DEVELOPMENT I: PROLIFERATION, MIGRATION Today’s reading: Chap. 7( ); 23( ) Wednesday: Chapter 23 ( ) AMHERST COLLEGE INTRODUCTION TO NEUROSCIENCE MONDAY, FEBRUARY 4, 2008 Neuroanatomy questions 1.What is an exception to the rule that “ganglia” are in the PNS? 2.Place in rostro-caudal order: Inferior colliculus Thalamus Medullary respiratory center 3.The “medial forebrain bundle” is, as the name suggests, a bundle of axons in the medial forebrain. Why isn’t it called the “medial forebrain tract”?

Tomorrow - 7:00 AM to 8:00 PM Bangs Community Center (Behind Panda East & Rao’s)

Outline of development

Proliferation Fertilized egg Whole organism (single cell) neurons Question: how many rounds of cell division? 2x2x2x2x…. = 10x10x10x….x10 Log10 (2) =3.3, i.e.10 = 2 3.3, so =(2 3.3 ) 11 = 2 36 →

Proliferation Fertilized egg Whole organism (single cell) neurons Question: how many rounds of cell division? →

Early vertebrate development Neural groove → neural tube. Vertebrate CNS = hollow organ Fig. 7.8 Neural crest: -Dorsal root ganglia -Autonomic ganglia -PNS myelin CNS Notochord

Early vertebrate development Neural groove → neural tube. Vertebrate CNS = hollow organ Fig. 7.8

Vertebrate brain development: 3 subdivisions Anterior neural tube → 3 brain ‘vesicles’ Fig. 7.9, 7.10, 7.13 → Basal Line of Thalamus ganglia “secondary fusion”

Vertebrate development: 3 brain subdivisions Anterior neural tube → 3 brain ‘vesicles’ Fig. 7.9, 710 →

Development of the retina Retinal ganglion cells develop after the optic cup is formed. Their axons grow from the retina to the diencephalon and midbrain. Is “optic nerve” a consistent name for the bundle of axons connecting the retina to the rest of the brain? Is “ganglion” cell a consistent name for neurons in the retina? Fig. 7.10,11

Features of proliferation Cell divisions occur in ventricular zone Nucleus moves to marginal zone for “S” phase (synthesizing DNA for next division) Cell becomes postmitotic (has its “birthday”) after horizontal cleavage Fig. 22.2

Features of proliferation Fig. 22.2

1. Technique: Autoradiography 3 H = tritium, hydrogen atom with 2 extra neutrons; it undergoes radioactive decay 3 H -thymidine (a nucleotide that is one component of the genetic material, DNA) is used to study cell “birthdays” (i.e. date of final cell division) 3 H-proline, an amino acid that is one component of proteins, is used to trace neuronal pathways.

1. Technique: Autoradiography

Analysis of cell birthdays Label monkey fetus with 3 H-thymidine at E33 or E56 Wait until animal matures, then perform autoradiography Pia Ventricle Exposed to label at E33 Exposed to label at E56 Conclusion: Postmitotic neurons migrate towards the pia, migrating past neurons that migrated previously.

Analysis of cell birthdays Label monkey fetus with 3 H-thymidine at E33 or E56 Wait until animal matures, then perform autoradiography Pia Ventricle Exposed to label at E33 Exposed to label at E56

When a monkey fetus is exposed to 3 H-thymidine at embryonic day 33, shouldn’t all dividing cells take up the label, including cells whose progeny will be dividing later, e.g. at day 56? In that case, why is there only a narrow band of label in the animals exposed at day 33 – why doesn’t it extend all the way up to the pia? Technical question: Exposed at E33 Exposed at E56

Features of mammalian cortical development Dividing neuroblasts proliferate in the ventricular zone At some point (before birth in mammals) cells stop dividing – i.e. they have their “birthday,” except for a very few neuronal stem cells They immediately migrate towards the marginal zone, following radial glial cells The order of migration is “inside out,” i.e. newly born neurons migrate past previously migrated ones to a point nearer the pia Large neurons are born earlier than small neurons Glial cells retain the capability of dividing throughout the life of the animal

Neurons and the “cell cycle” Are neurons able to divide, or are they “post-mitotic?” (Mitosis = cell division; post-mitotic = can no longer divide) Look for “mitotic figures” in slices of brain tissue But, there’s a problem… Modern methods –Autoradiography –Bromodeoxyuridine (BRDU) Like DNA Fluorescent

Neurons and the “cell cycle” Are neurons able to divide, or are they “post-mitotic?”

2. BRDU + specific neuron label Green=BRDU Red=neuron-specific stain

Neuronal differentiation: Control of gene expression cytoplasm nucleus membrane cytoplasm nucleus membrane

Neuronal differentiation: Control of gene expression

AMPAdenosine monophosphate cAMPCyclic AMP CBPCREB binding protein CREBcyclic AMP response element binding protein KinaseEnzyme that adds a phosphate to another molecule PKAProtein kinase A Pol II Polymerase II – enzyme that transcribes DNA into RNA PO 4 Phosphate TATAsequence of thymidine, adenine, etc. that binds Pol II

cytoplasm nucleus membrane

Introduction to cell death 2 – 3 times overproduction of cells during development Occurs in many parts of the body Two distinct kinds: –Programmed (apoptotic, “suicide”) –Necrotic (“murder”) In invertebrates, specific identified cell always dies at a particular time Cell death program can be activated in adults, e.g. neurodegenerative diseases