Biology subjects

Städele, C.

Publications and source records attributed to Städele, C..

3 recordsLinked to original sources

bioRxiv2023

The black-legged tick Ixodes scapularis detects CO2 without the Haller's organ

Both male and female ticks have a strong innate drive to find and blood-feed on hosts. Carbon dioxide (CO2) is considered a critical behavioral activator and attractant for ticks and an essential sensory cue to find hosts. Yet, how CO2 activates and promotes host-seeking in ticks is poorly understood. We studied CO2 responses in the black-legged tick Ixodes scapularis, the primary vector for Lyme disease in North America. Adult males and females were exposed to 1, 2, 4, or 8% CO2, and changes in walking behavior and foreleg movement were analyzed. We find that CO2 is a potent stimulant for adult Ixodes scapularis, even at lower concentrations (1%). Behavioral reactions depend on the animals state: Walking ticks increase their walking speed, while stationary ticks start to wave their forelegs and begin to quest - both behaviors resembling aspects of host-seeking. Furthermore, Ixodes scapularis has no clear concentration preference and is not tuned more robust to breath-like CO2 concentrations ([~]4%) than to the other concentrations tested. As soon as the CO2 level is above a certain threshold, Ixodes scapularis react, indicating that CO2 acts as a behavioral activator and can be used as a long-distance cue to detect approaching hosts. Moreover, we provide convincing evidence that the foreleg Hallers organ is not necessary for CO2 detection. Even with disabled or amputated Hallers organ, Ixodes scapularis respond robustly to CO2, signifying that there must be CO2-sensitive structures important for tick host-seeking that have not yet been identified.

physiology↗

bioRxiv2021

The hyperpolarization-activated current shifts the dynamic range of a voltage-dependent electrical synapse

Like their chemical counterparts, electrical synapses show complex dynamics such as rectification and voltage dependence that interact with other electrical processes in neurons. The consequences arising from these interactions for the electrical behavior of the synapse, and the dynamics they create, remain largely unexplored. Using a voltage-dependent electrical synapse between a descending modulatory projection neuron (MCN1) and a motor neuron (LG) in the crustacean stomatogastric ganglion, we find that the influence of the hyperpolarization-activated inward current (Ih) is critical to the function of the electrical synapse. When we blocked Ih with CsCl, the apparent voltage dependence of the electrical synapse shifted by 18.7 mV to more hyperpolarized voltages, placing the dynamic range of the electrical synapse outside of the range of voltages used by the LG motor neuron (-60.2 mV - -44.9 mV). With dual electrode current- and voltage-clamp recordings, we demonstrate that this voltage shift is not due to a change in the properties of the gap junction itself, but is a result of a sustained effect of Ih on the presynaptic MCN1 axon terminal membrane potential. Ih-induced depolarization of the axon terminal membrane potential increased the electrical postsynaptic potentials and currents. With Ih present, the axon terminal resting membrane potential depolarized, shifting the dynamic range of the electrical synapse towards the functional range of the motor neuron. We thus demonstrate that the function of an electrical synapse is critically influenced by a voltage-dependent ionic current (Ih). New & NoteworthyElectrical synapses and voltage-gated ionic currents are often studied independently from one another, despite mounting evidence that their interactions can alter synaptic behavior. We show that the hyperpolarization-activated inward ionic current shifts the voltage dependence of an electrical synaptic transmission through its depolarizing effect on the membrane potential, enabling it to lie within the functional membrane potential range of a motor neuron. Thus, the electrical synapses function critically depends on the voltage-gated ionic current.

neuroscience↗

bioRxiv2021

Neuromodulation enables temperature robustness and coupling between fast and slow oscillator circuits in Cancer borealis

Acute temperature changes can disrupt neuronal activity and coordination with severe consequences for animal behavior and survival. Nonetheless, two rhythmic neuronal circuits in the crustacean stomatogastric ganglion (STG) and their coordination are maintained across a broad temperature range. However, it remains unclear how this temperature robustness is achieved. Here, we dissociate temperature effects on the rhythm generating circuits from those of upstream ganglia. We demonstrate that heat-activated factors extrinsic to the rhythm generators are essential to the slow gastric mill rhythms temperature robustness and contribute to the temperature response of the fast pyloric rhythm. The gastric mill rhythm crashed when only the STG circuits were heated. It could be restored when upstream ganglia were heated in addition, and the activity of the peptidergic modulatory projection neuron (MCN1) increased. Correspondingly, MCN1s neuropeptide transmitter stabilized the rhythm and maintained it over a broad temperature range. Extrinsic neuromodulation is thus essential for the oscillatory circuits in the STG and enables neural circuits to maintain function in temperature-compromised conditions. In contrast, integer coupling between pyloric and gastric mill rhythms was independent of whether extrinsic inputs and STG pattern generators were temperature-matched or not, demonstrating that the temperature robustness of the coupling is enabled by properties intrinsic to the rhythm generators. However, at near-crash temperature, integer coupling was maintained only in some animals but was absent in others. This was true despite regular rhythmic activity in all animals, supporting that degenerate circuit properties result in idiosyncratic responses to environmental challenges.

neuroscience↗