Revised guides for organ sampling and trimming in rats and mice: BRAIN

BRAIN

Species:	Rats and Mice
Organs:	Brain Cerebellum Cerebral meninx Chorioid plexus Cranial nerve
Localizations:	1) Cerebrum at the optic chiasm 2) Cerebrum at the base of the posterior hypothalamus 3) Midcerebellum and medulla oblongata Optional: 4) Pons at the middle of its protrusion 5) cranial cervical cord
Number of sections:	3 (4)
Direction:	Transverse
Remarks:	Embedded with the anterior faces down. To achieve accurate brain weights, the spinal cord should be cut off at a consistent level.

Brain, lateral view.

Brain, ventral view.

Brain, localization 1, cerebrum.
Brain, localization 2, cerebrum.

Brain, localization 3, cerebellum
and medulla oblongata.
Brain, optional localization 4, cerebrum and pons.

Abbreviations used in the above images: Ac: anterior commissure, C: cerebellum, Cc: cerebral cortex, Cca: corpus callosum, H: hypothalamus, Hc: hippocampus, Mo: medulla oblongata, O: optic chiasm, P: pons, Sr: striatum, T: thalamus.

Coronal Brain Matrix System
(supplier: A. Semrau GmbH und Co, 45549 Sprockhoevel, Germany).

Unless the scope of examinations in neurotoxicity studies is extended, it is advised to use the above mentioned brain sections for the morphological screening in all rodent studies concerned.

Transverse sections of the brain are required to assess whether the findings are distributed uni- or bilaterally and symmetrically or asymmetrically. The areas of the brain known to be susceptible to neurotoxicity, including oncogenicity, are: the cerebral and cerebellar cortex, hippocampus, basal ganglia, thalamus, hypothalamus, midbrain, pons and medulla oblongata. Routinely, three transverse sections are obtained:

the first section at the level of optic chiasm including the basal ganglia, septum, cortex, anterior hypothalamus;
the second section at the level of hippocampus containing the cortex and brain stem at the transition of diencephalon to mesencephalon and
the third section containing the cerebellum and brain stem (medulla oblongata).

Location 4 is recommended for special investigations of the pons.

To achieve precise vertical cuts, brain matrix moulds can be used. Different sizes are available for different laboratory species. For rodents, the brain can be sliced at 1 mm intervals.

A sample of the cranial cervical cord can be removed together with the brain (location 5). Alternatively, it can be taken together with the cranial vertebral column to avoid artifacts (see spinal cord).

Trimmed specimens should not be stored in alcohol for extended periods during routine processing to avoid artifactual vacuolation.

See also:
Spinal cord
Introduction

References

	Dorman DC, Brenneman KA, Bolon B (2002) Nervous system. In: Haschek WM, Rousseaux CG, Wallig MA (eds) Handbook of toxicologic pathology, 2nd edition, Vol 2. Academic Press, San Diego New York Boston, pp 509–537
	Krinke GJ (1989) Neuropathologic screening in rodent and other species. J Am Coll Toxicol 8: 141–146
	Paxinos G, Watson C (1997) The rat brain in stereotaxic coordinates. 3rd edition. Academic Press, San Diego London
	Schäppi U, Krinke G (1991) Die Erfassung toxischer Wirkungen am Nervensystem. In: Hess R (ed) Arzneimittel-Toxikologie. Georg Thieme Verlag, Stuttgart, New York, pp 238–258
	WHO (1986) Principles and methods for the assessment of neurotoxicity associated with exposure to chemicals. In: Environmental health criteria 60. World Health Organization, Geneva

Guidelines overview

	EMEA	FDA	MHW	EPA	NTP	OECD	STP
Brain	+	+	+	+	+	+	+
Cerebellum	+			+