The Origin of Afferents to the Brainstem Core

Abstract

We now discuss the inputs to brainstem core neurons as revealed by morphological and electrophysiological studies. Since neurons in the classical brainstem reticular fields (either identified immunohistochemically as cholinergic or using transmitters as yet unidentified) have morphological and functional characteristics that are dissimilar to monoaminergic neurons, these two groups of elements are dealt with separately. Although cholinergic nuclei of various species also contain a minority of monoaminergic cells, and some monoaminergic nuclei possess a certain number of cholinergic cells (see Chapter 4), the presence of ACh or of one of the three monoamine transmitters defines one or the other of these two nuclear categories. The parabrachial nucleus, i.e., the caudal part of the neuronal group that surrounds the brachium conjunctivum and contains both cholinergic and aminergic neurons, is conventionally included among brainstem reticular nuclei. An initial section (3.1) discusses extrabrainstem sources of reticular afferents, and a subsequent section (3.2) examines brainstem sources of reticular afferents, including intrinsic reticuloreticular connectivity. Details of brainstem oculomotor system anatomy, which critically involves the reticular formation, are reviewed in Chapter 10 in conjunction with discussion of the physiology of the saccade-generating system. The final section (3.3) of this chapter discusses the afferents of monoaminergic nuclei.