Axon gudiance & synapse formation 4 lecture

Instructor encourages students to reflect on Monday's lecture.
Learning Outcomes:
- Importance of using learning outcomes to assess knowledge.
- Example question posed: "Can I explain how inductive signals establish neural identity?"
Active Learning Encouragement:
- Students are encouraged to identify misunderstandings through self-reflection.
- Students can seek clarification through emails to the instructor.

Coverage of the following topics:
- Molecular mechanisms of growth cone guidance.
- Signups formation and elimination.

Agreement on neuron birth and specification.
Axon emission and growth:
- Growth cones play a crucial role in axon guidance by responding to various cues.
Importance of refining synaptic connections:
- Branches that are useful are maintained, while weak or unnecessary branches are eliminated to strengthen synapses.

Growth Cones Role:
- Neurons emit axons that grow toward their targets, guided by growth cones responding to molecular cues.
- Synapses are formed through selective processes not entirely competitive; they are cooperative instead.
Cooperative Process Explained:
- Suggests that many neurons may die, and not all connections will be formed.
- The interconnectedness of neurons allows for shared guidance cues.

Importance of neurotrophic factors in neuron target interactions:
- Neurons have receptors to respond to neurotrophic factors from target tissues.
- Communication occurs in a polarized and localized manner, crucial for synapse formation.
- Cytoskeletal remodeling aids in the movement and positioning of synaptic components.

Discussion on vesicular trafficking (anterograde and retrograde) essential for synaptic activity:
- Importance of interactions between the soma and synapse for determining neuron survival.
- Docking secretory vesicles involves local cytoskeletal components.
Postsynaptic Density (PSD) Development:
- Critical for recruiting necessary receptors for effective synaptic transmission.

Dendrite Guidance:
- Dendrites explore their environment to establish effective neuron connections.
- Cell adhesion mechanisms like "dashcam" in Drosophila aid specificity in connections.
Diversity of Adhesion Molecules:
- Potential connections numbered in tens of thousands enhance the complexity.
- Mechanisms distinguish between self and non-self connections critical for proper branching.

Receptor Clustering:
- The necessity of receptor clustering at specific sites for effective neurotransmission.
- Role of muscle-specific kinase (MuSK) in clustering acetylcholine receptors at neuromuscular junctions.
Experimentation with MuSK Knockouts:
- Observations show that absence of MuSK leads to diffuse receptor localization, preventing proper synaptic connection formation.

Differential receptor interactions with neurotrophic factors (NGF, BDNF, etc.):
- NGF interaction with Track A promotes neuron survival.
- BDNF predominantly interacts with Track B, affecting neuron survival and differentiation.
- P75 receptor is associated with pro-death signaling when neurotrophic factor levels are inadequately low.
Experimental Evidence of Pruning Mechanism:
- Use of injected dyes to visualize whether neuron branches maintain connections during development.

Histological Observations in Organ Development:
- Postnatal observations show reduced successful synapse connections over time due to pruning of weaker synaptic connections.

The historical significance of developmental biology:
- Reference to pioneering experiment by Victor Hamburger showing correlation between limb development and neuron survival.
- Emphasis on understanding that neurodegenerative diseases relate back to developmental processes, not merely age-related decline.

Instructor encourages engagement and preparation for the next discussion by reading relevant papers and generating questions.
Importance of understanding all concepts covered to grasp neurological development and disorders effectively.