SAQ!

Describe an example of how C. elegans uses orthokinesis to explore its environment.

Orthokinesis – a change in speed C.elegans slows down when encountering food – a bacterial lawn.

Dopamine from CEP neurons and serotonin from ADF neurons control this speed change. These sensory neurons act extrasynaptically on their motor neurons. CEP sensory neurons detect food and release dopamine which binds to receptors on motor neurons, causing the warm to slow down. Additionally neurons such as ADF which detects odour and NSM which detects food ingestion contribute to food slowing by releasing serotonin which acts of MOD-1 receptors. Both serotonin and dopamine act via wireless signalling. This allows them explore their environment and remain in food rich areas.

Describe an example of how C. elegans uses klinokinesis to explore its environment.

Klinokinesis – frequency of turns C.elegens tuns frequency is based on salt concentration.

ASEL promotes forward runs and fewer turns when salt concentration is increased, and ASER promotes more turns limiting longer runs when salt concentration decreases. Additionally interneurons AIA + AIY promote forward runs and AIB + AIZ promote turns. Therefore they explore there environment by adjusting the probability of turns based on local salt concentration, with ASE sensory neurons detecting salt gradients and interneurons controlling the motor output.

Describe an example of how C. elegans uses klinotaxis to explore its environment.

Klinotaxis – head swings due to environmental stimuli
A well studied example includes the weathervane model.

They steer directionally by sensing differences in stimuli using head swings. This could be via odour gradients using AWC sensory neurons, in which the worm steers towards the side with the greater concentration. The RIA interneuron encodes the head bend direction to coordinate steering. Furthermore, the AIY interneuron receives input from AWC neuron and promotes forward runs and directional turning. Thus through the activity of the sensory neuron AWC and the interneurons RIA and AIY C.elegans use klinotaxis to steer toward favourable environmental conditions.

Give 2 examples of the specific role of interneurons in C. elegans navigation behaviour (can be orthokinesis, klinokinesis, and/or klinotaxis).

Klinokinesis involves changes in turning frequency depending on stimulus intensity. In C. elegans, the interneurons AIA and AIY promote forward runs during favourable conditions, while AIB and AIZ promote more frequent turning during unfavourable conditions, allowing the worm to explore and escape suboptimal environments.

Klinotaxis involves gradual steering by comparing stimulus changes during head swings. The interneuron AIY contributes to both forward movement and the coordination of head-directed turns. RIA integrates sensory and motor inputs to bias head bending direction, allowing the worm to steer toward or away from gradients during navigation.

Give 2 examples of the specific role of sensory neurons in C. elegans navigation behaviour (can be orthokinesis, klinokinesis, and/or klinotaxis).

Orthokinesis is when the worm changes its speed in response to stimulus intensity. It uses the sensory neuron CEP which detects the presence of food. CEP responds by releasing dopamine which causes the worm to slow down when encountering food.

Kilokinesis is when they adjust there frequency of turns based on changes in stimulus concentration and uses the sensory neurons ASEL and ASER which detect salt gradients. ASEL is the On cell which responds to increases in sodium concentration and promotes forward movement while ASER is the off cell and responds to decreases in chloride concentration promoting turning.

Describe a specific application of optogenetics in controlling neuronal activity, including the type of opsin used, the targeted neuron population, and the resulting physiological effect.

A specific application of optogenetics was used to study the enteric nervous system in mice by expressing the light-sensitive ion channel Channelrhodopsin-2 (ChR2) in calretinin-positive excitatory neurons. Upon exposure to blue light, ChR2 opens, leading to depolarisation of these neurons. This activation triggered colonic motor complexes, which are rhythmic contractions responsible for gut motility.

Explain the importance of the blood-brain barrier and describe one strategy used to circumvent the blood-brain barrier to deliver therapeutics into the brain.

The blood-brain barrier is an important semi-permeable barrier that prevents harmful or toxic substances from travelling into the brain and into the bloodstream. It is formed by tight junctions between endothelial cells, which restrict the flow of unwanted ions and molecules. A strategy used to circumvent the bbb is through direct intracerebral injection, which allows for therapeutic agents to be delivered directly into brain tissue, bypassing the bbb. This application is highly effective, however is also invasive and can require multiple injection sites.

What are the key advantages and limitations of using calcium imaging compared to Electrophysiology for studying neuronal activity?

Calcium imaging is a non-invasive technique that allows for large-scale recordings from multiple neurons simultaneously, enabling the visualization of subcellular calcium dynamics in real time. Calcium acts as an important secondary messenger, so changes in intracellular calcium can reflect neuronal activity, such as action potentials and synaptic input. Calcium imaging also provides high spatial resolution, and with genetically encoded calcium indicators (GECIs), it allows for cell-type-specific and long-term in vivo tracking of neuronal populations.

However, calcium imaging does not measure electrical activity directly. It detects activity indirectly through changes in calcium levels, which introduces a delay and results in lower temporal resolution compared to electrophysiological techniques. In contrast, electrophysiology offers direct, high-temporal-resolution recordings of membrane potentials, action potentials, and synaptic potentials, but is generally limited to single-neuron or small-scale recordings and is often more invasive.

Describe an experimental method used to study memory in research and explain how this the approach helps to assess different aspects of memory.

The Morris water maze is a behavioural technique used in rodents to assess spatial learning and memory. It involves training the animal to find a hidden platform submerged in an opaque pool of water, using visual cues placed around the environment. Over repeated trials, the rodent learns the platform’s location, relying on spatial navigation strategies. Memory is evaluated by measuring metrics such as escape latency, path length, and time spent in the target quadrant during probe trials, when the platform is removed.

This task allows researchers to assess multiple aspects of memory, including: learning acquisition, Short-term memory, Long-term memory and recall and reference memory. This method is used to study hippocampus-dependent spatial memory, as the hippocampus is crucial for encoding, storing, and retrieving spatial information.

Describe the methods by which a researcher would use confocal microscopy to study the anatomical properties of a neuronal system and the types of analyses that can be performed.

Confocal microscopy is used to study the anatomical properties of the nervous system, as it provides high-resolution, optically sectioned images. It works by using a focused laser beam to scan one point at a time across the sample. A pinhole blocks out-of-focus light, resulting in sharper images with improved contrast and resolution. This technique typically involves prepared brain tissue or cultured neurons that have been labelled with fluorescent markers. These may include immunofluorescence, where antibodies are tagged with fluorescent dyes, or genetically encoded markers like GFP (green fluorescent protein). The microscope then performs optical sectioning, collecting thin slices through the tissue, which can be used to create 3D reconstructions of neuronal structures. This allows for detailed anatomical visualisation and quantitative analysis of neurons.