The DORSAL NORADRENERGIC BUNDLE (DNAB) and the VENTRAL NORADRENERGIC BUNDLE (VNAB) are the principal NORADRENALINE-containing systems that arise in the PONS and MEDULLA to innervate a variety of FOREBRAIN sites. They are often referred to simply as the dorsal bundle and ventral bundle respectively. Originally described by Ungerstedt (1971), they were initially thought of as being relatively compact, but later studies revealed them to be less so than had been thought.
The ventral bundle arises from the lateral tegmental noradrenaline containing cell groups A1-A5 (see CLASSIFICATION OF DAHLSTRÖM AND FUXE) and is sometimes therefore referred to as the lateral tegmental noradrenergic system. These cell groups lie relatively deep in the brain: cell group A1 for example is close by the AREA POSTREMA and NUCLEUS OF THE SOLITARY TRACT, while A2 lies near the DORSAL MOTOR NUCLEUS OF THE VAGUS. The axons of all of these cell groups collect into the ventral bundle, which passes below the SUPERIOR CEREBELLAR PEDUNCLE before ascending to join the MEDIAL FOREBRAIN BUNDLE. The principal targets of the ventral bundle are subcortical: the largest projections are to the HYPOTHALAMUS, AMYGDALA and the SEPTAL NUCLEI, though there are other targets, including parts of the THALAMUS and the NUCLEUS ACCUMBENS, and many brainstem targets. Functionally, the ventral bundle has been associated with the transmission of autonomic information and destruction of it is known to lead to deficits in activities such as FEEDING, DRINKING and SEXUAL BEHAVIOUR.
The dorsal bundle arises principally from cell groups A6 and A7. The A6 group is in the LOCUS COERULEUS, while A7 is referred to as being subcoeruleal.
The axons of these neurons collect into the dorsal bundle and also pass through and below the superior cerebellar peduncle (though on a course different to that of the ventral bundle). Through the MIDBRAIN they take a course significantly more dorsal to that of the ventral bundle before joining the medial forebrain bundle. Dorsal bundle fibres leave here via a variety of routes (the MAMMILOTHALAMIC TRACT, DIAGONAL BAND OF BROCA, STRIA MEDULLARIS, STRIA TERMINALIS, FORNIX) to innervate sites in the thalamus, amygdala, septal nuclei and nucleus accumbens (as well as brainstem sites) that also receive input from the ventral bundle. However, the principal targets of the dorsal bundle are the HIPPOCAMPUS and CEREBRAL CORTEX which do not receive input from the ventral bundle. Functionally, the dorsal bundle has been associated with ATTENTION and AROUSAL. It is noteworthy in this context that the locus coeruleus has a very strong CARDIOVASCULAR SYSTEM input.
The dorsal and ventral bundles interact with each other and with other nuclei in the ASCENDING RETICULAR ACTIVATING SYSTEM and are involved in discriminably different functions. What remains most remarkable about them however is that such a small number of neurons—only some 2000 in the rat locus coeruleus—should innervate such a wide area of tissue in the central nervous system.
Reference
Ungerstedt U. (1971) Stereotaxic mapping of the monoamine pathways in the rat brain. Acta Physiologica Scandinavica, suppl. 367: 1–48.
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