Pathfinding and target selection of goldfish retinal axons regenerating under TTX-induced impulse blockade.

To define the extent to which impulse blockade interferes with the morphological changes of regenerating retinal axons during their growth through the tectum, axons were deprived of activity by repeated intraocular injections of TTX. At intervals between 24 and 189 days after optic nerve section (ONS), a defined group of TTX-silenced axons and of axons with normal activity (controls) were labeled by applications of HRP to the ventro- or dorsotemporal retina. The trajectories of these labeled axons were traced in DAB processed tectal wholemounts. As in controls, TTX-blocked axons went through a phase of exploratory growth at early regeneration stages (24 to 80 days after ONS). Coursing in abnormal routes, the axons initially distributed their growing endings widely over the tectum. Axons with and without activity extended side branches with growth cones and filopodia over all regions of the tectum. These ramifications were of similar dimensions for the TTX-blocked and control axons. Despite abnormal routes and branching over inappropriate territories, axons showed a preference for the rostral tectum. At late regeneration stages (120-189 days after ONS), axons had lost their side branches and their growth cones. Their preterminal segments exhibited striking bends, suggesting that they had undergone course corrections to achieve access to the retinotopic target. Axonal processes had disappeared from the caudal tectum, and the preferential accumulation of axons over the rostral tectum had increased. The majority of the TTX-blocked and control axons ended in terminal arbors at retinotopic regions. The labeled arbors of the TTX-group were no larger than those of the control group. The arbors of each group lay close together in a continuous cluster in the TTX-group as well as in two-thirds of the control group. In the other one-third of the control group, however, terminal arbors were aggregated into separate patches. The clusters of the TTX-blocked axons covered between 2.2 and 3.9% (mean 2.95%) of the tectal surface and the clusters and/or patches of active axons between 1.9 and 3.4% (mean 2.7%). Thus the terminal arbor clusters of the TTX-silenced axons were not significantly larger than those of the active axons. These data show that retinal ganglion cell impulse activity is required for neither the extension of side branches in the early exploratory phase of regeneration nor for the withdrawal of these branches nor for the establishment of target-directed routes and the deployment of normal-size terminal arbors at retinotopic loci.(ABSTRACT TRUNCATED AT 400 WORDS)

Preferential loss of collaterals from goldfish retinal axons in the optic tract is delayed by tetrodotoxin.

Following optic nerve section (ONS) in goldfish, the right eye was repeatedly injected with tetrodotoxin (TTX) and the left eye with Ringer solution. At various survival periods after ONS, horseradish peroxidase (HRP) was applied to small groups of axons in dorsal or ventral retina in both eyes. Counts of labeled regenerating retinal axons show that 43 +/- 4.6% of regenerating axons course through the inappropriate brachium of the optic tract between 20 and 65 days after ONS. The amount of misrouted axons declines to 30 +/- 6.1% between 70 and 80 days after ONS. Under TTX blockade the reduction of misrouted axons is delayed but reaches 27 +/- 3.6% at 150 days after ONS.

Appetitive learning of odours with different behavioural meaning in moths.

Moth behaviour is to a great extent guided by olfactory stimuli with different relevance. We investigated whether olfactory learning of odours is influenced by the behavioural significance of the odorant. In proboscis extension conditioning experiments species-specific sex pheromones, which normally elicit an innate behaviour in males, and a flower odour were used as olfactory stimuli. After 10 conditioning trials, both sexes showed similar response levels to individual pheromone components and to the flower odour geraniol. However, when the female gland extract was used as conditioning stimulus, the response level was significantly lower than that for geraniol in both sexes. Significant learning nevertheless occurred in females, but not in males. Experiments with different numbers of training trials revealed that, in females, fewer learning trials with individual pheromone components were necessary for significant memory formation than in males.

Behavioral response of femaleHelicoverpa (Heliothis)armigera HB. (Lepidoptera: Noctuidae) moths to synthetic pigeonpea (Cajanus cajan L.) kairomone.

FemaleH. armigera moths are highly attracted by a steam distillate from pigeonpea plants, one of their main hosts. A mixture of six compounds, all sesquiterpenes (ß-caryophyllene,α-humulene,α-guajene,α-muurolene,γ-muurolene, andα-bulnesene), mixed in the proportions as found in the steam distillate, elicited the same behavioral responses (oriented upwind flights and contacts with the odor source) as the steam distillate. Onlyα-bulnesene was attractive by itself, but still less than the whole mixture. In addition, the sesquiterpene mixture acts as an oviposition stimulant. Both behavioral responses, orientation and oviposition, are concentration dependent. Electrophysiological recordings from female and male antennae (EAG) showed the same qualitative and quantitative responses to each of the compounds of the sesquiterpene mixture. The EAG responses to the original steam distillate were higher and similar to chickpea kairomonal components, which were also tested. The pigeonpea sesquiterpene mixture and its individual components elicited weak EAG responses only. The response of the male antenna to female-produced pheromone components was in the same range as the pigeonpea steam distillate.