There is no understanding of the role of cholesterol and phospholipids in the mechanisms of synaptic function and neurodegeneration. Here we report that cholesterol disbalance is critical for synaptic transmission and plasticity as investigated by a study of paired pulse facilitation (PPF) and long‐term potentiation (LTP). Extracellular recording of field‐evoked postsynaptic potentials showed enhanced PPF ratio and an impairment of LTP in CA1 subfield of adult rat ex‐vivo hippocampal slices subjected to cyclodextrin‐ or normal human CSF‐HDL3‐mediated cholesterol efflux. Immunofluorescence with antibodies against neurofilament and tau revealed that cholesterol and phospholipids depletion causes alteration of normal hippocampal neurites and the appearance of PHF‐tau in the mossy fibers. We further find that LTP and amyloid β protein increase [14C]acetate label incorporation into newly synthesized hippocampal membrane lipids. Our results indicate the importance of neuronal cholesterol redistribution and synthesis for synaptic plasticity and neurodegeneration.

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Transcription of eukaryotic protein-encoding genes by RNA polymerase II is modulated by two distinct classes of transcription factors. The first class comprises general transcription factors which are necessary for accurate initiation of transcription. These factors include TFIIA, TFIIB, TFIID, TFIIE, TFIIF, TFIIG/J, and TFIIH (11, 82). TFIID is a multiprotein complex consisting of TATA-binding protein (TBP) complexed with a number of TBP-associated factors (73). The binding of TFIID is thought to be the first step in transcriptional initiation (11, 82). The subsequent binding of TFIIB is thought to be involved in bringing RNA polymerase II to the complex through the association of TFIIF (34, 37). This leads to the recruitment of TFIIE and TFIIH and possibly other factors, which ultimately results in the initiation of transcription (11,75,82).The magnitude of transcriptional activity is greatly affected by the second class of transcription factors that generally bind to distal control DNA elements (52). These sequence-specific factors act to either promote or inhibit the formation of an active transcriptional initiation complex. Recent in vitro transcription studies suggest that the entry of TFIIB may be rate limiting for transcriptional initiation and that several transcriptional activators act to recruit or stabilize the interaction of TFIIB with the initiation complex (14, 62). TFIIB contains a potential N-terminal zinc finger structure (amino acids 14 to 36) that may be important for interaction with RNA polymerase II and TFIIF (34), a more C-terminal amphipathic ␣ helix (amino acids 184 to 201), and two imperfect repeats (amino acids 124 to 201 and 218 to 294) (34,37,62) (Fig. 1A). The amphipathic ␣ helix appears to be important for interaction with TBP (34, 37) and several transcriptional activators such as the herpes simplex virus VP16 protein (62).Members of the steroid/thyroid hormone receptor gene family are sequence-specific DNA-binding proteins that play important roles in gene regulation. The steroid hormone receptor subfamily includes the receptors which mediate the effects of glucocorticoids, progestins, mineralocorticoids, androgens, and estrogens (12, 16). The thyroid/retinoid receptor subfamily (16, 21) includes receptors that mediate the effects of thyroid hormone (3,5,3Ј-triiodo-L-thyronine [T3]), all-trans retinoic acid, 9-cis retinoic acid, and 1,25-dihydroxyvitamin D 3 as well as several orphan receptors (e.g., COUP-TF and c-ErbA␣2) whose ligands, if any, are unknown (26,27,44). Steroid/thyroid receptors bind to specific DNA sequences known as hormone response elements (HREs) and mediate ligand-dependent ac-

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