Choline acetyl transferase and neuropeptide immunoreactivities are colocalized in somata, but preferentially localized in distinct axon fibers and boutons of cat sympathetic preganglionic neurons

Abstract

Cholinergic sympathetic preganglionic neurons (SPN) coexpress the biosynthetic enzyme for acetylcholine, choline acetyl-transferase (ChAT), and neuropeptides such as enkephalin (ENK) in their cell bodies. However, it is not clear whether they also coexpress ChAT and neuropeptides in axon fibers and boutons. To explore coexpression of ChAT and neuropeptides in somata and axon processes of SPN, we investigated, using immunohistochemistry, retrograde labeling, confocal analysis, and tridimensional reconstruction, whether ChAT and the peptides neurotensin, methionine-ENK, somatostatin, calcitonin gene-related peptide, and vasoactive intestinal peptide colocalize in somata, axons fibers, and boutons of cat SPN. Practically, complete colocalization for these peptides and ChAT was observed in SPN somata. Conversely, in most instances we observed independent localization of immunoreactivity (IR) for ChAT and the peptides in axon fibers and boutons. The minor colocalization between ChAT- and peptide-IR in preganglionic fibers could correspond to a sequential axonal transport of ChAT and peptides, since we observed coexistence of these transmitters after blocking axonal transport. Contrary to Dale's principle, our results suggest that SPN can synthesize ChAT and peptides in their cell bodies and route them to distinct axon boutons or terminals in sympathetic ganglia. Presence of axon boutons containing either ChAT or neuropeptides lead us to suggest a new neurochemical pattern of cotransmission in sympathetic ganglia based on the concurrent release of transmitters and cotransmitters from distinct presynaptic boutons, rather than in the corelease of these mediators from the same axon process. The possibility that cellular segregation could be transient and depend on functional requirements is considered.

Targeting a neuropeptide to discrete regions of the motor arborizations of a single neuron

“…Our study is consistent with the studies by Sossin et al (Sossin et al, 1990), Hattori et al (Hattori et al, 1991) and Sámano et al (Sámano et al, 2006) in three respects. First, in all four studies, markers were used to identify the neurotransmitters of interests, and the absence or presence of these markers at a specific location was used to indicate the presence of a specific neurotransmitter of interest.…”

“…Thus, it appeared that a dopaminergic neuron was able to form dopaminergic and non-dopaminergic synapses. Finally, Sámano et al (Sámano et al, 2006) used immunohistochemistry to show that ChAT colocalized with other neuropeptides such as methionine-enkephalin, somatostatin and neurotensin in cell bodies of sympathetic preganglionic neurons (SPNs) of cats. Such colocalization was largely absent in the axon fibers and presynaptic terminals of SPNs at the stellate ganglion and sympathetic thoracic trunk of the animal.…”

“…Such colocalization was largely absent in the axon fibers and presynaptic terminals of SPNs at the stellate ganglion and sympathetic thoracic trunk of the animal. Because immunolabeling for ChAT tends to match the immunolabeling of ACh in the central nervous system, Sámano et al (Sámano et al, 2006) suggested that SPNs may synthesize ChAT and neuropeptides in their cell bodies but transport them separately to different locations.…”

Coordination of distinct but interacting rhythmic motor programs by a modulatory projection neuron using different co-transmitters in different ganglia

“…Lastly, the histamine and Crust-MS in the PS neurons might be differentially trafficked to the CoGs and the STG. It is clear in other systems that various neuronal components, including neurotransmitter-containing vesicles, can be differentially trafficked within neurons (Sossin et al, 1990;Hattori et al, 1991;Sámano et al, 2006;Kueh and Jellies, 2012). Regardless of the mechanism(s) involved, our data strongly support the hypothesis that a single modulatory neuron can use its co-transmitters differentially to modulate three spatially distinct target networks.…”

“…Dale's principle (Dale, 1935;Eccles et al, 1954;Eccles, 1976) proposed that all neuronal co-transmitters are uniformly distributed and co-released. While this may be true for some neurons, others are clearly capable of differentially packaging and trafficking neuroactive compounds to distinct compartments (Sossin et al, 1990;Hattori et al, 1991;Sámano et al, 2006;Kueh and Jellies, 2012) and/or differentially releasing co-transmitters in response to different activity patterns (Whim and Lloyd, 1989). Even when coreleased, co-transmitter actions can be compartmentalized via the differential distribution of their receptors (Marder et al, 1995;Thurimulai and Marder, 2002).…”