Temporally patterned activity recorded from mandibular nerves of the isolated subesophageal ganglion of Manduca.

We recorded bursts of motor neuron activity from closer and opener mandibular nerves of isolated subesophageal ganglia (SOG) and compared them with the feeding motor pattern of intact Manduca larvae. Closer bursts recorded from isolated SOG lasted from 1 to 4s, interburst interval durations lasted from 2 to 49s, and within- and between-animal variability was great. In contrast, motor activity bursts (EMGs) measured from mandibular closer muscles of intact, feeding animals lasted 0.08 to 0.24s with interburst intervals of 0.26 to 0.57s. Variability both within and between animals was small. Bath application of 10(-4)M octopamine to the isolated SOG tended to increase frequency and reduce the duration of bursts, so that they became more like those recorded during feeding.

Removing antennae and maxillae has little effect on feeding on normal host plants by two species of caterpillar.

Models of feeding regulation postulate that chemosensory information from available food both initiates and maintains feeding. However, we find that removing antennae and maxillae (AM) from Manduca sexta and Diacrisia virginica larvae has little effect on amounts eaten, patterns of feeding, and the microstructure (each bite and pause) of feeding, as quickly as two days after the operation. However, there was a small change in the microstructure of feeding of AM D. virginica. Bite frequency of AM D. virginica was significantly lower than for controls when larvae began meals without exploring the food first. Exploring was also followed by longer chewing bouts. Acute effects of the ablation were tested using only Manduca. Six hours after the operation larvae ate less than most controls by eating fewer meals and by biting more slowly. Unilateral ablates also ate less 6h post-operatively, by eating fewer meals; their bite frequency was not low. These observations suggest that chemosensory input affects bite frequency but not other aspects of feeding. As quickly as 24h post-operatively other sensory input to the CNS of AM larvae may compensate for the reduction in chemosensory information, but overall, chemosensory input appears relatively unimportant in non-choice situations.

Comparison of defolliculated oocytes and intact follicles of the cockroach using the vibrating probe to record steady currents.

Follicle cells were removed by dissection from early vitellogenic oocytes of the cockroach Blattella germanica. The vibrating probe was used to record steady currents from 19 defolliculated oocytes and 19 intact follicles of the same developmental stage. Defolliculated oocytes generated currents that were stable and distinguishable (by intensity or selective direction) from background reference values. Distributions of the intensities of reference values and experimental values were, in general, similar in both intact and defolliculated preparations. The patterns of currents generated by preparations recorded in the mid-sagittal plane were analyzed for both defolliculated oocytes (n = 8) and intact follicles (n = 10). The larger, generally more mature preparations in both groups generated patterns of current similar to the pattern seen in mid-vitellogenic follicles (focused inward near the germinal vesicle (GV), the presumptive ventral side, and broadly outward on the apo-GV side, the presumptive dorsal side). Smaller sized preparations in both groups showed inward or outward current on the apo-GV aspect and, typically, inward current at the GV. Only two defolliculated oocytes, and no intact follicles, appeared to generate outward current at the GV, and we believe this observation resulted from recording slightly outside the mid-sagittal plane. We conclude that preparations during early-vitellogenesis initially generate currents without an asymmetric pattern and that the inward flux at the GV is the first step in developing patterns of currents. The results suggest that the oocyte (and not the follicle cell epithelium) is responsible for generating the various patterns of currents observed in early-vitellogenic stages. At the end of early-vitellogenesis, the follicle cell epithelium begins to adhere tightly to the oocyte. The possibility is considered that the follicle cells may influence the currents generated during mid-vitellogenesis.

Behavior as a window on physiology: a simple apparatus for recording caterpillar feeding.

Regulation of feeding is a fundamental element of homeostasis. This is reflected in the similarity of control mechanisms in a wide range of animals, including insects and humans. A close examination of feeding behavior can illuminate the physiological processes driving regulation. A simple, inexpensive method for recording fine details of feeding by caterpillars is described. Possible experiments, interpretation of the data, and the relationship of observations to the underlying physiology, are outlined.

Patterns of ionic currents around the developing oocyte of the German cockroach, Blattella germanica.

The development of patterns of current around vitellogenic oocytes of the cockroach, Blattella germanica, was examined by means of a two-dimensional vibrating probe. Previtellogenic oocytes exhibited small unstable currents. Shortly after vitellogenic uptake began (oocytes 0.6-0.8 mm anterior to posterior) currents were either all inward or all outward at the plane of measurement. A dorsoventral pattern of currents was first observed around oocytes a little larger than 0.8 mm. Current exited dorsally (source) and entered ventrally (sink). In these oocytes source and sink were small, less than half the anterior-posterior length. As oocytes grew, relative sizes of source and sink increased until they extended across the major part of dorsal and ventral surfaces. Many late vitellogenic oocytes had a pattern of dorsal outward current with a bimodal distribution. At the onset of chorionation measured currents were again small, unstable, and exhibited no well-defined pattern. Current density was greatest during midvitellogenesis.

Modeling Currents About Vitellogenic Oocytes of the Cockroach, Blattella germanica.

An insect oocyte with a disc-shaped sink of current on its ventral surface during a vitellogenic phase of development is used to demonstrate modeling of expected currents arising from a mathematically defined source. A simple model with an analytical solution for the expected currents is compared to a more complex model in which expectations are computed by mathematical integration. The currents about two oocytes of different pattern type are interpreted in light of the two models.