Cellular Neurobiology BIPN140 8 th (last) problem set will be on the class website this weekend; answers will be posted on Monday Review Session with Antonia & Susie: Monday Dec. 5 th 10:00-1:00 pm 3502 Pacific Hall Review Session with all IAs: Wednesday Dec. 7 th 5:00-7:00 pm 3500 Pacitic Hall Final exam: Thursday Dec. 8 th 3:00-6:00 pm Format: 1 hr = 3 rd midterm 2 hr = review of the material of the entire course 2 bonus questions, drawn from the last six lectures
Discovery of the chemical synapse Otto Loewi Henry Dale Nobel Prize, 1936
Activity-dependent transmitter respecification in the developing nervous system 1. Involves addition, loss or switching of neurotransmitters 2. Driven by ion channel misexpression or sensory or motor stimulation 3. Generated by expression or phosphorylation of transcription factors 4. Coupled to corresponding changes in postsynaptic receptor identity 5. Leads to changes in behavior Spitzer, Nature Rev Neurosci 2012
Does activity-dependent transmitter switching occur in the adult mammalian brain? If so, does it lead to changes in behavior?
Hypothalamic circuitry mediating a photoperiod stress response PaVN 3rd 3 rd ventricle icle PaVN PeVN CRF PeVN LPO LPO SCN SCN optic chiasm Retinal ganglion cell axons SCN, suprachiasmatic neurons PaVN, paraventricular neurons PeVN, periventricular neurons LPO, lateral preoptic neurons CRF, corticotrophin releasing factor neurons Dulcis et al.
Photoperiod regulates the number of dopaminergic neurons in the hypothalamus of adult rats Tyrosine hydroxylase-ir - paraventricular nucleus 19L / 5D 150 µm 12L / 12D 5L / 19D TH-IR cells / nucleus (x1000) 40 30 20 10 0 lateral preoptic area paraventricular nucleus periventricular nucleus ** ** ** ** ** 19L/5D 12L/12D 5L/19D * Dulcis et al.
Tyrosine hydroxylase and dopamine are colocalized in the paraventricular nucleus (PaVN) 12L / 12D 5L / 19D TH DA TH DA TH DA 200 µm TH DA Dulcis et al.
Photoperiod also regulates the number of somatostatin neurons in the hypothalamus of adult rats Somatostatin-IR - paraventricular nucleus 19L / 5D 12L / 12D 5L / 19D TH 100 µm SST-IR cells / nucleus (x1000) 30 20 10 0 PaVN PeVN 19L/5D 12L/12D 5L/19D Dulcis et al.
Induction of TH-IR or SST-IR neurons by short or long day photoperiods does not involve adult neurogenesis 12L / 12D PavN 5L / 19D PavN 200 µm TH BrdU TH BrdU BrdU Dentate gyrus BrdU BrdU Dulcis et al.
Disappearance of TH-IR or SST-IR neurons following long or short day photoperiods does not involve apoptosis PaVN & PeVN 19L / 5D 19L / 5D (+ DNase1) 1500 TUNEL DRAQ5 DRAQ5 TUNEL DRAQ5 TUNEL 100 µm TUNEL, DRAQ5 cells / ROI 1200 900 600 300 0 19L: 5D 12L: 12D 5L: 19D ** 5L:19D (DNase1) Dulcis et al.
Somatostatin and dopamine expression in cell bodies and nerve terminals are switched by photoperiod 19L / 5D 12L / 12D 5L / 19D PaVN cell bodies 30 µm Terminals in the PeVN 3 µm Dulcis et al.
Numbers of SST and TH neurons in the PaVN change reciprocally following exposure to long and short day photoperiods SST-IR / TH-IR neurons (x1000) 25 20 15 10 5 0 Somatostatin Dopamine 19L / 5D 12L / 12D 5L / 19D Dulcis et al.
SST 2,4 R and D 2 R expression on corticotrophin releasing factor cells following exposure to different photoperiods SSTR 2,4 CRF D 2 R Labeled cells / section (30 μm) 60 50 40 30 20 10 *** CRF+ SSTR2,4+ SSTR2,4+ D2R+ *** 19L / 5D 12L / 12D 5L / 19D 0 *** ** 19:5 / 5D L:D 12L 12:12 / 12D L:D 5L 5:19 / 19D L:D Dulcis et al.
Corticotrophin releasing factor levels are correlated with photoperiod exposure 80 80 ** CRF level in the CSF (pg/ml) 60 60 40 40 20 20 00 19L 19:5 / L:D 5D 12L 12:12 / 12D L:D 5L 5:19 / 19D L:D * Dulcis et al.
Transmitter and receptor switching SCN input 19L / 5D 12L / 12D 5L / 19D PaVN interneurons SST upregulation SST downregulation Terminals in the PeVN CRF target cells 3rd ventricle DA downregulation DA upregulation SST2/4R D2R SST storage vesicles DA GABA
Measures anxiety Behavioral effect of photoperiod manipulation: elevated plus maze 12L / 12D 5L / 19D L:D (hr) Open arm (sec) Closed arm (sec) 5L/19D 127±3 473±3 12L/12D 74±9 526±9 19L/5D 11±6 589±6 Dulcis et al., Science 2013
Behavioral effect of photoperiod manipulation: forced swim test 5L / 19D 120 Measures depression 19L / 5D Immobility time (sec) / 7 min 100 80 60 40 20 0 19L:5D 12L:12D 5L:19D Dulcis et al., Science 2013
Determining the role of newly dopaminergic neurons in behavioral responses to stress 6-OHDA infusion Ablation of dopaminergic neurons Behavioral tests Behavioral tests, -/+ local dopamine Short-day receptor blockers treatment and respecification of dopaminergic neurons Dopamine Somatostatin Dulcis et al.
Reductions in the numbers of dopaminergic neurons by 6-OHDA can be rescued by photoperiod exposure 6-OHDA TH+ cells / nucleus (x1000) 20 10 20 10 0 0 6 OHDA sham LPO PaVN PeVN LPO PaVN PeVN TH+ cells / nucleus (x1000) 20 15 10 10 5 0 6-OHDA (12L/12D) sham (12L/12D) 6-OHDA, 5L/19D 6-OHDA,19L/5D LPO PaVN PeVN Dulcis et al.
The increase in the numbers of dopaminergic neurons leads to improved behavioral performance in response to stress 100 100 Elevated plus maze Open arm time (sec) 75 75 50 50 25 25 0 0 sham (12L/12D) 6-OHDA (12L/12D) 6-OHDA, 5L/19D 6-OHDA, 5L/19D + local DA receptor blockers 6-OHDA, 5L/19D + ACSF Dulcis et al.
Conclusions Photoperiod exposure regulates the identity of the transmitters expressed in the adult rat hypothalamus The DA SST switch in neurotransmitter specification, with corresponding changes in expression of transmitter receptors, leads to changes in animal behavior, regulating responses to stress Activity-dependent neurotransmitter respecification is a novel form of plasticity in both young and mature brains
Activity-dependent neurotransmitter respecification: a down side?
Forms of neuronal plasticity Classical Plasticity Novel Plasticity Synaptic Strength Synapse Number Neuronal Excitability Neurotransmitter Switching Axon activity activity activity activit y Synapse Dendrite NMDAR AMPAR Na V NT1 NT2 Action potentials
Acknowledgements Spitzer Lab Davide Dulcis Matt Eckler Kyle Jackson Pouya Jamshidi James Lee Hui-quan Li Da Meng Nandu Prakash Christiana Stark Dena Weinberger Stefania Zambetti Collaboration Stefan Leutgeb Funding Ellison Medical Foundation W.M. Keck Foundation NINDS, NIMH