Blocking of acquisition but not expression of conditioned fear-potentiated startle by NMDA antagonists in the amygdala

Receptors for N-methyl-D-aspartate (NMDA) seem to have a critical role in synaptic plasticity. NMDA antagonists (such as AP5) prevent induction of long-term potentiation, an activity-dependent enhancement of synaptic efficacy mediated by neural mechanisms that might also underlie learning and memory. They also attenuate memory formation in several behavioural tasks; there are few data, however, implicating an NMDA-sensitive measure of conditioning based on local infusion of antagonists into a brain area tightly coupled to the behavioural response used to assess conditioning. We now show that NMDA antagonists infused into the amygdala block the acquisition, but not the expression, of fear conditioning measured with a behavioural assay mediated by a defined neural circuit (fear-potentiation of the acoustic startle reflex). This effect showed anatomical and pharmacological specificity, and was not attributable to reduced salience of the stimuli of light or shock used in training. The data indicate that an NMDA-dependent process in the amygdala subserves associative fear conditioning.     

At least two genes reside within a large intron of the dunce gene of Drosophila

The dunce locus of Drosophila melanogaster is considered to house a gene involved in memory, because flies carrying lesions at the locus have shortened memory of several different conditioned behaviours. Our recent partial characterization of the gene at the molecular level, along with prior genetic and biochemical evidence, recently provides compelling evidence that the gene codes for the enzyme cAMP phosphodiesterase. The observation that the gene encodes at least six overlapping poly(A)+ RNA molecules ranging in size from 4.2 to 9.5 kilobases (kb) (ref. 8), suggests that the gene is extraordinarily complex. Here we provide the sequence of a dunce complementary DNA clone and the corresponding genomic coding regions which show that the organization of the gene is elaborate. The cDNA clone defines dunce exons which are separated by a large intron of 79 kb. More importantly, at least two other genes are shown to reside within the large intron, including the well-defined glue protein gene, Sgs-4. The location of dunce exons relative to the molecular breakpoints of chromosomal aberrations with defined cytological positions indicates that the dunce gene extends over more than five polytene chromosome bands.     

A new T-cell receptor gene located within the alpha locus and expressed early in T-cell differentiation

A new T-cell receptor gene lies just 5' to the J alpha C alpha coding regions. Its placement in this location suggests a novel mechanism for the regulation of expression of one T-cell receptor polypeptide to another during ontogeny. Rearrangement of this locus occurs very early in thymic differentiation and its RNA expression parallels that of the gamma-chain in thymic subpopulations, making this a possible candidate for the recently described delta-chain of the T-cell receptor.     

Uterine fluid from progesterone treated rabbits contains subcellular membranes

Summary Uterine fluid from progesterone treated rabbits was shown to be rich in subcellular membrane components consisting of vesicles and cilia-like fragments. In contrast, uterine fluid from untreated does lacked subcellular membranes. Thus, they arise when uterine sperm capacitation ability is suppressed.The assistance of Mr R. Byrne is gratefully acknowledged. Mr K. Bedigian skilfully prepared the electron micrographs. Financial support was received from N.I.H. grant HD 10206-01.