1. Histological and immunochemical staining methods

Brains of different origin and fixation (perfusion-fixed, frozen-fixed) are cut into sections and stained on the basis of their chemical (e.g., Nissl, myelin), enzymatic (e.g. acetylcholine-esterase, cytochrome-oxidase), or immunological properties (e.g. protein epitopes).

Figure: Frontal section through the brain of a gerbil stained for myelin.

2. Anterograde and retrograde tract tracing

Neuronal tracing substances (e.g., biocytin, dextranamines) are injected by pressure or iontophoretically into the brain region of interest. Then these tracers are transported, via the axonal transport of the cell, towards the cell body (retrograde transport; origin of a projection) or towards the presynapses of the cell (anterograde transport; target of a projection).

Figure: Connectivity pattern within gerbil auditory cortex after injection of biocytin into the primary auditory field AI

3. Intracellular and juxtacellular cell staining

Chromogenes, usually neuronal tracers like biocytin or Lucifer yellow, are microiotophoretically injected via small glass pipettes into a cell (intracellularly) or its close proximity (juxtacellularly).

Figure: Intracellularly filled pyramidal neuron in the auditory cortex of the gerbil.

4. 2-deoxy-glucose method

The 2-deoxy-glucose method (Sokoloff et al., 1977, J. Neurochem, 28:897-916) is used for mapping neuronal, i.e. metabolic, activity in the brain. Animals are injected with radioactively labeled glucose-analogs such as 2-deoxy-glucose or 2-fluoro-2-deoxyglucose which distribution can be detected autoradiographically. Due to the tight coupling of neuronal activity and glucose consumption the resulting maps provide information about the spatial patterns of neuronal activity in the brain.

Figure: 2-deoxy-glucose autoradiograph from a horizontal section of the brain of a Mongolian Gerbil.

5. Thallium Autometallographie

Thallium autometallography is a novel method for mapping neuronal activity. This technique, which has been developed in our department, is based on the fact that in neurons the rate of K+-uptake increases with increasing neuronal activity. The K+-analog thallium is used as a tracer for mapping the activity-dependent changes in K+-uptake. We modified a routine histochemical method for the detection of heavy metals in the brain, the autometallographic method or Timm-technique, to specifically detect thallium. Thallium autometallography can be used for mapping thallium uptake with cellular and subcellular resolution at the light and electron microscopical level.

Figure: Pattern of thallium uptake in cerebral cortex of an awake behaving rat as determined by thallium autometallography