Chapter 5 research Experimental Ablation Definition The removal - PDF document

Methods and strategies of Chapter 5 research

Experimental Ablation • Definition – The removal or destruction of a portion of the brain of a laboratory animal; presumably, the functions that can no longer be performed are the ones the region previously controlled. • Distinction between brain function and behavior – Destroy a nucleus in a mice, trying to prove it involves visual information processing, how to test?

Producing brain lesions • Tissue removal/ aspiration – Outer part of the brain, cortex • Radio frequency lesions (RF) – Destroy both neural cell bodies and axons bypassing • Excitotoxic lesions – Destroy neural cell bodies only • Neurochemical lesions (6-hydroxydopamine, 6- HD) – Selectively destroy noradrenergic or dopaminergic neurons • The Importance of sham lesions, (placebo)

Stereotaxic surgery

Histological Methods • Histological methods are used to verify the placement of a lesion – Perfuse (to remove blood) – Fix in formalin (to solidify tissue and prevent autolysis) – Slice into sections – Stains (to highlight selective neural elements) • Golgi stain—stains full cell (membrane) • Nissl stain—stains cell bodies (RNA) • Weil stain—Stains axon (Myelin) • Electron microscopy – Transmission electron microscope – Scanning electron microscope • Confocal laser scanning microscope

Tracking neural connections • Neurons send outputs • Efferent (exiting) axons – Anterograde labeling (cell bodies to axons to terminal buttons) – Eg.PHA-L – Use immunocytochemistry with antibodies to proteins or peptides • Neurons receive inputs • Afferent (arriving) axons – Retrograde labeling (from axons to cell bodies) – Eg. Flourgold

Visualizing a living human brain • To see anatomy & functioning • Detect tumors or lesions or abnormalities – Computerized tomography (CT) uses an X-ray beam to scan the brain from all angles, there scans are then summarized in an image of the skull and brain – Magnetic Resonance Imaging (MRI) uses a magnetic field and radio waves to excite hydrogen molecules, the resulting information is combined to form an image of tissue • Which one has higher resolution? • Other brain imaging technique: EEG, PET

Alzheimer's brain

Human Brain Imaging • The PET scan measures metabolic activity in brain – Human subject is injected with radioactive substance, which is taken up by brain cells – As the redioactive molecules decay they emit positrons that can be detected by a scanner – A PET scan indicates the relative activity of different brain regions during mental states • Functional MRI (fMRI) scans detect the level of oxygen in brain blood vessles – Current fMRI scanners have a higher resolution than do PET scanners

Recording neural activity • Microelectrodes record single neuron activation, acute or chronic • Macroelectrodes record summated electrical activity of large regions of brain • Surface electrodes placed on human scalp are used to record brain activity • Electroencephalogram: EEG • Events related potential: ERP (stimulus locked EEG)

Recording metabolic & synaptic activity • The 2-deoxyglucose (2-DG) methods measures relative glucose utilization – 2-DG cannot be metabolized, is trapped in cells and accumulates – Radioactive 2-DG is then quantitaed using autoradiography • FOS (nuclear protein) is expressed when a neuron is activated – Neuronal activation is associated with activation of genes in the neuron nuleus; can localize Fos within the nucleus, indicate relative degree of activation

Secretions & Stimulation of the Brain • The secretion of neurotransmitter within a discrete brain region can be measured using microdialysis , then analyze its contents • Neurons in a region can be artificially activated to assess the role of a region in behavior – Electrical stimulation involves passing electrical current through a wire inserted into brain – Chemical stimulation can involve infusion of small amount of an excitatory amino acid such as glutamate into a region, microiontophoresis

Behavioral effects of electrical brain stimulation • Transcanial magnetic stimulation (TMS) – Stimulation of the cerebral cortex by means of magnetic fields produced by passing pulses of electricity through a coil of wire placed next to the skull; interferes with the functions of the brain region that is stimulated. – Eg, primary somatosensory cortex and pain localization

Localization of neurotransmitters • Three approaches to the localization of a neurochemicals in the brain: – Localize the chemical • Peptides or proteins localized directly via immunocytochemistry – Localize the enzyme that produces the chemical or neurotransmitter • If it is not a peptide (or protein) can still use stain with antibody to the enzyme – Localize the messenger RNA involved in chemical synthesis, in situ hybridization • Peptides & protein with tracers, anterograde or retrograde (chemicals + connections in double labeling)

Localizing particular receptors • Receptors can be localized in brain tissue using • Autoradiography – Sections of brain are exposed to solutions containing a radioactive ligand (chemical that binds), washed, and placed on film – The resulting file images show spots at which radioactivity exposed to the film • Immunocytochemistry – Antibodies are developed for the receptor protein, are tagged with a fluorescent dye – The tissue is exposed to the antibody/dye – The section is then examined under a microscope for the presence of dye in specific regions

Genetic Methods • Genetic research methods seek demostration the linkage between genes and behavior – Twin studies examine the impact of varying degress of genetic similarity on behavioral similarity – Adoption studies examine a trait similarity of an adopted person compared to their adopted parents and their biological parents – Targeted mutations involve the insertion of a defective (knockout) genes into the chromosome of mice – Antisense oligonucleotide uses modified strand of RNA or DNA that binds with a specific molecule of mRNA and prevents it from producing its protein