Postnatal development of brainstem cholinergic inputs to the dorsal lateral geniculate nucleus of the domesticated ferret, Mustela putorius furo

Abstract

The ferret dorsal lateral geniculate nucleus (dLGN) undergoes two periods of retinal afferent segregation during postnatal development. The first establishes the eye-specific laminae, A and A 1, and the second establishes ON/OFF sublaminae within laminae A and At. In contrast to eyespecific segregation, which seems to rely only on presynaptic activity, ON /OFF sublamination requires both pre- and postsynaptic activity. Because of its dependence on postsynaptic (relay cell) activity, sub lamination may be influenced by extra retinal inputs which alter relay cell excitability. We have examined the postnatal development of cholinergic brainstem inputs to the dLGN to determine whether these inputs arrive in time to influence sublamination and whether the cholinergic innervation is present in laminar zones (i.e., whether it might target relay cells). Choline acetyltransferase (ChA1) immunoreactivity is not detected in the dLGN until a few days after the second postnatal week Gust after sublamination begins), at which time it can be seen in both A and C laminae. ChA T labeling increases in intensity until two days before the end of the fourth postnatal week (when ON/OFF sublamination is complete), when it drops dramatically throughout the dLGN . ChAT labeling returns a few days later, but appears in the interlaminar and intersublaminar zones instead of within the A and C laminae. However, the pattern of ChA T labeling reverses once more, so that in the adult, ChA T labeling appears in the A and C laminae and is relatively absent from interlaminar zones. Acetylcholinesterase (AChE) labeling in the dLGN shows a similar ontogenetic pattern and time course. Retrngrade labeling of brainstem cholinergic nuclei demonstrates that these inputs are in place in the dLGN after the second postnatal week. Thus, cholinergic inputs to A and A 1 laminae of the ferret dLG N do arrive in time to influence ON/OFF sublamination.