Extensive research has shown that the hippocampus and striatum have dissociable roles in memory and are necessary for "place" and "response" learning, respectively. In the present study, rats were trained on a cross maze task that could be solved by either a place or a response strategy, and the strategy used was determined by a probe trial. Phosphorylated cAMP response element-binding protein (pCREB) and c-Fos immunoreactivity (IR) were measured in the hippocampus and striatum either immediately or 1 hr after cross maze training. Immediately after training, pCREB-IR and c-Fos-IR were significantly higher in the hippocampus and striatum of trained rats than in control rats matched for motor activity, but the increase was independent of the strategy revealed at probe. One hour after training, however, pCREB-IR and c-Fos-IR were sustained in the hippocampal pyramidal and granule cell layers of place learners but returned to basal levels among response learners. In addition, pCREB-IR was sustained in the dorsomedial and dorsolateral striatum of response learners but returned to basal levels among place learners. There were no differences between place and response learners in c-Fos-IR in the striatum at either time point. The present results indicate that cross maze training causes an initial activation of transcription factors in both the hippocampus and striatum. Formation of memory for a place strategy, however, is related to sustained phosphorylation of CREB and expression of c-Fos for at least 1 hr in the hippocampus, whereas formation of memory for a response strategy is related to phosphorylation of CREB in the striatum.
Current theories of neuropathic hypersensitivity include an imbalance of supraspinal inhibition and facilitation. Our overall hypothesis is that the locus coeruleus (LC), classically interpreted as a source of pain inhibition, may paradoxically result in facilitation after tibial and common peroneal nerve transection (spared sural nerve injury – SNI). We first tested the hypothesis that non-noxious tactile hindpaw stimulation of the spared sural innervation territory increases neuronal activity in the LC in male rats. We observed a bilateral increase in the stimulus-evoked expression of transcription factors Fos and phosphorylated CREB (pCREB) in LC after SNI but not sham surgery; these markers of neuronal activity correlated with the intensity of tactile allodynia. We next tested the hypothesis that noradrenergic neurons contribute to the development of neuropathic pain. To selectively destroy these neurons, we delivered anti-dopamine-β-hydroxylase saporin (anti-DβH-saporin) into the intracerebroventricular space two weeks before SNI. We found that anti-DβH-saporin, but not an IgG-saporin control, reduced behavioural signs of tactile allodynia, mechanical hyperalgesia, and cold allodynia from 3-28 d after SNI. Our final experiment tested the hypothesis that the LC contributes to the maintenance of neuropathic pain. We performed SNI, waited two weeks for maximal allodynia and hyperalgesia to develop, and then administered the local anaesthetic lidocaine (4%) directly into the LC parenchyma. Lidocaine reduced all behavioural signs of neuropathic pain in a reversible manner, suggesting that the LC contributes to pain facilitation. We conclude that, in addition to its well-known inhibition of acute and inflammatory pain, the LC facilitates the development and maintenance of neuropathic pain in the SNI model. Further studies are needed to determine the facilitatory pathways emanating from the LC.
Extensive research has shown that the hippocampus is necessary for consolidation of long-term spatial memory in rodents. We reported previously that rats using a place strategy to solve a cross maze task showed sustained phosphorylation of hippocampus cyclic AMP response element-binding protein (CREB), a transcription factor implicated in long-term memory formation. In the current study, we used viral vector-mediated gene transfer to test the hypothesis that formation of long-term memory for place learning can be facilitated by increasing levels of CREB in the dorsal hippocampus. Three days after intrahippocampus infusion, experimental (HSV-CREB) and control (HSV-LacZ; saline) rats were trained during a single session on a place task in a water cross maze. Rats were tested for memory 5 d later. Rats in all groups showed short-term memory, and there were no significant differences among treatment groups during acquisition. However, only HSV-CREB-infused rats showed significant savings between training and test, while HSV-LacZ-and saline-treated rats did not. Quantitative Western blotting confirmed that levels of dorsal hippocampus CREB were increased during training in rats infused with HSV-CREB in comparisons with controls. The present results show that formation of long-term memory can be facilitated by increasing levels of hippocampus CREB protein.At the cellular level, memory is hypothesized to be encoded and stored through activity-dependent changes in synaptic strength (Martin et al. 2000). Long-term memory formation requires de novo protein synthesis that is not necessary for short-term memory (Davis and Squire 1984). The cAMP response elementbinding protein (CREB) is a transcription factor regulated through phosphorylation on Ser133 by stimuli that increase cAMP-or Ca 2+ -dependent protein kinase activity (Gonzalez and Montminy 1989;Dash et al. 1991). Phosphorylated CREB promotes the synthesis of a wide array of proteins implicated in neuronal plasticity (Impey et al. 2004), which makes CREB well suited for regulation of long-term memory formation. Spatial learning increases CREB phosphorylation in the dorsal hippocampus (Mizuno et al. 2002;Colombo et al. 2003), while decreased levels of CREB (Guzowski and McGaugh 1997) or disruption of CREB-dependent transcription (Pittenger et al. 2002) in the dorsal hippocampus interferes with spatial memory.We reported previously that learning-induced increases in phosphorylated CREB were sustained in the hippocampus of rats that use a place strategy to solve a land-based cross maze (Colombo et al. 2003). In the current study, rats were trained during a single session in a water cross maze to escape to a constant location from variable start locations. The training protocol was designed so that rats learned the escape location but did not show long-term memory 5 d after training. Previous work has shown that increasing CREB levels in the basolateral amygdala enhances long-term memory for amygdala-dependent cued fear conditioning (Josselyn et al. 2001). The present exp...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.