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 (...

Vasoactive intestinal peptide (VIP) increased catecholamine biosynthesis in bovine adrenal chromaffin cells by 50-200%. Six related peptides produced no effects. In addition, VIP increased tyrosine hydroxylase (TH) activity measured in gel-filtered supernatants prepared from homogenates of treated cells. The hypothesis that cyclic AMP is the second messenger involved in these effects of VIP was also evaluated. VIP led to an elevation of cyclic AMP levels, and this increase occurred over a similar concentration range and time course as the activation of TH and the increase in catecholamine biosynthesis. Each measure reached maximal levels at 10-20 microM VIP within 1 min and remained elevated for at least 16 min. These changes produced by VIP were paralleled by enhanced phosphorylation of TH, and this phosphorylation occurred on a single tryptic peptide that was the same peptide whose phosphorylation has been previously shown to be stimulated by forskolin. In contrast to VIP and forskolin, 12-O-tetradecanoylphorbol 13-acetate, a phorbol ester known to activate protein kinase C, increased the phosphorylation on a total of three tryptic peptides of TH. Our results indicate that VIP stimulates catecholamine biosynthesis in chromaffin cells through the phosphorylation and activation of TH and support the conclusion that a cyclic AMP-dependent phosphorylation of TH is responsible for these effects.

Preganglionic nerve stimulation leads to an acute elevation of tyrosine hydroxylase (TH) activity in the rat superior cervical ganglion. This effect is mediated in part by acetylcholine, acting via nicotinic receptors, and in part by a noncholinergic neurotransmitter. As a first step in an attempt to identify this noncholinergic transmitter, we have examined a number of biogenic amines, purine nucleotides, neuropeptides, and other compounds for their ability to increase TH activity. Secretin, vasoactive intestinal peptide (VIP), and PHI (a 27-amino acid peptide with an NH2-terminal histidine and a COOH-terminal isoleucine amide), all members of the secretin family of peptides, increased TH activity acutely. Human pancreatic growth hormone-releasing factor, glucagon, and gastric inhibitory peptide (three other members of this peptide family) and all other transmitter candidates tested had no effect on this enzyme activity. We have examined the possibility that this peptidergic regulation of TH activity is mediated via changes in adenosine 3',5'-cyclic monophosphate (cAMP) levels. When the six members of the secretin family were tested for their ability to increase cAMP levels in the ganglion, secretin, VIP, and PHI significantly increased this cyclic nucleotide, whereas growth hormone-releasing factor, glucagon, and gastric inhibitory peptide produced no significant effects. The rank orders of potency and of efficacy of secretin, VIP, and PHI in altering TH activity and cAMP levels were identical. Furthermore, a strong correlation was found between the cAMP level and the TH activity in individual ganglia exposed to these peptides. Finally, 8-bromoadenosine 3',5'-cyclic monophosphate and forskolin also increased TH activity.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract