Alan J. Pollack

An implantable biofuel cell for a live insect.

A biofuel cell incorporating a bienzymatic trehalase|glucose oxidase trehalose anode and a bilirubin oxidase dioxygen cathode using Os complexes grafted to a polymeric backbone as electron relays was designed and constructed. The specific power densities of the biofuel cell implanted in a female Blaberus discoidalis through incisions into its abdomen yielded maximum values of ca. 55 μW/cm(2) at 0.2 V that decreased by only ca. 5% after ca. 2.5 h of operation.

Control of obstacle climbing in the cockroach, Blaberus discoidalis. I. Kinematics

Abstract. An advantage of legged locomotion is the ability to climb over obstacles. We studied deathhead cockroaches as they climbed over plastic blocks in order to characterize the leg movements associated with climbing. Movements were recorded as animals surmounted 5.5-mm or 11-mm obstacles. The smaller obstacles were scaled with little change in running movements. The higher obstacles required altered gaits, leg positions and body posture. The most frequent sequence used was to first tilt the front of the body upward in a rearing stage, and then elevate the center of mass to the level of the top of the block. A horizontal running posture was re-assumed in a leveling-off stage. The action of the middle legs was redirected by rotations of the leg at the thoracal-coxal and the trochanteral-femoral joints. The subsequent extension movements of the coxal-trochanteral and femoral-tibial joints were within the range seen during horizontal running. The structure of proximal leg joints allows for flexibility in leg use by generating subtle, but effective changes in the direction of leg movement. This architecture, along with the resulting re-direction of movements, provides a range of strategies for both animals and walking machines.

Neural Activity in the Central Complex of the Insect Brain Is Linked to Locomotor Changes

Animals negotiating complex natural terrain must consider cues around them and alter movement parameters accordingly. In the arthropod brain, the central complex (CC) receives bilateral sensory relays and sits immediately upstream of premotor areas, suggesting that it may be involved in the context-dependent control of behavior. In previous studies, CC neurons in various insects responded to visual, chemical, and mechanical stimuli, and genetic or physical lesions affected locomotor behaviors. Additionally, electrical stimulation of the CC led to malformed chirping movements by crickets, and pharmacological stimulation evoked stridulation in grasshoppers, but no more precise relationship has been documented between neural activity in the CC and movements in a behaving animal. We performed tetrode recordings from the CC of cockroaches walking in place on a slippery surface. Neural activity in the CC was strongly correlated with, and in some cases predictive of, stepping frequency. Electrical stimulation of these areas also evoked or modified walking. Many of the same neural units responded to tactile antennal stimulation while the animal was standing still but became unresponsive during walking. Therefore, these CC units are unlikely to be reporting only sensory signals, but their activity may be directing changes in locomotion based on sensory inputs.

Identification of thoracic interneurons that mediate giant interneuron-to-motor pathways in the cockroach.

Summary1.Paired intracellular recordings were made to identify thoracic interneurons that receive stable short latency excitation from giant interneurons (GIs).2.Eight metathoracic interneurons were identified in which EPSPs were correlated with GI activity which was evoked either by wind or intracellular electrical stimulation or occurred spontaneously. In all cases EPSPs in the thoracic interneurons followed GI action potentials faithfully at short latencies.3.EPSPs associated with GI action potentials consistently represented the upper range of amplitudes of a large sample of EPSPs recorded in the thoracic interneurons.4.Seven of the interneurons were correlated with activity in ventral GIs but were not correlated with activity in dorsal GIs. Four of these interneurons were part of a discrete population of interneurons whose somata are located in the dorsal posterior region of the ganglion. The eighth interneuron (designated the T cell) was positively correlated with activity in dorsal GIs.5.The four dorsal posterior group interneurons and the T cell were depolarized intracellularly to establish their potential for generating motor activity. In all cases evoked activity was stronger in leg motor neurons (primarily Ds and the common inhibitor) located on the side contralateral to the interneurons soma.6.The results indicate that significant polysynaptic pathways exist by which GI activity can evoke motor activity. The implications of this conclusion to investigations on the cockroach escape system are discussed.

Multi-unit recording of antennal mechano-sensitive units in the central complex of the cockroach, Blaberus discoidalis

The central complex (CC) is a group of midline neuropils in the protocerebrum of all insects (Williams, J Zool, 176:67–86, 1975; Strausfeld, Prog Brain Res, 123:273–284, 1999). Its columnar organization coupled with the anatomical tracts to and from this region suggests that the CC may supervise various forms of locomotion. In cockroach, lesions of the CC affect turning and controlled climbing over blocks (Ridgel et al., J Comp Physiol A, 193:385–402, 2007). Since these behaviors are largely directed by tactile cues detected by antennae, we predicted that some neurons in the CC respond to mechanical antennal stimulation. We used 16-channel probes to record from broad regions within the CC, while mechanically stimulating one or the other antenna. Using cluster cutting procedures, we examined 277 units in 31 preparations. Many of these units responded to mechanical stimulation of the antennae, and of these, most responded equally well to medial or lateral stimulation of either antenna. However, several units either responded to only one antenna or responded significantly more strongly to one of them. Most of the units responding to antennal stimulation were sensitive to changes in the velocity as well as changes in light. Our data reveal a large population of mult-sensory neurons in the CC that could contribute to locomotion control.

Control of climbing behavior in the cockroach, Blaberus discoidalis. II. Motor activities associated with joint movement

Abstract. Deathhead cockroaches employ characteristic postural strategies for surmounting barriers. These include rotation of middle legs to re-direct leg extension and drive the animal upward. However, during climbing the excursions of the joints that play major roles in leg extension are not significantly altered from those seen during running movements. To determine if the motor activity associated with these actions is also unchanged, we examined the electromyogram activity produced by the slow trochanteral extensor and slow tibial extensor motor neurons as deathhead cockroaches climbed over obstacles of two different heights. As they climbed, activity in the slow trochanteral extensor produced a lower extension velocity of the coxal-trochanteral joint than the same frequency of slow trochanteral extensor activity produces during horizontal running. Moreover, the pattern of activity within specific leg cycles was altered. During running, the slow trochanteral extensor generates a high-frequency burst prior to foot set-down. This activity declines through the remainder of the stance phase. During climbing, motor neuron frequency no longer decreased after foot set-down, suggesting that reflex adjustments were made. This conclusion was further supported by the observation that front leg amputees generated even stronger slow trochanteral extensor activity in the middle leg during climbing movements.

Motor responses to paired stimulation of giant interneurons in the cockroachPeriplaneta americana

Summary1.Dorsal giant interneurons (GIs) of the cockroach were stimulated intracellularly alone and in pairs, while activity in levator and depressor motor neurons of one metathoracic leg was recorded extracellularly.2.Paired stimulation of GI-6 (which excites primarily levators) and ipsilateral GI-7 (which excites both levators and depressors) resulted in a stronger levator response than that recorded when either GI was stimulated alone (Figs. 3, 4).3.Paired stimulation of GI-5 (which excites primarily depressors) and ipsilateral GI-7 resulted in a stronger depressor response than that recorded when either GI was stimulated alone (Fig. 7).4.Paired stimulation of GI-5 exciting depressors and ipsilateral GI-6 exciting levators resulted in increased activity in either levators or depressors, depending on the individual animal. The muscle group whose activity increased was constant in any given preparation but varied from animal to animal (Fig. 9).5.Delayed stimulation of one GI in paired trials uncovered no inhibition during the first part of the GI stimulus train (Fig. 10).6.Contralateral dorsal GIs and non-giant interneurons can also sum with dorsal GIs to elicit stronger motor outputs (Fig. 11).

Flight activity mediated by intracellular stimulation of dorsal giant interneurons of the cockroachPeriplaneta americana

Summary1.Flight activity can be initiated in legless cockroaches by stimulating a single dorsal giant interneuron (dGI) intracellularly with a train of current pulses. Ventral giant interneurons (vGIs) do not initiate flight activity.2.The initial directional responses in leg motor neurons which are characteristic of running are still evoked prior to flight initiation.3.For short flights the number of bursts in wing muscles (flight bursts) increases as the number of action potentials in the dGI is increased.4.Paired stimulation of dGIs evokes longer flight sequences. Moreover, a subthreshold train of action potentials in a single dGI can evoke flight if the train arrives within 500 ms of a previous flight.5.In flight motor neurons (FMNs), an initial depolarization precedes rhythmic oscillations that are associated with flight bursts. The timing of dGI activity is appropriate for eliciting the initial depolarization as well as the rhythmic oscillations. Stimulation of single dGIs with trains of current pulses evokes both phases of the FMN response, probably via polysynaptic pathways.6.Activity in the intracellularly stimulated dGI need not reach the mesothoracic ganglion directly in order to evoke coordinated flight activity in both the meso- and metathoracic ganglia.

Convergence of multi-modal sensory signals at thoracic interneurons of the escape system of the cockroach, Periplaneta americana

Research on the escape system of the cockroach has focused upon the role of giant interneurons in conveying information on wind stimulation from the cerci located on the abdomen to motor control centers in the thoracic ganglia. In the thoracic ganglia the ventral giant interneurons connect to a population of interganglionic interneurons referred to as type A thoracic interneurons. In this paper we have tested the type A interneurons for additional sensory inputs in the absence of ventral giant interneuron activity. We find that the cells that receive ventral giant interneuron activity are also influenced by a variety of additional sensory inputs; wind mediated activity in a pathway that descends from the head, tactile inputs from several loci, auditory stimuli and light responses. Moreover, behavioral observations indicate that at least some of these activities can alter the escape movements. The results suggest that these interneurons serve as a site of convergence for numerous types of sensory activity. They further suggest that the escape system is capable of responding to directional wind information encoded in the ventral giant interneurons in the context of a wealth of additional information.

A miniature hybrid robot propelled by legs

Describes the development of an autonomous hybrid micro-robot that uses legs for propulsion and support of the rear half of the body and uses a pair of wheels for support of the front half. McKibben artificial muscles actuate the legs and the compressed air that activates the actuators is generated by an on-board power plant comprising a pair of lithium batteries powering a gear motor driven air compressor. The control is also onboard in the form of a PIC that controls the actuators through four three-way valves that each consists of a pair of MEMS devices.