Calcium-binding protein, secretagogin, characterizes novel groups of interneurons in the rat striatum.

In the rat striatum numerous secretagogin (SCGN) positive neurons were scattered. They were heterogeneous in their morphological and chemical properties. We examined the colocalization of SCGN with known four interneuron markers, parvalbumin (PV), calretinin (CR), nitric oxide synthase (NOS) and choline acetyl transferase (ChAT). 60-70% of SCGN positive striatal neurons contained either PV or CR or ChAT, but none contained NOS. On the other hand the remaining 30-40% expressed none of these markers, most of which were GAD positive. The present study indicates that there are hitherto unknown groups of striatal interneurons in the rat striatum.

Neurotropin(®) ameliorates chronic pain via induction of brain-derived neurotrophic factor.

Neurotropin (NTP)(®), a non-protein extract isolated from the inflamed skin of rabbits inoculated with vaccinia virus, is used clinically for the treatment of neuropathic pain. Moreover, NTP may activate the descending pain inhibitory system. Depression-like behavior is often complicated by chronic pain. However, little is known about NTP-mediated prevention of mood disorders in chronic pain and its molecular mechanisms. We aimed to investigate the effects of NTP on brain-derived neurotrophic factor (BDNF)-mediated signaling and gene expression in chronic pain. In addition, these effects of NTP were compared with pregabalin which is an anticonvulsant, anxiolytic analgesic used to treat neuropathic pain and fibromyalgia. A chronic constriction injury model was established in Sprague-Dawley rats. The pain response was assessed using a paw withdrawal latency (PWL) test and depression was assessed by the immobility time in a forced swim test (FST). NTP was orally administered in two doses of 50 NU (Neurotropin Unit) and 100 NU/kg for 7 days from day 7 after injury. To measure the analgesic and anti-depressant effects of NTP, either K252a (a tyrosine kinase inhibitor), or 5,7-dihydroxy tryptamine (5,7-DHT, a selective toxin for 5-HTergic neurons) was administered by intracerebroventricular injection. Changes in pERK1/2 and pCREB (immunohistochemistry), 5-HT, and BDNF protein level (ELISA) and BDNF mRNA (RT-PCR) were measured in the anterior cingulate cortex (ACC) and in the rostral ventromedial medulla (RVM) 14 days after injury. After injury, the rats showed a decrease in PWL associated with the increase in time of immobility in FST. In this injury model, NTP blocked both the decrease in PWL and the increase in the FST, while pregabalin (10 mg/kg, po.) did not affect the increase in the FST. These effects of NTP were reversed by K252a, and 5,7-DHT. The analgesic effects of pregabalin were not reversed by K252a. NTP normalized the injury-induced excessive activation of pERK1/2 associated with decreased pCREB and BDNF mRNA in the ACC and in the RVM, and these changes were reversed by 5,7-DHT. In contrast, pregabalin did not affect either pCREB or BDNF levels in the chronic pain model. NTP ameliorated chronic pain and pain-related depression by normalizing the induction of BDNF associated with the 5-HTergic system. Pregabalin showed the analgesic effects but had no effects on either depression or the BDNF pathway. These results suggest that NTP may represent an additional drug strategy for chronic pain associated with depression.

Imipramine ameliorates pain-related negative emotion via induction of brain-derived neurotrophic factor.

Depression-like behavior is often complicated by chronic pain. Antidepressants including imipramine (IMI) are widely used to treat chronic pain, but the mechanisms are not fully understood. Brain-derived neurotrophic factor (BDNF) is a neuromodulator that reduces depression by regulating synaptic transmission. We aimed to characterize the antidepressant effects of IMI without analgesia based on BDNF (trkB)-mediated signaling and gene expression in chronic pain. A chronic constriction injury (CCI) model was constructed in Sprague-Dawley (SD) rats. IMI (5 mg/kg, i.p.) was administered from day 10 after CCI. The pain response was assessed using the paw withdrawal latency (PWL) and depression was judged from the immobility time in a forced swim test. Anti-BDNF antibody, K252a, or 5,7-dihydroxytryptamine (5,7-DHT) were used to examine the antidepressant effects of imipramine. Changes in pERK1/2 (immunohistochemistry), 5-HT and BDNF (ELISA), and BDNF mRNA (RT-PCR) were measured in the anterior cingulate cortex (ACC), rostral ventromedial medulla (RVM), and spinal cord. After CCI, rats showed decreased PWL and increased immobility time. A low dose of IMI reduced the immobility time without having analgesic effects. This antidepressant effect was reversed by anti-BDNF antibody, K252a, and 5,7-DHT. IMI reduced excessive activation of pERK1/2 associated with decreased pCREB and BDNF mRNA, and these changes were reversed by 5,7-DHT. These results show that IMI reduces pain-related negative emotion without influencing pain and that this effect is diminished by denervation of 5-HT neurons and by anti-BDNF treatment. IMI also normalizes derangement of ERK/CREB coupling, which leads to induction of BDNF. This suggests a possible interaction between 5-HT and BDNF.

4-Methylcatechol prevents derangements of brain-derived neurotrophic factor and TrkB-related signaling in anterior cingulate cortex in chronic pain with depression-like behavior.

Chronic pain with mood disorder, resulting from a peripheral nerve injury, is a serious clinical problem affecting the quality of life. A lack of brain-derived neurotrophic factor (BDNF) and abnormal intercellular signaling in the brain can mediate this symptom. BDNF is induced in cultured neurons by 4-methylcatechol (4-MC), but little is known about its role in pain-emotion. Thus, we characterized the actions of 4-MC on TrkB receptor-related pERK and BDNF mRNA in discreet brain regions related to pain-emotion after chronic pain in rat. Rats implanted with a stainless steel cannula into the lateral ventricular were subjected to chronic constriction injury (CCI). Pain was assessed by changes in paw withdrawal latency (PWL) to heat stimuli after CCI. Immobility time during the forced swimming testing was measured for depression-like behavior. Analgesic and antidepression modulations with 4-MC were examined by an anti-BDNF antibody (K252a, a TrkB receptor inhibitor). The animals were perfused and fixed (4% paraformaldehyde) for immunohistochemistry analysis (c-FOS/pERK). BDNF mRNA expression (anterior cingulate cortex) was determined using reverse transcription-PCR. Rats showed a sustained decrease in PWL, associated with a prolonged immobility time after CCI. 4-MC reduced decreases in PWL and increased immobility time. 4-MC reduced increases in pERK immunoreactivity and decreases in BDNF mRNA expression in regions related to pain and the limbic system. Anti-BDNF blocked effects induced by 4-MC. We suggest that a lack of BDNF associated with activated extracellular signal-regulated kinase in the pain-emotion network may be involved in depression-like behavior during chronic pain. 4-MC ameliorates pain-emotion symptoms by inducing BDNF and normalizing pERK activities.

Intracerebroventricular 4-methylcatechol (4-MC) ameliorates chronic pain associated with depression-like behavior via induction of brain-derived neurotrophic factor (BDNF).

Neuropathic pain concurrent with mood disorder from peripheral nerve injury is a serious clinical problem that significantly affects quality of life. Recent studies have suggested that a lack of brain-derived neurotrophic factor (BDNF) in the limbic system may cause this pain-emotion. BDNF is induced in cultured neurons by 4-methylcatechol (4-MC), but the role of 4-MC-induced BDNF in pain-emotion is poorly understood. Thus, we assessed the possible involvement of BDNF in brain in depression-like behavior during chronic pain following peripheral nerve injury. In addition, we examined whether intracerebroventricular (i.c.v.) 4-MC prevents chronic pain in rats and produces an antidepressant effect. Sprague-Dawley rats implanted intracerebroventricularly with a PE-10 tube were subjected to chronic constriction injury (CCI). Pain was assessed by a reduction in paw withdrawal latency (PWL) to heat stimuli after CCI. We also used a forced swimming testing (FST; time of immobility, in seconds) from day 14 to day 21 after CCI. Modulation of pain and emotional behavior was performed by injection of PD0325901 (a MEK1/2 inhibitor). 4-MC (100 nM) was continuously administered i.c.v. for 3 days during the period from day 14 to day 21 after CCI. To block analgesic and antidepressant effects, anti-BDNF antibody or K252a (a TrkB receptor inhibitor) was injected in combination with 4-MC. Naloxone was also coadministered to confirm the analgesic effect of 4-MC. During the chronic stage after CCI, the rats showed a sustained decrease in PWL (thermal hyperalgesia) associated with extension of the time of immobility (depression-like behavior). PD0325901 significantly reduced the decrease in PWL and the increased time of immobility after CCI. The decreased PWL and increased time of immobility were also reduced by 4-MC and by treatment with an ERK1/2 inhibitor. These effects of 4-MC i.c.v. were reversed by anti-BDNF and K252a. The analgesic effect of 4-MC i.c.v. was also antagonized by naloxone. Based on these results, we suggest that a lack of BDNF and activation of ERK1/2 in the pain-emotion network in the CNS may be involved in depression-like behavior during chronic pain. 4-MC i.c.v. ameliorates chronic pain and depression-like behavior by producing of BDNF and normalization of ERK1/2 activation. Therefore, enhancement of BDNF may be a new treatment strategy for chronic pain associated with depression.

Cutaneous magnetic stimulation reduces rat chronic pain via activation of the supra-spinal descending pathway.

Recent studies have demonstrated that magnetic stimulation (MS) can induce cellular responses such as Ca(2+) influx into the cultured neurons and glia, leading to increased intracellular phosphorylation. We have demonstrated previously that MS reduces rat neuropathic pain associated with the prevention of neuronal degeneration. Thus, we aimed to elucidate the actions of MS in relation to modulation of spinal neuron-glia and the descending inhibitory system in chronic pain. The male SD rats intrathecally implanted with catheters were subjected to sciatic nerve ligation (CCI). MS is a low power apparatus characterized by two different frequencies, 2 KHz and 83 MHz. Rats were given MS to the skin (injured sciatic nerve) for 10 min from the seventh day after CCI. The paw withdrawal latency (PWL) evoked by thermal stimuli was measured for 14 days after CCI. Immunohistochemistry for Iba-1 or GFAP was performed after 4% paraformaldehyde fixation (microscopic analysis). We employed microdialysis for measuring CSF 5-HIAA as a reflection of 5-HT release by MS stimulation. Following CCI, rats showed a decrease in PWL after CCI, and the decrease continued until the 14th day. With MS treatment, the decrease in PWL was reduced during the 10-14 day after CCI. Injection of JNK-1 inhibitors on the 14th day antagonized the analgesic effect of MS. MS also eliminated the CCI-induced decrease in GFAP immunoreactivity. Moreover, MS evoked spinal 5-HT release reflected by increase in spinal 5-HIAA level. Thus, we demonstrate that a novel magnetic stimulator used cutaneously can ameliorate chronic pain by not only preventing abnormal spinal neuron-glia interaction, but also through the activation of the supra-spinal descending inhibitory system.