Helmut V. B. Hirsch

Rearing in darkness changes visually-guided choice behavior in Drosophila

To test whether visual experience can affect development of visual behavior in the fruitfly, Drosophila, we measured the visually-guided choice behavior of groups of flies reared in complete darkness, compared with controls reared in a normal light/dark cycle. We used a simple visual preference test, i.e. choice among four different visual targets each consisting of vertical black lines of a particular width on a white background, using a blind testing procedure so that the individual rearing histories were not known by the tester. Both groups of flies were strongly attracted to the vertical lines; however, generally the dark-reared flies were more attracted to the wider stimulus lines than were the control flies. Control experiments in which normally reared adults were kept for several days in darkness showed that the effects of dark-rearing were not simply due to being in darkness, but depended upon the timing of the deprivation. The results indicate that the development of visual behavior can be affected by visual experience in Drosophila and thus open the possibility of using Drosophila for genetic dissection of mechanisms of visual plasticity.

Principal components analysis of cells in cat visual cortex

Abstract Cortical cells differ along many dimensions, and statistical techniques are needed to study the relationships among them. We have used principal components analysis to study variation within a population of cells in the visual cortex of the cat. This procedure transforms the data which may then be projected onto a small number of independent axes. The axes are hierarchically ordered in terms of the sample variance they account for so that subsequent components account for decreasing proportions of the total sample variance. Four principal components (PCs) were identified by the analysis. The contributing variables on these components were respectively: (1) cutoff velocity, peak response, receptive field area and spontaneous activity; (2) tuning width, orientation selectivity, occular dominance ratio and obliquity; (3) directionality ratio, monocularity and vvariability; and (4) width to length ratio, variability and sideband ratio. We hypothesize that each of these components identifies a physiologically important feature of cortical organization. PC 1 and PC 4 describe those relationships among variables that have been used previously by other workers to classify cells in the visual cortex of the cat. Specifically, PC 1 is highly correlated with those variables associated with type of afferent input and PC 4 is highly correlated with those variables that differentiate simple cells from complex cells. PC 2 and PC 3 , however, are highly correlated with variables that have not been used in classiying cells. Our results demonstrate that: (1) each of two major classification schemes (simple/complex and classification by afferent input) describe important differences among neurons in the cats visual cortex and both must be incorporated into a comprehensive system for classifying cells in the cats visual cortex; and (2) these two schemes when combined do not account for all the major differences among neurons in cat visual cortex, and at least two additional components are required: one related to orientation selectivity and dominance by the ipsilateral eye, and another related to directional selectivity and the degree of binocular interaction.

Accumulation, elimination, sequestration, and genetic variation of lead (Pb2+) loads within and between generations of Drosophila melanogaster

We examined accumulation, sequestration, elimination, and genetic variation for lead (Pb) loads within and between generations of Drosophila melanogaster. Flies were reared in control or leaded medium at various doses and tested for their Pb loads at different stages of development (larvae, eclosion, newly-eclosed adults, and mature adults). Pb loads were tested using Inductively Coupled Plasma Mass Spectrometry (ICP-MS). We found that D.xa0melanogaster readily accumulated Pb throughout their lifespan and the levels of accumulation increased with Pb exposure in the medium. Wandering third-instar larvae accumulated more Pb than mature adults; this phenomenon may be due to elimination of Pb in the pupal cases during eclosion and/or depuration in adults post-eclosion. The accumulated Pb in mature adults was not transferred to F1 mature adult offspring. Using a set of recombinant inbred strains, we identified a quantitative trait locus for adult Pb loads and found that genetic variation accounted for 34% of the variance in Pb load. We concluded that D.xa0melanogaster is a useful model organism for evaluating changes in Pb loads during development, as well as between generations. Furthermore, we found that genetic factors can influence Pb loads; this provides an essential foundation for evaluating phenotypic variation induced by the toxic effects of Pb.

Removal of the more-experienced eye decreases visual field deficits in cats reared with unequal alternating monocular exposure

Unequal alternating monocular exposure produces a nasal field deficit for the less-experienced eye, which persists despite prolonged unrestricted binocular exposure. We now report that this deficit decreases after the more experienced eye is removed. Prior to enucleation, the visual field of the less-experienced eye was restricted to the temporal hemifield; 5 months after enucleation of the more-experienced eye, this field extended into the nasal field. Our results are consistent with those in monocularly-deprived cats, and with the occasional recovery of human amblyopes after loss of the fixating eye.

Exposure to cold: aversive Pavlovian conditioning in individual Drosophila melanogaster

Abstract. Temperature changes can be especially threatening for ectotherms, such as Drosophila melanogaster (Diptera: Drosophilidea Meigen, 1830 ), and in this study we tested whether flies can associate olfactory stimuli with a sudden drop in temperature. Such Pavlovian conditioning would allow them to make appropriate behavioural and/or physiological responses in the future. We found that exposing individual flies to one of two odours in the presence of a sudden drop in temperature resulted in Pavlovian conditioning with flies subsequently avoiding the odour paired with cold. The characteristics of Pavlovian conditioning in flies were comparable to those observed for mammalian species. Specifically, the strength of conditioning increased with increasing intensity of the cold and decreased as the time interval between the olfactory stimulus (CS) and cold (US) was lengthened. Finally, the order in which CS and US were presented affected the strength of conditioning. Learning was observed when the CS preceded US and when the US immediately preceded the CS, but not when the CS preceded the US by 30u2003s or more. These results provide further evidence for learning in individual flies, and confirm that Pavlovian conditioning is a general mechanism used by organisms to obtain information about their environment.