Anisomycin pre-treatment blocked this effect when tested 4 min poststimulation. is usually compared to models of electroconvulsive seizures and fragile X syndrome associated with enhanced mRNA/protein levels and cognitive deficits. and genes at much lower ML-3043 doses than required for protein synthesis inhibition (Mahadevan & Edwards, 1991). This obtaining suggested that PSI-induced gene superinduction and translational arrest are dissociable, impartial effects of PSI. 3.2. Time-scale of action Whereas maximal decrease of protein synthesis resulting from PSI-induced translational arrest occurs within 1-2 hr postinjection (Flood, Rosenzweig, Bennett, & Orme, 1973), gene superinduction characteristically extends beyond several hours after PSI application (Fort et al., 1987; Greenberg, Hermanowski, & Ziff, 1986; Wilson & Treisman, 1988). Thus, the consequences of gene superinduction are likely to outlast those of protein inhibition and thereby dominate the final treatment outcome. 3.3. Desensitization In mammalian cells, pretreatment with anisomycin induces homologous desensitization of intracellular signaling and expression of several genes (mRNA superinduction in the cortex and some hipocampal areas and a decrease in dentate granule cells (Wallace, Lyford, Worley, & Steward, 1998). It appears therefore that this response to PSI is usually highly regulated within specific cell types. Table 1 PSI-induced signaling and gene superinduction in different cell types. (Guzowski, 2002), (Platenik, Kuramoto, & Yoneda, 2000), (Kravitz, Meyer, Seeman, Greendale, & Sowers, 2006), (Melnikova, Savonenko, Wang, Liang, Hand, Wu, Kaufmann, Vehmas, & Andreasson, 2006), (Petitto, McNamara, Gendreau, Huang, & Jackson, 1999) and (Fischer, Sananbenesi, Schrick, Spiess, & Radulovic, 2004) genes. Although memory studies predominantly employed loss-of-function pharmacological and genetic manipulations, superinduction would rather indicate a dysregulated pattern of the expression of a particular gene exceeding the constraints for specific actions required for memory processes. 5. PSI-induced Synaptic Alterations The effects of PSI on morphological changes of neurons have not been studied extensively, and the existing data are somewhat variable most likely due to differences in experimental conditions. In cultured Aplysia sensorimotor synapses anisomycin did not block the formation of functional synapses within 1 hr after cell contact (Coulson & Klein, 1997) but prevented neurotransmitter-induced changes of varicosities of sensory neurons 24 hr posttreatment (Bailey, Montarolo, Chen, Kandel, & Schacher, 1992). Similarly, in rat pyramidal neurons of acute hippocampal slices spinogenesis induced by activation of glucocorticoid receptors was not affected by cycloheximide (Komatsuzaki, Murakami, Tsurugizawa, Mukai, Tanabe, Mitsuhashi, Kawata, Kimoto, Ooishi, & Kawato, 2005), however the same PSI prevented spontaneous spine growth up to 1 1 hr after application but not at later time points (Johnson & Ouimet, 2004). The only study performed to date employed tetanic stimulation of the entorhinal cortex, a procedure resulting in significant enlargement of the dendritic spine area and perimeter of the dentate molecular layer of the hippocampus (Fifkova, Anderson, Young, & Van Harreveld, 1982). Anisomycin pre-treatment blocked this effect when tested 4 min poststimulation. Interestingly, 90 min poststimulation, when anisomycin effects on protein synthesis inhibition were expected to decay, spine enlargement not only reappeared but showed a significant enhancement when compared to stimulated hippocampi without PSI treatment. Supporting a PSI-induced superinduction mechanism, abundance and elongation of spines has been also associated ML-3043 with increased protein synthesis rates and synaptic protein levels in models of fragile X syndrome (Irwin, Patel, Idupulapati, Harris, Crisostomo, Larsen, Kooy, Willems, Cras, Kozlowski, Swain, Weiler, & Greenough, 2001; Qin, Kang, Burlin, Jiang, & Smith, 2005). In the latter model elevated protein levels are suggested to contribute to long-term depressive disorder (LTD) without further need for protein synthesis (Nosyreva & Huber, 2006). Analogously, anisomycin produces late phase LTD in cortical slices (Xiong, Kojic, Zhang, Prasad, Douglas, Wang, & Cynader, 2006), a finding that seems more consistent with hyperproduction than reduction of protein levels. It is important to note that despite the increased protein synthesis rate and spine abundance, the cognitive consequences in both models are reflected in significant impairments of memory (Davis & Squire, 1984; Zhao, Toyoda, Ko, Ding, Wu, & Zhuo, 2005) that can be rescued by neurotransmitters (Martinez, Jensen, & McGaugh, 1981; Ventura, Pascucci, Catania, Musumeci, & Puglisi-Allegra, 2004). 6. Implications of PSI-Induced Gene Superinduction for Memory The delayed molecular and structural alterations of neurons based on gene superinduction, suggest that PSI-induced amnesia may. Although memory studies predominantly employed loss-of-function pharmacological and genetic manipulations, superinduction would rather indicate a dysregulated pattern of the expression of a particular gene exceeding the constraints for specific actions required for memory processes. 5. Bennett, & Orme, 1973), gene superinduction characteristically extends beyond several hours after PSI application (Fort et al., 1987; Greenberg, Hermanowski, & Ziff, 1986; Wilson & Treisman, 1988). Thus, the consequences of gene superinduction are likely to outlast those of protein inhibition and thereby dominate the final treatment outcome. 3.3. Desensitization In mammalian cells, pretreatment with anisomycin induces homologous desensitization of intracellular signaling and expression of several genes (mRNA superinduction in the cortex and some hipocampal areas and a decrease in dentate granule cells (Wallace, Lyford, Worley, & Steward, 1998). It appears therefore that the ML-3043 response to PSI is highly regulated within specific cell types. Table 1 PSI-induced signaling and gene superinduction in different cell types. (Guzowski, 2002), (Platenik, Kuramoto, & Yoneda, 2000), (Kravitz, Meyer, Seeman, Greendale, & Sowers, 2006), (Melnikova, Savonenko, Wang, Liang, Hand, Wu, Kaufmann, Vehmas, & Andreasson, 2006), (Petitto, McNamara, Gendreau, Huang, & Jackson, 1999) and (Fischer, Sananbenesi, Schrick, Spiess, & Radulovic, 2004) genes. Although memory studies predominantly employed loss-of-function pharmacological and genetic manipulations, superinduction would rather indicate a dysregulated pattern of the expression of a particular gene exceeding the constraints for specific actions required for memory processes. 5. PSI-induced Synaptic Alterations The effects of PSI on morphological changes of neurons have not been studied extensively, and the existing data are somewhat variable most likely due to differences in experimental conditions. In cultured Aplysia sensorimotor synapses anisomycin did not block the formation of functional synapses within 1 hr after cell contact (Coulson & Klein, 1997) but prevented neurotransmitter-induced changes of varicosities of sensory neurons 24 hr posttreatment (Bailey, Montarolo, Chen, Kandel, & Schacher, 1992). Similarly, in rat pyramidal neurons of acute hippocampal slices spinogenesis induced by activation of glucocorticoid receptors was not affected by cycloheximide (Komatsuzaki, Murakami, Tsurugizawa, Mukai, Tanabe, Mitsuhashi, Kawata, Kimoto, Ooishi, & Kawato, 2005), however the same PSI prevented spontaneous spine growth up to 1 1 hr after application but not at later time points (Johnson & Ouimet, 2004). The only study performed to date employed tetanic stimulation of the entorhinal cortex, a procedure resulting in significant enlargement of the dendritic spine area and perimeter of the dentate molecular layer of the hippocampus (Fifkova, Anderson, Young, & Van Harreveld, 1982). Anisomycin pre-treatment blocked this effect when tested 4 min poststimulation. Interestingly, 90 min poststimulation, when anisomycin effects on protein synthesis inhibition were expected to decay, spine enlargement not only reappeared but showed a significant enhancement when compared to stimulated hippocampi PTP-SL without PSI treatment. Supporting a PSI-induced superinduction mechanism, abundance and elongation of spines has been also associated with increased protein synthesis rates and synaptic protein levels in models of fragile X syndrome (Irwin, Patel, Idupulapati, Harris, Crisostomo, Larsen, Kooy, Willems, Cras, Kozlowski, Swain, Weiler, & Greenough, 2001; Qin, Kang, Burlin, Jiang, & Smith, 2005). In the latter model elevated protein levels are suggested to contribute to long-term depression (LTD) without further need for protein synthesis (Nosyreva & Huber, 2006). Analogously, anisomycin produces late phase LTD in cortical slices (Xiong, Kojic, Zhang, Prasad, Douglas, Wang, & Cynader, 2006), a finding that seems more consistent with hyperproduction than reduction of protein levels. It is important to note that despite the increased protein synthesis rate and spine abundance, the cognitive consequences in both models are reflected in significant impairments of memory (Davis & Squire, 1984; Zhao, Toyoda, Ko, Ding, Wu, & Zhuo, 2005) that can be rescued by neurotransmitters (Martinez, Jensen, & McGaugh, 1981; Ventura, Pascucci, Catania, Musumeci, & Puglisi-Allegra, 2004). 6. Implications of PSI-Induced Gene Superinduction for Memory The delayed molecular and structural alterations of neurons based on gene superinduction, suggest that PSI-induced amnesia may originate in the hyperproduction of specific proteins rather than inhibition of global protein synthesis. Acting through this mechanism, PSI might trigger a random or erratic formation of neuronal connections that lack input/output.