␤-Amyloid protein is thought to underlie the neurodegeneration associated with Alzheimer's disease by inducing Ca 2؉ -dependent apoptosis. Elevated neuronal expression of the proinflammatory cytokine interleukin-1␤ is an additional feature of neurodegeneration, and in this study we demonstrate that interleukin-1␤ modulates the effects of ␤-amyloid on Ca 2؉ homeostasis in the rat cortex. ␤-Amyloid-(1-40) (1 M) caused a significant increase in 45 Ca 2؉ influx into rat cortical synaptosomes via activation of L-and N-type voltage-dependent Ca 2؉ channels and also increased the amplitude of N-and P-type Ca 2؉ channel currents recorded from cultured cortical neurons. In contrast, interleukin-1␤ (5 ng/ml) reduced the 45 Ca 2؉ influx into cortical synaptosomes and inhibited Ca 2؉ channel activity in cultured cortical neurons. Furthermore, the stimulatory effects of ␤-amyloid protein on Ca 2؉ influx were blocked following exposure to interleukin-1␤, suggesting that interleukin-1␤ may govern neuronal responses to ␤-amyloid by regulating Ca 2؉ homeostasis.␤-Amyloid (A␤-(1-40)) 1 is a peptide fragment derived from proteolytic processing of ␤-amyloid precursor protein (␤APP) (1), which accumulates as an insoluble extracellular deposit around neurons, giving rise to the senile plaques associated with Alzheimer's disease (AD) (2). Increased neuronal expression of the proinflammatory cytokine interleukin-1␤ (IL-1␤) is an additional neuropathological hallmark of AD (3), and inflammatory mediators such as IL-1␤ have been proposed to contribute to the development of amyloid plaques (4). Several reports describe an interaction between IL-1␤ and A␤ at the processing level; IL-1-immunoreactive microglia are prominent components of amyloid plaques in AD (4), and ␤-amyloid promotes release of IL-1␤ by the glial cells that surround senile plaques (5). In turn, IL-1␤ increases ␤APP mRNA expression (6) and promotes processing of ␤APP to liberate A␤ peptide fragments (7). Thus a chain of events involving IL-1␤ and A␤ is involved in plaque formation; however, the nature of the interaction between IL-1␤ and A␤ at a physiological level is poorly understood. Neuronal apoptosis is the suspected causative factor of neurodegeneration in AD, and A␤ fragments have been shown to promote apoptosis in vitro in human-derived neurotypic cells (8) and cultured neurons (9). The mechanism underlying A␤-induced apoptosis is thought to involve disregulation of Ca 2ϩ homeostasis (10). In the C6 glial cell line, expression of the Ca 2ϩ -binding protein calbindin was found to suppress A␤-induced apoptosis (11), providing evidence for the involvement of Ca 2ϩ fluxes in A␤-induced apoptosis. In this study we report that A␤-(1-40) (i) promotes a stimulation of 45 Ca 2ϩ influx into cortical synaptosomes via activation of L-and N-type voltagedependent Ca 2ϩ channels (VDCCs) and (ii) increases the amplitude of N-and P-type VDCC current in cultured cortical neurons. Furthermore, the A␤-(1-40)-induced increase in Ca 2ϩ influx is blocked by the proinflammatory mediato...