Retrograde tracing
Encyclopedia
Retrograde tracing is a research method which is used in neuroscience
to trace neural connections from their point of termination (the synapse
) to their source (the cell body). The opposite technique is anterograde tracing
, which is used to trace neural connections from their source to their point of termination (i.e. from cell body to synapse). Both the anterograde and retrograde tracing techniques are based on the visualization of the biological process
of axonal transport.
The anterograde and retrograde tracing techniques allow the detailed assessment of neuronal connections from a single population of neurons to their various targets throughout the nervous system
. These techniques allow the "mapping" of connections between neurons in a particular structure (e.g. the eye
) and the target neurons in the brain
. Much of what is currently known about connectional neuroanatomy
was discovered through the use of the anterograde and retrograde tracing techniques.
Another technique involves injecting special "beads" into the brain
nuclei of anesthetized animals. The animals are allowed to survive for a few days and then euthanized. The cells in the origin of projection are visualized through an inverted fluorescence microscope
.
Neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
to trace neural connections from their point of termination (the synapse
Synapse
In the nervous system, a synapse is a structure that permits a neuron to pass an electrical or chemical signal to another cell...
) to their source (the cell body). The opposite technique is anterograde tracing
Anterograde tracing
In neuroscience, anterograde tracing is a research method which is used to trace axonal projections from their source In neuroscience, anterograde tracing is a research method which is used to trace axonal projections from their source In neuroscience, anterograde tracing is a research method which...
, which is used to trace neural connections from their source to their point of termination (i.e. from cell body to synapse). Both the anterograde and retrograde tracing techniques are based on the visualization of the biological process
Biological process
A biological process is a process of a living organism. Biological processes are made up of any number of chemical reactions or other events that results in a transformation....
of axonal transport.
The anterograde and retrograde tracing techniques allow the detailed assessment of neuronal connections from a single population of neurons to their various targets throughout the nervous system
Nervous system
The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...
. These techniques allow the "mapping" of connections between neurons in a particular structure (e.g. the eye
Human eye
The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...
) and the target neurons in the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
. Much of what is currently known about connectional neuroanatomy
Neuroanatomy
Neuroanatomy is the study of the anatomy and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defined nervous systems, and thus we can begin to speak of...
was discovered through the use of the anterograde and retrograde tracing techniques.
Techniques
Retrograde tracing can be achieved through various means, including the use of viral strains as markers of a cell’s connectivity to the injection site. The pseudorabies virus (PRV; Bartha strain), for example, may be used as a suitable tracer due to the propensity of the infection to spread upstream through a pathway of synaptically linked neurons, thus revealing the nature of their circuitry.Another technique involves injecting special "beads" into the brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
nuclei of anesthetized animals. The animals are allowed to survive for a few days and then euthanized. The cells in the origin of projection are visualized through an inverted fluorescence microscope
Fluorescence microscope
A fluorescence microscope is an optical microscope used to study properties of organic or inorganic substances using the phenomena of fluorescence and phosphorescence instead of, or in addition to, reflection and absorption...
.