Effects of different fixatives on the TrkB-immunoreactivity in rat brain

Objective: To find out an effective fixative in immunohistochemistry for high-affinity neurotrophin receptor-tyrosine kinase (Trk) B. Methods: Comparing the results from four groups of adult rats which were fixed by different fixatives before the brain sections were processed for TrkB immunohistochemistry. Results: In the four groups, TrkB immunoreactive cells were observed throughout the whole brain, but the intensity of immunoreactive cells and the background staining exhibited a marked difference among the groups. Conclusion: Using 0.3%-0.5% paraformaldehyde in 75% saturated picric acid 0.1 mol/L di-sodium hydrogen phosphate buffer as the fixative may yield the best quality of TrkB immunoreactivity.

Neurons expressing distinct receptors in ventral lateral periaqueductal gray exhibit different modulatory roles in pain and itch sensation

Ventral lateral periaqueductal gray(vIPAG)is an essential transmit node in descending transmission pathway.However,whether neurons expressing different receptors in vIPAG paly distinct roles in nociception and pruriception remains elusive.To evaluate the possible effects of different neuroactive substances in vlPAG,cannula was implanted in the right side of the vIPAG.In the present study,a-amino 3-hydroxy-5-methyl-4-isoxazole-propionic acid(AMPA)receptor antagonist CNQX,N-methyl-D-aspartic acid(NMDA)receptor antagonist AP-5,Y-aminobutyric acid A(GABAs)receptor antagonist picrotoxin(PTX),μ-opioid receptor antagonist CTOP and calcitonin gene-related peptide(CGRP)antagonist CGRP8-37 were utilized.

Potentiation of the lateral habenula-ventral tegmental area pathway underlines the susceptibility to depression in mice with chronic pain

Chronic pain often develops severe mood changes such as depression.However,how chronic pain leads to depression remains elusive and the mechanisms determining individuals’responses to depression are largely unexplored.Here we found that depression-like behaviors could only be observed in 67.9%of mice with chronic neuropathic pain,leaving 32.1%of mice with depression resilience.We determined that the spike discharges of the ventral tegmental area(VTA)-projecting lateral habenula(LHb)glutamatergic(Glu)neurons were sequentially increased in sham,resilient and susceptible mice,which consequently inhibited VTA dopaminergic(DA)neurons through a LHbGlu-VTAGABA-VTADA circuit.Furthermore,the LHbGlu-VTADA excitatory inputs were dampened via GABAB receptors in a pre-synaptic manner.Regulation of LHb-VTA pathway largely affected the development of depressive symptoms caused by chronic pain.Our study thus identifies a pivotal role of the LHb-VTA pathway in coupling chronic pain with depression and highlights the activity-dependent contribution of LHbGlu-to-VTADA inhibition in depressive behavioral regulation.

Co-existence of calcium-binding proteins and γ-aminobutyric acid or glycine in neurons of the rat medullary dorsal horn

Background We investigated the co-expression of calb indin-D28k (CB), calretinin (CR) and parvalbumin (PV, a combination of the three is referred to as CaBPs) with γ-aminobutyric acid (GABA) or glycine in neurons of the rat medullary dorsal horn (MDH).Methods Immunofluorescence histochemical double-staining for CaBPs and GABA or glycine was performed on the sections from rat MDH. Results CB-, CR-, PV-, GABA- and glycine-like immunoreactive (LI) neurons were differentially observed in all layers of the MDH, but particularly in lamina Ⅱ. Neurons that exhibited immunoreactivity for both CaBPs and GABA or glycine were also observed mainly in lamina Ⅱ. A few of them were found in laminae I and III. The percentages of neurons which co-expressed CB/GABA or CB/glycine out of the total numbers of CB- and GABA-LI neurons or CB- and glycine-LI neurons were 5.3% and 12.1% or 4.1% and 10.0%, respectively. The ratios of CR/GABA or CR/glycine co-existing neurons out of the total numbers of CR- and GABA-LI neurons or CR- and glycine-LI neurons were 5.8% and 7.6% or 4.4% and 7.1%, respectively. The rates of PV/GABA or PV/glycine co-localized neurons out of the total numbers of PV- and GABA-LI neurons or PV- and glycine-LI neurons were 11.1% and 5.1% or 9.9% and 5.1%, respectively. Conclusion The results indicate that some neurons in the MDH contain both CaBPs and GABA or glycine.

Inflammation unmasks gabapentin' s effect on AS-fiber evoked excitatory postsynaptic currents in substantia gelatinosa neurons of rat spinal cord

Objective To study the analgesic mechanism of gabapentin, an anticonvulsant, during antinociceptive clinical treatment.Methods Whole-cell voltage-clamp recordings were taken from adult rat spinal cord slices to investigate the effect of gabapentin on primary afferent A8-fiber evoked excitatory postsynaptic currents (EPSCs) to substantia gelatinosa (SG) neurons in normal and inflamed (established by plantar injection of carrageenan) rats.Results Gabapentin (5 -20 μmol/L for 5 min) depressed dorsal root A8 fiber evoked polysynaptic, but not monosynaptic EPSCs to SG experiencing inflammation by about 25% (n = 10, P <0. 01). However, gabapentin did not depress the evoked polysynaptic or monosynaptic EPSCs in normal rats. Gabapentin failed to block a glutamate receptor subtype, N-methyl-D-aspartate (NMDA), -induced slow excitatory currents on SG neurons.Conclusions Inflammation, at least in pan', unmasks the gabapentin depression on nociception transmission in the dorsal horn, and this depression is not due to the blockade of postsynaptic NMDA receptor.