j *@ - Sociedade Brasileira de Psicologia

142
only in its initial stages, has. yet to be resumed; however I shal describe the results
that were obtained and discuss them in relation to previous work and to comparative
data from other insect species.
RESULTS
As it is not possible in the bee to penetrate the basement membrane with
micropipettes as in the fly, access was made to the lam ina through a small window
cut in the head capsule just above the cùrnea and the electrode driven roughly
verticatly downwards. In some cases it was apparent from the abrupt changes in position
of the light-sensitive onzmatidia, that cels were being penetrated in the chiasma
rather than in the lamina. Whenever possible two or even three cells were recorded
from and injected in the same animal, care being taken to advance the electrode at
least 100 u between cels. Nevertheless sometimes fewer and sometimes more cells
were marked than injected, leaving some doubt as to the corect correspondence.
This may have been dpe to slight leakage from the electrode during permanence in or
passage through cels not injected or by leakage of dye from an injected cel into a
neighbouring one which had been pierced by the electrode .
'
A Xenon .lamp in conjuntion with a monochromator and a variable density
neutral filter, both controled by a gomputer, provided a point light source. The most
frequent response form to a 1 sec ççsquare'' light stimulus of near saturating intensity,
adjusted to the axis of the light-sensitive ommatidium, had a hyperpolarizing phasic
peak, folowed by a sustained or gradually decaying plateau and a smaller phasic
depolarizing peak at light off . Some cells displayed rising rather than decaying plateaux
which, in at least one case, reached a gréater potential than the peak. Other' cels had
little or no plateau and some had no peak before the plateau. One cel responded 'with
a phasic depolarization under green and bll!e light and a sustained depolarization in the
UV; another short-lived unmarked cel responded with a rising depolarization in green
and blue and a phasic hyperpolarization in the UV. Tltree cels started spiking after
s'ome delay' after penetratiön; two of these spiked at light OFF and the other during
light ON. Recently I was able to confirm spiking responses irl some pilot tests in the
lamina' of the tropical bee Melipona t/zldrl:fklcflfl. As previously reported by Menzel
(1974) low frequency noise is greter than in retinular cels in the dark, and increases
under low to medium illumination. . .
Peak response/intensity (v/log 1) functions are much steeper than for phptoreceptors:
the most frequent s values for the Lipetz equation (150/1 ='(Vsat/Vm-1)1/s,
where Vsat is estimated saturation peak amplitude, 150. is the stimulus intensity
coresponding to Vm/vsat = 50% and s is a measure of the inclination of the sigmoid,
Solza and Ventura, 1989) were 1,7 as compared to 0,7 for photoreccptors. This
coresponds to a contrast eficiency (defined by Menzel (1974) as percentage increase