Gallery: Fluorescence Microscopy

The images in this gallery have been obtained with a confocal LSM (Laser Scanning Microscope) or by conventional fluorescent microscopy. In some cases, the usual "coding" of RGB (red, green, blue) for each channel has been changed to different colors.

 

Tissue / Cell types / Morphology

Brain / CNS

 

The brain (central nervous system, CNS) of hihgher vertebrates can be roughly divided into 4 parts (Note: the PNS is not part of this description):

 

Cerebrum

Cerebellum

Diencephalon

Brain stem

Neuron

The main cell types characterizing the CNS are essentially neurons and glial cells, whereby the first are regarded as the cellular substrate of the cognitive abilities of the CNS. The basic morphology of a neuron consists of three main parts:

  1. The bulbous part of a neuron is called the soma (or perikaryon), and contains the cell nucleus. The word soma is Greek, meaning "body".
  2. From the soma, one axon ( a “cable-like” projection), often myelinated, extends, which propagates signals to other cells (neurons, muscle, etc.). The axon forms synapses at its terminal part, when it its “contacting” other cells.
  3. The soma is also covered by dendrites, which in most case are the “receiving” entity, which are connected to axon terminals of other neurons.

It was long postulated, that in the adult mammalian brain, no new neurons are "born". However, it has been shown in humans and in mice that this dogma has been wrong.

"This study was undertaken to investigate whether neurogenesis occurs in the adult human brain, in regions previously identified as neurogenic in adult rodents and monkeys. Human brain tissue was obtained postmortem from patients who had been treated with the thymidine analog, bromodeoxyuridine (BrdU), that labels DNA during the S phase. Using immunofluorescent labeling for BrdU and for one of the neuronal markers, NeuN, calbindin or neuron specific enolase (NSE), we demonstrate that new neurons, as defined by these markers, are generated from dividing progenitor cells in the dentate gyrus of adult humans. Our results further indicate that the human hippocampus retains its ability to generate neurons throughout life." [Eriksson PS, Perfilieva E, Bjork-Eriksson T, Alborn AM, Nordborg C, Peterson DA, Gage FH.; Nature Medicine 1998 Nov;4(11) Source » PubMed ]

The numbers of neurons varies extremly between species: the common fruit fly has about 100.000 neurons, whereas it is estimated that the human brain has about 1014 (100 billion) neurons. However these are estimates, nobody ever counted all the neurons, or delivered a plausible concept how to estimate their number.
But, just to remember you, how wrong sience can be: it was printed in almost every biology / medicine text book, an often used question in tests, and broadly regarded as a fact for decades - that the human genome has about 100.000 genes. Until of course, the genes where actually counted: turns out, their number is about +/- 25.000 in humans and +/- 30.000 in mice.

Astrocyte

Astrocytes belong to the 3 types of glial cells in the CNS (the others are microglia and oligodendrocytes). They are also known as astroglia and are exhibt usually a star-shaped mmorphology, with many processes extending from the soma. Astrocytes can be identified histologically since they express the intermediate filament glial fibrillary acidic protein (GFAP).
Astrocytes perform a plethora of functions (and the list is constantly growing:
biochemical support of neurons and other cell ytpes,
support of endothelial cells which form the blood-brain barrier,
a major role in the repair and scarring process of the brain and spinal cord following mechanical / inflammatory injuries,
a "guidance" for growing neurons / axons during the development of the brain.

Previously in medical science, astrocytes have not been given an active role in the information processing activity of the brain, but this view has recently been challenged.

Microglia

Microglia are a cell type, that is only found in the CNS (Central Nervous System; per human definition: brain and spinal cord). Usually microglial cells are in a so called ramified state, in which they are immunologically inactive. However they can be “activated” via various triggers (all caused by some kind of brain injury):

  1. elevated levels of pro-inflammatory cytokines (a combination of lipopolysaccharide (LPS) and interferon-gamma is one of the most effective)
  2. neuroinflammatory and neurodegenerative diseases, including Parkinson’s disease, Multiple Sclerosis, Alzheimer’s, and Huntington’s disease
  3. physical injury

Once activated, microglia assume an amoeboid (round, oval) morphology, and display a behavior similar to macrophages. They act as antigen-presenting, phagocytic, and cytotoxic cells, all three a hallmark of cells of the immune system.

The name microglia was first (1920) introduced by Pio del Rio-Hortega (1882 – 1945). Since the function and ontology of microglia was unknown at that time, and furthermore, the cells of the brain where divided into two types: neurons and “others”, which were termed by the generic expression “glia” (e.g. astroglia and oligodendroglia ), the term microglia was a reference 1. to their shape 2. to their obviously non-neuronal characteristics.

Hepatocyte

Hepatocyte is the terminus technicus for parenchymal liver cells, derived from the Greek word "hepar" which translates to liver (see also Hepatitis with the suffix "-itis", which, in medicine, has the general meaning "inflammation"). Hepatocytes are the major cell type of the liver (more than 80%), and they are responsible for a plethora of metabolic functions.

Fibroblast

A cell type that is found in various so called "connective tissue"; the definition is rather difficult, since the term mainly refers to the ability of fibroblasts to synthesize and maintain the extracellular matrix of many organs. The term is a composition of "fibro-" from Latin "fibra" meaning fiber and "-blast" from Greek "blastos", meaning germ, bud.

Protein / Enzyme

The (confocal) fluorescence microscopy images in this gallery are mostly about connexin (which form gap junctions), nitric oxide synthase (iNOS, bNOS, eNOS), NF-KappaB (NFkB) and cytoskeleton (tubulin, neurofilament). Using a primary antibody (which binds to the protein) and a secondary antibody, labeled with a fluorochrome, which binds to the primary antibody, the images where obtained.

Connexin

Connexin proteins rank among a group of transmembrane proteins, which incorporate into the cell membrane to form channels. Six connexins are clustered to form a connexon, a structure, with a pore in the center, as one half of the channel. Two connexons in neighbouring cells connect to so called "gap junctions". The opening of this channel is controlled by the cell, and the channel is permeable for low-molecular substances (ions, small molecules, very, very small proteins).

NF-kB

NF-kB (Nuclear Factor Kappa-light-chain-enhancer of activated B Cells) is a transcription factor, e.g. a protein which interacts with the DNA to enhance / suppress the expression of genes. NF-kB (also sometimes NF-kappaB) is found in almost all animal cell types and belongs to the family of "rapid-acting" primary transcription factors (its activity can be triggerd within minutes).

GFAP

Glial Fibrillary Acidic Protein (GFAP) is a protein, first discovered in 1971. It belongs to a class of proteins called intermediate filaments (prominent members are tubulin (which forms microtubules), neurofilament, vimentin, ...), whose primary function is the formation of the cytoskeleton (the "skeleton" within the cytoplasm of all cells). The cytoskeleton is responsible for the shape, intracellular transport and cellular division (e.g. mitosis).
In the adult CNS, GFAP is almost exclusively expressed in astrocytes, and is thus regarded as a very reliable cellular marker.

Tubulin

The most common members of the tubulin family are alpha-tubulin and beta-tubulin, which, as dimers, make up microtubules. Microtubules have a diameter of 25 nm and a length between 200 nanometers and 25 micrometers (which is close to the diameter of the largest eukaryotic cells).
Besides their role as part of the cytoskeleton, they have the notable function of forming the mitotic spindle, used during cell divison to segregate the chromosomes.

Neurofilament

Neurons in can be labeld by antibodies against neurofilaments. Neurofilaments, as part of the cytoskeleton, belong to a class of proteins called intermediate filaments which are about 10 nanometer (10nm) in diameter, and are tghus smaller than microtubules. Neurofilaments are expressed exclusively in neurons – and mostly within the axon.