the motor activating effects induced by the local infusion of NMDA in the ventral hippocampus (VH). The nucleus accumbens and the ventral tegmental area (VTA) have been proposed to be the main loci where dopamine is acting as a positive modulator of the VH NMDA receptor-mediated motor activating effects. However, the existence of a relatively high dopamine innervation and dopamine receptor density in the VH suggests the possibility of local dopamine/NMDA receptor interactions. This hypothesis was tested by studying the effects of the bilateral local VH infusion of NMDA (0.05, 0.1, 0.5 and 1.0 μg/side), the dopamine D1/D5 receptor antagonist SCH 23390 (1 μg/side) and the dopamine D2 receptor antagonist raclopride (1 and 5 μg/side). Neither SCH 23390 nor raclopride induced any significant change in motor activity compared with the vehicle control group, but both compounds significantly antagonized the motor activation induced by NMDA. SCH 23390 (1 μg/side) was more potent that raclopride (minimal effective dose: 5 μg/side). These results demonstrate the existence of a strong tonic facilitating effect of dopamine, acting preferentially at dopamine D1/D5 receptors, on NMDA receptor-mediated effects in the VH.

Effects of the 5-HT1B receptor antagonist NAS-181 on extracellular levels of acetylcholine, glutamate and GABA in the frontal cortex and ventral hippocampus of awake rats: A microdialysis study

The purpose of this study was to investigate the effects of the 5-HT(1B) receptor antagonist NAS-181 ((R)-(+)-2-(3-morpholinomethyl-2H-chromen-8-yl) oxymethyl-morpholine methanesulfonate) on cholinergic, glutamatergic and GABA-ergic neurotransmission in the rat brain in vivo. Extracellular levels of acetylcholine, glutamate and GABA were monitored by microdialysis in the frontal cortex (FC) and ventral hippocampus (VHipp) in separate groups of freely moving rats. NAS-181 (1, 5 or 10 mg/kg, s.c.) caused a dose-dependent increase in ACh levels, reaching the maximal values of 500% (FC) and 230% (VHipp) of controls at 80 min post-injection. On the contrary, NAS-181 injected at doses of 10 or 20 mg/kg s.c. had no effect on basal extracellular levels of Glu and GABA in these areas. The present data suggest that ACh neurotransmission in the FC and VHipp, the brain structures strongly implicated in cognitive function, is under tonic inhibitory control of 5-HT(1B) heteroreceptors localized at the cholinergic terminals in these areas.

Diffusion and clearance of superparamagnetic iron oxide nanoparticles infused into the rat striatum studied by MRI and histochemical techniques

The purpose of the present study was to investigate, by MRI and histochemical techniques, the diffusion and clearance abilities of superparamagnetic iron oxide nanoparticles (SPION) coated with dextran (Dextran-SPION) and gold (Au-SPION) following their local infusions into the rat brain. In separate groups of anesthetized rats, the Dextran-SPION and Au-SPION were infused at concentrations of 0.01, 0.1, 1 and 5 µg Fe/0.5 µl and at the flow rate of 0.5 µl min(-1) into the left and right striata, respectively. Repetitive T2-weighted spin-echo MRI scans were performed at time intervals of 1, 6, 12, 24, 48, 72 h, and one, two and eight weeks after inoculation. Following infusion of Dextran-SPION (0.1 µg and 1 µg Fe), the maximal distribution volume was observed at about 12-24 h after inoculation and two weeks later the Fe signals were undetectable for the lower dose. On the other hand, Au-SPION remained tightly localized in the closest vicinity of the infusion site as revealed by unchanged MRI signal intensities and strong histochemical staining of Fe(2+) and Fe(3+) ions in the corresponding brain slices. Immunohistochemical staining of astrocytic and microglial reactions revealed that there were no marked differences in GFAP, VIM or OX-42 labeling observed between the nanoparticle types, however the astrocytic reaction was more pronounced in rats receiving nanoparticles compared to the control (aCSF-infused) rats. In conclusion, the present data demonstrate that the viral-sized Dextran-SPION were able to diffuse freely through the interstitial space of the brain being progressively cleared out from the infusion site within two weeks. Thus, Dextran-SPION could be beneficially used in MRI-guided diagnostic applications such as in experimental oncology or as labels and carriers for targeted drug delivery, whereas Au-SPION could be used for labeling and tracking the transplanted stem cells in experimental MRI.

The selective 5-HT1A receptor antagonist NAD-299 increases acetylcholine release but not extracellular glutamate levels in the frontal cortex and hippocampus of awake rat

The effects of the HT(1A) receptor antagonist NAD-299 on extracellular acetylcholine (ACh) and glutamate (Glu) levels in the frontal cortex (FC) and ventral hippocampus (HPC) of the awake rats were investigated by the use of in vivo microdialysis. Systemic administration of NAD-299 (0.3; 1 and 3micromol/kg s.c.) caused a dose-dependent increase in ACh levels in FC and HPC (peak value of 209% and 221%, respectively) and this effect was comparable to that induced by donepezil (2.63micromol/kg s.c.). Moreover, the ACh levels in the FC increased even after repeated (14days) treatment with NAD-299 and when NAD-299 was injected locally into the nucleus basalis magnocellularis or perfused through the microdialysis probe implanted in the cortex. In contrast, NAD-299 failed to alter the extracellular levels of glutamate after systemic (3micromol/kg s.c.) or local (100microM) administration. The present data support the hypothesis that cholinergic transmission in cortico-limbic regions can be enhanced via blockade of postsynaptic 5-HT(1A) receptors, which may underlie the proposed cognitive enhancing properties of NAD-299 in models characterized by cholinergic deficit.