The visual pigments of all invertebrates investigated so far are membrane-coupled chromoproteids having similar spectral absorption characteristics, the chromophore of which has been, in certain species, shown to be the same as that of the vertebrate rhodopsin (11-cis-retinal). In this study rhodopsin is symbolized by P and its photoproduct metarhodopsin by M, and where wavelengths of maximal absorption (λmax) for these are known, then this is also denoted, e.g., P490, or M580.

The Physiology of Invertebrate Visual Pigments

Animals use vision to perform such diverse behaviors as finding food, interacting socially with other animals, choosing a mate, and avoiding predators These behaviors are complex and the visual system must process color, motion, and pattern cues efficiently so that animals can respond to relevant stimuli The visual system achieves this by dividing visual information into separate pathways, but to what extent are these parallel streams separated in the brain? To answer this question, we recorded intracellularly in vivo from 105 morphologically identified neurons in the lobula, a major visual processing structure of bumblebees (Bombus impatiens) We found that these cells have anatomically segregated dendritic inputs confined to one or two of six lobula layers Lobula neurons exhibit physiological characteristics common to their respective input layer Cells with arborizations in layers 1–4 are generally indifferent to color but sensitive to motion, whereas layer 5–6 neurons often respond to both color and motion cues Furthermore, the temporal characteristics of these responses differ systematically with dendritic branching pattern Some layers are more temporally precise, whereas others are less precise but more reliable across trials Because different layers send projections to different regions of the central brain, we hypothesize that the anatomical layers of the lobula are the structural basis for the segregation of visual information into color, motion, and stimulus timing

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The Processing of Color, Motion, and Stimulus Timing Are Anatomically Segregated in the Bumblebee Brain

Visual scenes comprise enormous amounts of information from which nervous systems extract behaviorally relevant cues. In most model systems, little is known about the transformation of visual information as it occurs along visual pathways. We examined how visual information is transformed physiologically as it is communicated from the eye to higher-order brain centers using bumblebees, which are known for their visual capabilities. We recorded intracellularly in vivo from 30 neurons in the central bumblebee brain (the lateral protocerebrum) and compared these neurons to 132 neurons from more distal areas along the visual pathway, namely the medulla and the lobula. In these three brain regions (medulla, lobula, and central brain), we examined correlations between the neurons' branching patterns and their responses primarily to color, but also to motion stimuli. Visual neurons projecting to the anterior central brain were generally color sensitive, while neurons projecting to the posterior central brain were predominantly motion sensitive. The temporal response properties differed significantly between these areas, with an increase in spike time precision across trials and a decrease in average reliable spiking as visual information processing progressed from the periphery to the central brain. These data suggest that neurons along the visual pathway to the central brain not only are segregated with regard to the physical features of the stimuli (e.g., color and motion), but also differ in the way they encode stimuli, possibly to allow for efficient parallel processing to occur.

https://www.jneurosci.org/content/jneuro/29/32/9987.full.pdf

Visual processing in the central bee brain

In the honey bee drone, the decrease in sensitivity to light of a retinula cell exposed to background illumination was found to be accurately reflected by the difference in amplitude between the initial transient depolarization and the lowest steady depolarization evoked by the background light. It is shown that both the decrease in sensitivity to light and the accompanying drop in potential from the transient to the plateau can be prevented by injecting EGTA intracellularly. A decrease in duration and amplitude of responses to short test flashes such as observed immediately after illumination was found to occur too when Ca or Na, but not K, Li, or Mg injected into dark-adapted retinula cells. Injection of EGTA into a retinula cell maintained a steady state of light adaptation, was found to cause an increase in amplitude and duration of the response to a short test flash, thus producing the effects of dark adaptation. It is suggested that, in the retina of the honey bee drone, an increase in intracellular calcium concentration plays a central role in light adaptation and that an increase in intracellular sodium concentration, resulting from the influx of sodium ions during the responses to light, could lead to this increase in intracellular free calcium.

/pdf/role-of-intracellular-calcium-and-sodium-in-light-adaptation-12fqqtsf12.pdf

B. Hadjilazaro

Papers

A depolarizing aftereffect of intense light in the drone visual receptor.