Astrocytes respond to a neurotoxic Aß fragment with state-dependent Ca2+ alteration and multiphasic transmitter release.

Excessive amounts of amyloid ß (Aß) peptide have been suggested to dysregulate synaptic transmission in Alzheimer's disease (AD). As a major type of glial cell in the mammalian brain, astrocytes regulate neuronal function and undergo activity alterations upon Aß exposure. Yet the mechanistic steps underlying astrocytic responses to Aß peptide remain to be elucidated. Here by fluorescence imaging of signaling pathways, we dissected astrocytic responses to Aß25-35 peptide, a neurotoxic Aß fragment present in AD patients. In native health astrocytes, Aß25-35 evoked Ca2+ elevations via purinergic receptors, being also dependent on the opening of connexin (CX) hemichannels. Aß25-35, however, induced a Ca2+ diminution in Aß-preconditioned astrocytes as a result of the potentiation of the plasma membrane Ca2+ ATPase (PMCA). The PMCA and CX protein expression was observed with immunostaining in the brain tissue of hAPPJ20 AD mouse model. We also observed both Ca2+-independent and Ca2+-dependent glutamate release upon astrocytic Aß exposure, with the former mediated by CX hemichannel and the latter by both anion channels and lysosome exocytosis. Our results suggest that Aß peptide causes state-dependent responses in astrocytes, in association with a multiphasic release of signaling molecules. This study therefore helps to understand astrocyte engagement in AD-related amyloidopathy.

Incubation of Cocaine Craving After Intermittent-Access Self-administration: Sex Differences and Estrous Cycle.

BACKGROUND: Studies using continuous-access drug self-administration showed that cocaine seeking increases during abstinence (incubation of cocaine craving). Recently, studies using intermittent-access self-administration showed increased motivation to self-administer and seek cocaine. We examined whether intermittent cocaine self-administration would potentiate incubation of craving in male and female rats and examined the estrous cycle's role in this incubation. METHODS: In experiment 1, male and female rats self-administered cocaine either continuously (8 hours/day) or intermittently (5 minutes ON, 25 minutes OFF × 16) for 12 days, followed by relapse tests after 2 or 29 days. In experiments 2 and 3, female rats self-administered cocaine intermittently for six, 12, or 18 sessions. In experiment 4, female rats self-administered cocaine continuously followed by relapse tests after 2 or 29 days. In experiments 3 and 4, the estrous cycle was measured using a vaginal smear test. RESULTS: Incubation of cocaine craving was observed in both sexes after either intermittent or continuous drug self-administration. Independent of access condition and abstinence day, cocaine seeking was higher in female rats than in male rats. In both sexes, cocaine seeking on both abstinence days was higher after intermittent drug access than after continuous drug access. In female rats, incubation of craving after either intermittent or continuous drug access was significantly higher during estrus than during non-estrus; for intermittent drug access, this effect was independent of the training duration. CONCLUSIONS: In both sexes, intermittent cocaine access caused time-independent increases in drug seeking during abstinence. In female rats, the time-dependent increase in drug seeking (incubation) is critically dependent on the estrous cycle phase.