Effects of stress memory by fear conditioning on nerve-mast cell circuit in skin

Inflammatory skin disorder aggravates when a horrific memory is evoked, but the mechanism of this effect is unclear. The objective of the present study was to examine the effects of evocation of a horrific memory on the skin and mast cells in an animal model. A sound stimulus linked to an electric shock was given to C57BL/6 mice (7-week old, males). One, 3 and 5 days later, the mice received the sound stimulus again. The reactions of mice that received the initial sound stimulus were compared with those of mice that did not receive the initial stimulus. A freezing phenomenon was observed when the sound stimulus was given to mice that received the initial stimulus, which indicated evocation of a past memory of fear. The degranulation rate of dermal mast cells and the length of substance P (SP)-positive nerve fibers of the skin significantly increased on days 1 and 3, the SP level decreased significantly, and the number of SP-expressing cells in the dorsal root ganglion significantly increased on day 1. These findings suggest that prior experience of severe stress linked to a stimulus subsequently evokes fear associated with the same stimulus and results in activation of dermal mast cells and skin nerves.

Chronic stress enhances synaptic plasticity due to disinhibition in the anterior cingulate cortex and induces hyper-locomotion in mice

The anterior cingulate cortex (ACC) is involved in the pathophysiology of a variety of mental disorders, many of which are exacerbated by stress. There are few studies, however, of stress-induced modification of synaptic function in the ACC that is relevant to emotional behavior. We investigated the effects of chronic restraint stress (CRS) on behavior and synaptic function in layers II/III of the ACC in mice. The duration of field excitatory postsynaptic potentials (fEPSPs) was longer in CRS mice than in control mice. The frequency of miniature inhibitory postsynaptic currents (mIPSCs) recorded by whole-cell patch-clamping was reduced in CRS mice, while miniature excitatory postsynaptic currents (mEPSCs) remained unchanged. Paired-pulse ratios (PPRs) of the fEPSP and evoked EPSC were larger in CRS. There was no difference in NMDA component of evoked EPSCs between the groups. Both long-term potentiation (LTP) and long-term depression of fEPSP were larger in CRS mice than in control mice. The differences between the groups in fEPSP duration, PPRs and LTP level were not observed when the GABA(A) receptor was blocked by bicuculline. Compared to control mice, CRS mice exhibited hyper-locomotive activity in an open field test, while no difference was observed between the groups in anxiety-like behavior in a light/dark choice test. CRS mice displayed decreased freezing behavior in fear conditioning tests compared to control mice. These findings suggest that CRS facilitates synaptic plasticity in the ACC via increased excitability due to disinhibition of GABA(A) receptor signalling, which may underlie induction of behavioral hyper-locomotive activity after CRS.

Increase in hemokinin-1 mRNA in the spinal cord during the early phase of a neuropathic pain state

BACKGROUND AND PURPOSE

Substance P (SP), a representative member of the tachykinin family, is involved in nociception under physiological and pathological conditions. Recently, hemokinin-1 (HK-1) was identified as a new member of this family. Although HK-1 acts on NK(1) tachykinin receptors that are thought to be innate for SP, the roles of HK-1 in neuropathic pain are still unknown.

EXPERIMENTAL APPROACH

Using rats that had been subjected to chronic constrictive injury (CCI) of the sciatic nerve as a neuropathic pain model, we examined the changes in expression of SP- and HK-1-encoding genes (TAC1 and TAC4, respectively) in the L4/L5 spinal cord and L4/L5 dorsal root ganglia (DRGs) in association with changes in pain-related behaviours in this neuropathic pain state.

KEY RESULTS

The TAC4 mRNA level was increased on the ipsilateral side of the dorsal spinal cord, but not in DRGs, at day 3 after CCI. In contrast, the TAC1 mRNA level was significantly increased in the DRGs at day 3 after CCI without any changes in the dorsal spinal cord. Analysis of a cultured microglial cell line revealed the presence of TAC4 mRNA in microglial cells. Minocycline, an inhibitor of microglial activation, blocked the increased expression of TAC4 mRNA after CCI and inhibited the associated pain-related behaviours and microglial activation in the spinal cord.

CONCLUSIONS AND IMPLICATIONS

The present results suggest that HK-1 expression is increased at least partly in activated microglial cells after nerve injury and is clearly involved in the early phase of neuropathic pain.

Low serum levels of brain-derived neurotrophic factor and epidermal growth factor in patients with chronic schizophrenia

Neurotrophic factors (NFs) play a pivotal role in the development of the central nervous system. They are thus also suspected of being involved in the etiology of schizophrenia. Previous studies reported a decreased level of serum brain-derived neurotrophic factor (BDNF) in schizophrenia, whereas the association of epidermal growth factor (EGF) with this illness remains controversial. Using a two-site enzyme immunoassay, we conducted the simultaneous measurement of serum BDNF and EGF levels in a group of patients with chronic schizophrenia (N=74) and a group of normal controls matched in age, body mass index, smoking habit and sex (N=87). We found that, compared to normal controls, patients with chronic schizophrenia exhibited lower serum levels of both BDNF and EGF across all ages examined (21-59 years). The serum levels of BDNF and EGF were negatively correlated in the controls (r=-0.387, P=0.0002) but not in the patients. Clinical parameters such as duration of illness and psychiatric rating scale also showed no robust correlations with the NF levels. Collectively, these results suggest that pervasive, abnormal signaling of NFs underlies the pathophysiology of chronic schizophrenia.

Effect of duration of in vitro maturation on nuclear maturation and fertilizability of feline oocytes

This study was conducted to improve in vitro production of embryos from domestic cats using TCM-199 as an IVM medium. The time sequence of nuclear maturation and the optimal timing of in vitro insemination were examined. Most oocytes were at the germinal vesicle stage immediately after collection; however, 8.3% had already resumed meiosis before IVM culture. After 30 h of IVM culture, the percentage of oocytes at metaphase II (MII) reached a peak (75.5%) and did not change (P>0.05) from 30 to 48 h after IVM culture. The percentage of oocytes with two pronuclei was higher (P<0.05) for oocytes matured for 30 and 36 h (38.2 and 33.0%, respectively) than for those after IVM culture for only 24 h (18.5%). Total sperm penetration rate was highest (P<0.05) for oocytes that had been matured for 30 h (46.1%). After 30 h of IVM and 18 h of IVF culture, 66.3 and 24.8% of inseminated oocytes had cleaved and developed to the blastocyst stage, respectively. We concluded that IVM of feline oocytes for 30 h in TCM-199 resulted in optimal nuclear maturation and sperm penetration.

Dynamic changes in nerve growth factor and substance P in the murine hair cycle induced by depilation

Increasing evidence suggests that various neurotrophins and neuropeptides play an important role in the progression of hair follicle cycling. Among them, nerve growth factor (NGF) and substance P (SP) have attracted special interest recently. However, the interaction between these factors during hair cycling has not yet been systematically studied. We therefore investigated the mutual relationships between NGF and SP and the mechanism by which the anagen stage of the hair cycle is initiated. Fluctuations in numbers of SP-positive nerve fibers and variations in amounts of SP, NGF, and another neurotrophic factor, glial cell-derived neurotrophic factor, in skin in the C57BL/6 mouse depilation-induced hair cycle model, together with the spatiotemporal expression patterns of each of these factors, were followed simultaneously by enzyme-linked immunosorbent assay and immunohistochemistry. The main finding was that a surge in NGF expression and a rapid increase in NGF content in skin is an initial event within 1 day after depilation, followed by elevation of SP content and numbers of SP-containing fibers 2 days after the increase in NGF. Our findings suggest that a rapid and abundant increase in NGF plays a key role in the induction and progression of anagen hair cycling through keratinocyte growth promotion. NGF may also induce plastic changes such as sprouting and hyperplasia in dermal nerve fibers and enhance their SP production. Elevated levels of SP in skin may additionally contribute to the progression of consecutive anagen hair cycles.

Distribution and pharmacological characterization of primate NK-1 and NK-3 tachykinin receptors in the central nervous system of the rhesus monkey

Much attention has focused on tachykinin receptors as therapeutic targets for neuropsychiatric disorders, although their expressional distributions in the primate central nervous system (CNS) remain unclear. We cloned the genes encoding the NK-1 and NK-3 tachykinin receptors (referred to as rmNK-1 and rmNK-3) from the rhesus monkey (Macaca mulatta) brain and examined their pharmacological profiles and regional distributions in the CNS. The deduced rmNK-1 amino-acid sequence differed by only two amino acids from the human NK-1 (hNK-1). The deduced rmNK-3 amino-acid sequence was two amino acids shorter than human NK-3 (hNK-3), with a seven-amino-acid difference in sequence. Ligand binding studies revealed that the affinity of rmNK-1 to substance P (SP) was comparable to that of hNK-1 in cell lines that expressed individual receptors stably. Nonpeptide antagonists had similar effects on the binding of rmNK-1 and hNK-1. Affinity of rmNK-3 for NKB was stronger than for SP and the IC50 value was comparable with that of hNK-3. Ca2+ imaging showed that activations of both rmNK-1 and rmNK-3 by specific ligands, SP and senktide, induced increased intracellular Ca2+ in cell lines that stably expressed individual primate tachykinin receptors. The amounts of rmNK-1 and rmNK-3 mRNAs were quantitatively determined in the monkey CNS. The expression of rmNK-1 was observed in all of the cortical and subcortical regions, including the hippocampus and the amygdala. The putamen contained the most NK-1 mRNA in the brain, with less rmNK-3 mRNA found in the cortex compared to rmNK-1 mRNA. In the monkey hippocampus and amygdala, rmNK-1 mRNA was present at markedly higher concentrations than rmNK-3 mRNA. The present results provide an insight into the distinct physiological nature and significance of the NK-1 and NK-3 tachykinin systems in the primate CNS. These findings are indispensable for establishing model systems in the search for a subtype-specific tachykinin receptor agonist and antagonist for the treatment of neuropsychiatric disorders.

Expression changes of cation chloride cotransporters in the rat spinal cord following intraplantar formalin

Cation chloride cotransporters, K(+)-Cl(-) cotransporter 2 (KCC2) and Na(+)-K(+)-Cl(-) cotransporter 1 (NKCC1) are reported to be expressed in the neurons in the spinal cord and regulate intracellular Cl(-) concentration. Evidence has been accumulating that the expression of cation chloride cotransporters changes in inflammatory or neuropathic pain, and such changes take a part in pathophysiology of the persistent pain states. However, it is largely unknown how these cotransporters contribute to hyperalgesia in the acute pain state. We, therefore, investigated expression changes of KCC2 and NKCC1 in the spinal dorsal horn of the rat after the intraplantar injection of formalin as an acute nociceptive stimulus. The rats showed two phases (phases 1 and 2) of increase in pain-related behavior in response to formalin. We found that expression of KCC2-like immunoreactivity (IR) was reduced in lamina I and II in the lumbar spinal cord on the stimulated side in phase 1, and then recovered gradually. In contrast, the number of NKCC1-like IR-positive cells was unchanged over the period examined. These results suggest that KCC2, rather than NKCC1, mainly contributes to modulating excitability of the dorsal spinal cord neurons in the initial stage of formalin-evoked hyperalgesia.

Role of substance P in stress-derived degranulation of dermal mast cells in mice

BACKGROUND

The interaction between nerves and mast cells can effect regulation of the immune system and inflammatory responses. Recent studies have shown that various stressors can induce degranulation of dermal mast cells in animals.

OBJECTIVES

This study was conducted to confirm that substance P (SP) was involved in the degranulation of dermal mast cells in stress conditions.

METHODS

Using a communication box system, foot shock stress (FS) and psychological stress (PS) were administered to mice and the degranulation rate of dermal mast cells, the number of SP-positive nerve fibers and changes in SP content were determined. The inhibitory effect of a non-peptide NK1-receptor antagonist on these changes was investigated.

RESULTS

Both FS and PS significantly enhanced the degranulation of dermal mast cells and increased the number of SP-positive nerve fibers. FS significantly decreased dermal SP content whereas SP was increased by PS. These changes were inhibited by intraperitoneal injection of NK(1) receptor antagonist.

CONCLUSIONS

It was considered that SP released from the nerve ending, had an important role in the degranulation of dermal mast cells. Results of this study suggest that the tachykinin receptor antagonist exhibited an inhibitory effect on aggravated stress-induced dermatitis.