Fabio Rupp

The involvement of cAMP-responsive element-binding protein (CREB) signaling in tissue injury-induced inflammation and hyperalgesia has been characterized by measuring phosphorylation of CREB at serine-133 (CREB Ser133) using a specific antibody. In the unstimulated state, unphosphorylated CREB was observed in most nuclei of spinal neurons except for motor neurons, where only a small portion of neurons were stained. A few dorsal root ganglion (DRG) neurons were also CREB-positive. After a unilateral injection of formalin into the hindpaw, a strong and bilateral phosphorylation of CREB Ser133 was induced, as assessed by both immunohistochemistry and Western blot. PhosphoCREB (pCREB)-positive neurons were found in laminae I, II, V, and X of spinal cord on both sides. CREB phosphorylation was very rapid and reached peak levels within 10 min of formalin treatment, whereas few pCREB-positive neurons were seen in unstimulated spinal cord. The induction of pCREB was predominantly postsynaptic, because only 5% of DRG neurons were labeled after inflammation. In contrast to CREB phosphorylation, the induction of c-Fos expression reached peak levels 2 hr after formalin treatment and c-Fos induction was mainly ipsilateral. Both formalin-evoked CREB phosphorylation and c-Fos expression in the spinal cord were suppressed by pretreatment with the NMDA receptor antagonist MK-801 (3.5 mg/kg, i.p.) or halothane anesthesia. These results suggest that CREB signaling may play a role in the long-term facilitation of spinal cord neurons after hyperalgesia. Furthermore, our results indicate that CREB phosphorylation may be necessary but not sufficient for c-fos induction.

Repetitive transcranial magnetic stimulation (rTMS) is a noninvasive technique to induce electric currents in the brain. Although rTMS is being evaluated as a possible alternative to electroconvulsive therapy for the treatment of refractory depression, little is known about the pattern of activation induced in the brain by rTMS. We have compared immediate early gene expression in rat brain after rTMS and electroconvulsive stimulation, a well-established animal model for electroconvulsive therapy. Our result shows that rTMS applied in conditions effective in animal models of depression induces different patterns of immediate-early gene expression than does electroconvulsive stimulation. In particular, rTMS evokes strong neural responses in the paraventricular nucleus of the thalamus (PVT) and in other regions involved in the regulation of circadian rhythms. The response in PVT is independent of the orientation of the stimulation probe relative to the head. Part of this response is likely because of direct activation, as repetitive magnetic stimulation also activates PVT neurons in brain slices.