Phenotypic plasticity in adult sympathetic neurons: changes in neuropeptide expression in organ culture.

Abstract

Vasoactive intestinal peptide (VEP)-like immunoreactivity is present at low levels in the superior cervical ganglion of the adult rat, where immunostained neural processes, but only an occasional immunostained cell body, are found. However, when ganglia are maintained for 24 or 48 hr in organ culture, their content of VIP-like immunoreactivity increases 6-or 31-fold, respectively. When examined at 24 hr, the increase in VIP-like immunoreactivity is totally blocked by an inhibitor of RNA or protein synthesis. Many neuronal cell bodies and processes with immunoreactivity for VIP and the related peptide histidine isoleucine amide (PHI) are seen in cultured ganglia. In addition, VIP/PHI mRNA is abundant in cultured ganglia but only barely detectable in ganglia prior to culture. Under the same culture conditions, neuropeptide Y-like immunoreactivity increases to a small extent, and tyrosine hydroxylase activity and total ganglion protein remain unchanged. These results support the idea that adult sympathetic neurons exhibit plasticity in neuropeptide expression and that this plasticity, in the case of VIP, depends on changes in gene expression.Specific neurons can synthesize and release more than one neurotransmitter. For example, many adult sympathetic neurons synthesize and release both norepinephrine and neuropeptide Y (NPY), a small number synthesize and release acetylcholine and vasoactive intestinal peptide (VIP), and some use other combinations of amines and peptides (1). In addition, during-development, neurons can change the neurotransmitters they utilize. The best studied example is the ability of neonatal sympathetic neurons to start making acetylcholine and to reduce their synthesis of norepinephrine. Initially identified in cell culture, this phenomenon was subsequently shown to occur in vivo, during the development of the cholinergic sympathetic neurons that innervate the rat foot pad (2).In addition to changes in biogenic amine synthesis, the expression of colocalized neuropeptides in neonatal sympathetic neurons can also be regulated during development. Medium conditioned by cultured heart cells contains a factor that, in addition to producing a cholinergic "switch" in neonatal sympathetic neurons from the superior cervical ganglion (SCG), also increases their immunoreactivity for several peptides [i.e., VIP, substance P, somatostatin, but not NPY (3)]. Also, when sympathetic neurons innervating the foot pads in neonatal rats change from a noradrenergic to a cholinergic phenotype, they acquire immunoreactivity for VIP and calcitonin gene-related peptide (2). Finally, placing neonatal SCG in explant culture for 48 hr produces a large (50-fold) increase in the expression of substance P-like immunoreactivity (IR) (4).Much less attention has been paid to the possibility that alterations in transmitter phenotype occur in adult sympathetic neurons. With electrophysiological techniques, only a small percentage of adult sympathetic neurons were found to acquire cholinergic properties in cell culture (...

Localization, regulation and functions of neurotransmitters and neuromodulators in cervical sympathetic ganglia

“…NPY immunoreactivity and NPY mRNA in the rat SCG decrease one week after transecting the cervical sympathetic trunc (Gurusinghe et al, 1991;Hyatt-Sachs et al, 1993;Schalling et al, 1991); however, these changes were not paralleled by a decrease in the number of NPY-immunoreactive PGN (Borghini et al, 1994). After axotomy, NPY immunoreactivity is elevated in vivo (Hyatt-Sachs et al, 1993) as well as in the explanted SCG (Hyatt-Sachs et al, 1993;Zigmond et al, 1992). Interestingly, treatment of PGN with CDF/LIF, a putative "lesion factor" mainly involved in the up-regulation of galanin, VIP and substance P in axotomized neurons (see below), results in lowered NPY peptide levels with qualitative changes at the mRNA level (Nawa et al, 1991).…”

“…An increase in the number of VIP-immunoreactive cell bodies and nerve fibers is observed after axotomy of the postganglionic branches of the rat SCG (Hyatt-Sachs et al, 1993;Klimaschewski et al, 1994b;Fig. 4) as well as in ganglia maintained in organ culture (Zigmond et al, 1992). Interleukin-lp (IL-1p) has been found to potentiate this effect, while dexamethason reduces the increase in VIP immunoreactivity (Rao et al, 199313).…”

Influence of Non-Neuronal Cells on Establishment of Neuropeptide Y Expression by Sympathetic Neurons in vitro

“…The relatively immature state of sympathetic precursors may explain the difference in their response to LIF compared to postmitotic neurons. Postnatal (P0) and, to a lesser extent, adult SCG neurons downregulate NPY in response to LIF, suggesting that the NPY phenotype is stabilized over time [Zigmond et al, 1992], perhaps due to neuronal activity from preganglionic inputs [Purves and Lichtman, 1978;Rubin, 1985c]. Indeed, NPY expression is unaltered in cultures of P0 sympathetic neurons treated with the cytokines LIF or CNTF, in the presence of high KCl, which can mimic activity [Rao et al, 1992a].…”

Gene expression in peripheral arterial chemoreceptors

“…Cholinergic gene expression can be induced in sympathetic neurons exposed to conditioned media, CNTF, LIF, or retionic acid in culture (Ernsberger et al, 1989;Lewis et al, 1994;Rao et al, 1992;Berrard et al, 1993Berrard et al, , 1995. Another cholinergic trait, vasoactive intestinal peptide (VIP), can be induced in mature sympathetic ganglion by only exposing the cells to media containing fetal calf serum (Zigmond et al, 1992). Therefore, it is possible that exposing the glomus cells to fetal calf serum in culture might also induce cholinergic traits.…”