Late-associativity, synaptic tagging, and the role of dopamine during LTP and LTD

Protein synthesis-dependent, synapse input-specific late phases of long-term potentiation (LTP) and depression (LTD) may underlie memory formation at the cellular level. Recently, it was described that the induction of LTP can mark a specifically activated synapse by a synaptic tag to capture synapse non-specific plasticity-related proteins (PRPs) and thus maintaining input-specific LTP for prolonged periods. Here we show in rat hippocampal slices in vitro, that the induction of protein synthesis-dependent late-LTD is also characterized by synaptic tagging and that heterosynaptic induction of either LTD or LTP on two sets of independent synaptic inputs S1 and S2 can lead to late-associative interactions: early-LTD in S2 was transformed into a late-LTD, if late-LTP was induced in S1. The synthesis of process-independent PRPs by late-LTP in S1 was sufficient to transform early- into late-LTD in S2 when process-specific synaptic tags were set. We name this new associative property of cellular information processing 'cross-tagging.'     

The interaction of oculomotor cues and stimulus size in stereoscopic death constancy.

In the natural world, observers perceive an object to have a relatively fixed size and depth over a wide range of distances. Retinal image size and binocular disparity are to some extent scaled with distance to give observers a measure of size constancy. The angle of convergence of the two eyes and their accommodative states are one source of scaling information, but even at close range this must be supplemented by other cues. We have investigated how angular size and oculomotor state interact in the perception of size and depth at different distances. Computer-generated images of planar and stereoscopically simulated 3-D surfaces covered with an irregular blobby texture were viewed on a computer monitor. The monitor rested on a movable sled running on rails within a darkened tunnel. An observer looking into the tunnel could see nothing but the simulated surface so that oculomotor signals provided the major potential cues to the distance of the image. Observers estimated the height of the surface, their distance from it, or the stereoscopically simulated depth within it over viewing distances which ranged from 45 cm to 130 cm. The angular width of the images lay between 2 deg and 10 deg. Estimates of the magnitude of a constant simulated depth dropped with increasing viewing distance when surfaces were of constant angular size. But with surfaces of constant physical size, estimates were more nearly independent of viewing distance. At any one distance, depths appeared to be greater, the smaller the angular size of the image. With most observers, the influence of angular size on perceived depth grew with increasing viewing distance. These findings suggest that there are two components to scaling. One is independent of angular size and related to viewing distance. The second component is related to angular size, and the weighting accorded to it grows with viewing distance. Control experiments indicate that in the tunnel, oculomotor state provides the principal cue to viewing distance. Thus, the contribution of oculomotor signals to depth scaling is gradually supplanted by other cues as viewing distance grows. Binocular estimates of the heights and distances of planar surfaces of different sizes revealed that angular size and viewing distance interact in a similar way to determine perceived size and perceived distance.     

Massed and spaced learning in honeybees: the role of CS, US, the intertrial interval, and the test interval

Conditioning the proboscis extension reflex of harnessed honeybees (Apis mellifera) is used to study the effect temporal spacing between successive conditioning trials has on memory. Retention is monitored at two long-term intervals corresponding to early (1 and 2 d after conditioning) and late long-term memory (3 and 4 d). The acquisition level is varied by using different conditioned stimuli (odors, mechanical stimulation, and temperature increase at the antenna), varying strengths of the unconditioned stimulus (sucrose), and various numbers of conditioning trials. How learning trials are spaced is the dominant factor both for acquisition and retention, and although longer intertrial intervals lead to better acquisition and higher retention, the level of acquisition per se does not determine the spacing effect on retention. Rather, spaced conditioning leads to higher memory consolidation both during acquisition and later, between the early and long-term memory phases. These consolidation processes can be selectively inhibited by blocking protein synthesis during acquisition.     

Trends in attempted suicide in Denmark, 1976-1980

The object of the present study was to estimate proportions and changes in the incidence of suicide attempts in Denmark. Case sheets concerning all admissions in 1976-1979 (total 6,650) at the Department of Psychiatry, Odense University Hospital (the catchment area of which provides a representative sample of the Danish population), were examined with a view to establishing the reasons for admission. Rates of suicide attempts by age and sex in 1976-1979 were calculated, and estimated rates of the suicide attempts in 1980 added. Trend analysis showed an increase in the mean rates from 1976 to 1979 of 48%, followed by a decrease in 1980 of 13%. There were high increases among the adolescents, but the increase was above all due to the fact that more and more men attempted suicide; the study suggests as a new phenomenon more male than female suicide attempters. We stress the fact that incidences calculated on the basis of hospital admissions only underestimate the real proportions of self-destructive behavior.