Mechanisms of memory stabilization: are consolidation and reconsolidation similar or distinct processes?

Consolidation of new memories depends on a crucial phase of protein synthesis. It is widely held that, once consolidated, memories are stable and resilient to disruption. However, established memories become labile when recalled and require another phase of protein synthesis to be maintained. Therefore, it has been proposed that when a memory is reactivated it must undergo additional consolidation (reconsolidation) to persist. To determine whether reconsolidation recapitulates consolidation, in the past few years several groups have investigated whether the same molecules and pathways mediate the formation of a memory and its maintenance after reactivation. At first glance, the results appear conflicting: although both processes appear to engage the same molecules and mechanisms, brain areas involved in consolidation after initial training are not required for reconsolidation. In addition, the formation of a memory and its maintenance after reactivation seem to have distinctive temporal molecular requirements. This review concludes with a working model that could explain the apparent controversy of memory vulnerability after reactivation.     

Operative treatment of hangman's fractures of C2. Posterior direct pars screw repair or anterior plate-cage stabilization?

BACKGROUND AND PURPOSE: Feasibility study and evaluation of complications of two different C1-C2 motion-sparing surgical methods for hangman's fracture of C2. MATERIAL AND METHODS: From 2001 till 2005, seventeen patients were operated on because of unstable type II (according to Effendi) hangman's fractures. The patients were treated either with transoral C2-C3 discectomy with plate-cage stabilization or with posterior direct pars screw repair. The plate-cage group (n=9) comprised patients with a mean age of 34 years, and the average follow-up was 42 months. The screw repair group (n=8) included patients with a mean age of 27 years, and the average follow-up was 28 months. X-rays and computed tomography of the spine were performed before the surgery. X-rays were also performed 2 or 3 days after the surgery, during the 6th week after the surgery as well as at 3, 6, 12, and 24 months thereafter. Fusion and stability of C2 were confirmed on flexion-extension X-rays 6 months after the surgery. RESULTS: In all patients C1-C2 motion was preserved and bone fusion with good cervical spine alignment was achieved. In the plate-cage group, an extension of the head that is needed to reduce flexion types of fracture can cause technical difficulties with the correct plate-cage installation because of interference of the jaw and tongue in the operative field. One patient of the group experienced a chronic infection which was resolved by plate-cage removal. Patients in the screw repair group healed uneventfully without complications. CONCLUSIONS: Anterior transoral plate-cage stabilization is indicated for type II fracture with extension displacement and posterior direct pars screw repair for flexion displacement. Nevertheless, posterior direct pars screw repair seems to be safer, cheaper and more technically feasible.     

Effects of (−)-OSU6162 and ACR16 on motor activity in rats,indicating a unique mechanism of dopaminergic stabilization

Dopaminergic stabilizers can be defined as drugs that stimulate or inhibit dopaminergic signalling depending on the dopaminergic tone. (-)-OSU6162 and ACR16 appear to possess such a profile. They have been proposed to act as partial dopamine receptor agonists or as antagonists with preferential action on dopaminergic autoreceptors. Previous studies have shown either stimulation or inhibition of behaviour in response to (-)-OSU6162 and ACR16, which has been suggested to reflect their dual effects on dopaminergic signalling. The aims of the present work are to (1) examine the relation between behavioural response to these drugs and activity baseline, and (2) test the suggested mechanisms of action by means of close comparisons with the known partial D2-receptor agonists (-)-3-PPP and aripiprazole, and the D2 autoreceptor preferring antagonist amisulpride with respect to effects on behaviour. From the results of these experiments it can be concluded that: (1) The direction of the response to (-)-OSU6162 and ACR16 is dependent on activity baseline, which in turn, under physiological conditions, is determined primarily by test arena size of and degree of habituation to the environment. (2) The effects of (-)-OSU6162 and ACR16 cannot be explained on the basis of either partial dopamine receptor agonism or preferential dopamine autoreceptor antagonism. Nevertheless, the current data suggest at least two different D2-receptor-associated targets which mediate opposite effects on activity. This result fits in with a mechanism proposed from a recent in vitro study, according to which (-)-OSU6162 has a dual action on dopamine D2 receptors, (a) an allosteric effect causing an enhanced response to dopamine, and (b) the previously proposed orthosteric effect antagonizing the action of dopamine.