Previous results indicate that intra-amygdala infusions of NMDA receptor antagonists block the extinction of conditioned fear. Mitogen-activated protein kinase (MAPK) can be activated by NMDA receptor stimulation and is involved in excitatory fear conditioning. Here, we evaluate the role of MAPK within the basolateral amygdala in the extinction of conditioned fear. Rats received 10 light-shock pairings. After 24 hr, fear was assessed by eliciting the acoustic startle reflex in the presence of the conditioned stimulus (CS) (CS-noise trials) and also in its absence (noise-alone trials). Rats subsequently received an intra-amygdala or intrahippocampal infusion of either 20% DMSO or the MAPK inhibitor PD98059 (500 ng/side) followed 10 min later by 30 presentations of the light CS without shock (extinction training). After 24 hr, they were again tested for fear-potentiated startle. PD98059 infusions into the basolateral amygdala but not the hippocampus significantly reduced extinction, which was otherwise evident in DMSO-infused rats. Control experiments indicated that the effect of intra-amygdala PD98059 could not be attributed to lasting damage to the amygdala or to state dependency. These results suggest that a MAPK-dependent signaling cascade within or very near the basolateral amygdala plays an important role in the extinction of conditioned fear.

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Raf-1, the cellular homolog of the v-raf oncoprotein, is a ubiquitously expressed serine/threonine kinase which serves as a central interface in the transmission of mitogenic signals from the cell membrane to the nucleus. Raf-1 is activated by various growth factors, and its function has been shown to be required for transformation by several classes of oncogenes, including ligands, tyrosine kinase receptors, Ras proteins, and src family tyrosine kinases (recently reviewed in references 18, 50, and 98). Recent investigations have charted a pathway indicating how Raf-1 links membrane-bound signalling molecules to nuclear transcription factors. Upon activation, many growth factor receptors associate with adaptor proteins, such as grb-2, crk, and shc, which in turn recruit guanine nucleotidereleasing proteins (GNRP), such as SOS and C3G, to the plasma membrane. GNRP activate Ras proteins by mediating the exchange of GDP to GTP (29, 62; for reviews, see references 63 and 68). GTP-loaded Ras proteins can bind to the N-terminal region of Raf-1 with high affinity (reviewed in reference 68), causing the translocation of Raf-1 from the cytosol to the membrane, where Raf-1 is exposed to activators (58, 89). The nature of the physiological Raf-1 activator (s) is not yet clear but might include protein kinase C (6, 52, 87) and src family tyrosine kinases (26,60,94,99). Activated Raf-1 in turn can phosphorylate Mek, a dual-specificity kinase which activates the extracellular signal-regulated kinases Erk-1 and -2 by phosphorylation on tyrosine and threonine residues (for reviews, e.g., see references 18, 61, and 98). Activated Erks can translocate to the nucleus and phosphorylate transcription factors. The best-studied nuclear target of Erks is the ternary complex factor, which is required for induction of the c-fos gene (34, 54). The c-Fos protein associates with c-Jun to form the AP-1 transcription factor (reviewed in reference 16), which is a main mediator of v-raf transformation (53,54,73). The activation of this signalling cascade leading from the cell membrane to the nucleus seems to be both necessary and sufficient for transformation of NIH 3T3 fibroblasts (14).A number of recent reports have identified the cyclic AMP (cAMP)-dependent kinase protein kinase A (PKA) as a negative regulator of this pathway. Activation of PKA blocks the activation of Erks in several different cell types, including fibroblasts and smooth muscle cells (4,11,36,38,40,80,91,101). PKA does not affect the activity of Ras, Mek, or mitogenactivated protein kinase (MAPK) (11, 101) but was shown to both inhibit Ras-dependent activation of Raf-1 (4, 11, 101) and downregulate Raf-1 kinase activity directly (38). Phosphorylation of the Raf-1 regulatory domain by PKA decreases the affinity of Raf-1 for activated GTP-loaded Ras, thereby preventing the activation of 101). In addition, phosphorylation of the kinase domain directly suppresses the catalytic activity of the Raf-1 kinase domain (38). This type of inhibition is dominant, as both activated Raf-1...

Neuropathic pain indicates pain caused by damage to the somatosensory system and is difficult to manage and treat. A new treatment strategy urgently needs to be developed. Both autophagy and apoptosis are critical adaptive mechanisms when neurons encounter stress or damage. Recent studies have shown that, after nerve damage, both autophagic and apoptotic activities in the injured nerve, dorsal root ganglia, and spinal dorsal horn change over time. Many studies have shown that upregulated autophagic activities may help myelin clearance, promote nerve regeneration, and attenuate pain behavior. On the other hand, there is no direct evidence that the inhibition of apoptotic activities in the injured neurons can attenuate pain behavior. Most studies have only shown that agents can simultaneously attenuate pain behavior and inhibit apoptotic activities in the injured dorsal root ganglia. Autophagy and apoptosis can crosstalk with each other through various proteins and proinflammatory cytokine expressions. Proinflammatory cytokines can promote both autophagic/apoptotic activities and neuropathic pain formation, whereas autophagy can inhibit proinflammatory cytokine activities and further attenuate pain behaviors. Thus, agents that can enhance autophagic activities but suppress apoptotic activities on the injured nerve and dorsal root ganglia can treat neuropathic pain. Here, we summarized the evolving changes in apoptotic and autophagic activities in the injured nerve, dorsal root ganglia, spinal cord, and brain after nerve damage. This review may help in further understanding the treatment strategy for neuropathic pain during nerve injury by modulating apoptotic/autophagic activities and proinflammatory cytokines in the nervous system.

The loop diuretic bumetanide (Bumex) is thought to have antiepileptic properties via modulate GABAA mediated signaling through their antagonism of cation-chloride cotransporters. Given that loop diuretics may act as antiepileptic drugs that modulate GABAergic signaling, we sought to investigate whether they also affect hippocampal function. The current study was performed to evaluate the possible role of NKCC1 on the hippocampal function. Brain slice extracellular recording, inhibitory avoidance, and western blot were applied in this study. Results showed that hippocampal Long-term potentiation was attenuated by suprafusion of NKCC1 inhibitor bumetanide, in a dose dependent manner. Sequent experiment result showed that Intravenous injection of bumetanide (15.2 mg/kg) 30 min prior to the training session blocked inhibitory avoidance learning significantly. Subsequent control experiment's results excluded the possible non-specific effect of bumetanide on avoidance learning. We also found the phosphorylation of hippocampal MAPK was attenuated after bumetanide administration. These results suggested that hippocampal NKCC1 may via MAPK signaling cascade to possess its function.