Peptides in Neuronal Function: Studies Using Frog Autonomic Ganglia

Abstract

At present, more than 20 peptides are considered as putative neurotransmitters, based primarily on their localization in nerve terminals and their actions on nerve cells (H6kfelt et al. 1980). The list is almost certainly not exhaustive and it is likely that more will be found in the future. If many peptides turn out to be neurotransmitters, one might wonder why the nervous system utilizes so many different transmitters. A detailed analysis of the action of a number of neuropeptides may reveal characteristics unique to peptidergic transmission and thus shed light on the functional significance of peptide transmitters and perhaps explain the need for multiple transmitters.Frog sympathetic ganglia and parasympathetic cardiac ganglia are excellent preparations for this purpose (Langley and Orbeli 1910; McMahan and Kuffler 1971). Structurally, they are very simple. Neurons in these ganglia are unipolar and have no dendrites. Preganglionic fibers make synaptic contacts almost exclusively on the ganglionic cell bodies. This arrangement facilitates analysis of the physiological effects of neurotransmitters and allows accurate anatomical description of synaptic connections. Analysis of possible actions of peptides in these two preparations has already revealed interesting features. In the frog sympathetic ganglia, a luteinizing hormone releasing hormone (LHRH)-Iike peptide is almost certain to be the transmitter that mediates a slow excitatory postsynaptic potential, the late slow EPSP. Certain properties of this peptidergic transmission appear to be strikingly different from those of conventional cholinergic transmission. For instance, although the LHRH-like peptide and acetylcholine (ACh) seem to be released from the same nerve terminals that form synapses of conventional morphology, the peptide can diffuse far greater distances than ACh and activate sympathetic neurons nonsynaptically. In the frog heart septum, all of the terminals on the parasympathetic neurons are positively stained by antibodies to substance P (SP). However, little or no electrical effects on those neurons have been detected that may be attributed to the SP-like immunoreactivity.Our preliminary results indicate that one target of the SP-like material may be the mast cells situated near the neurons. These results prompted us to propose a hypothesis about the general mode of actions of neuropeptides and to suggest why the nervous system uses so many different chemical messengers. METHODSBoth preparations used here, the paravertebral sympathetic ganglia and the parasympathetic ganglia of the interartrial septum of the heart, were isolated from bullfrogs (Rana catesbiana) as previously described (McMahan and Kuffler 1971;Jan and Jan 1982).Electrophysiological experiments. The isolated ganglia were pinned to a thin layer of Sylgard in a petri dish and viewed with Nomarski optics. The bath was continuously perfused at room temperature with Ringer's solution containing 115 mM NaCI, 2 mM KCI, 3.6 mM CaCI2, and 5 mM HEPES (pH 7.2). Conventional recording t...

A vasoactive intestinal peptide-like cotransmitter at cholinergic synapses between rat myenteric neurons in cell culture

“…Furthermore, in guinea pig myenteric neurons, agents that increase adenylate cyclase activity mimic the effects of VIP and agents that interfere with adenylate cyclase activity prevent responses to VIP (Palmer et al, 1987). made similar findings: single presynaptic action potentials reliably elicit postsynaptic responses caused by classical transmitters, but multiple presynaptic stimuli are required to elicit slower, peptide-mediated postsynaptic responses (Lundburg et al, 1980;Jan and Jan, 1982;Jan et al, 1983;Bishop et al, 1987;Li and Calabrese, 1987;Bartfai et al, 1988;Lundberg et al, 1989). The simplest explanation of the requirement for multiple stimuli is that single action potentials release insufficient amounts of VIP to cause detectable postsynaptic responses.…”

“…In bullfrog sympathetic ganglia, an LHRH-like peptide mediates slow synaptic excitation (Jan et al, 1979(Jan et al, , 1983Jan and Jan, 1982) and in leech heart a FMRFamide-like peptide causes increased myogenie activity (Li and Calabrese, 1987). Both of these substances are released from cholinergic neurons and have postsynaptic actions easily seen in the absence of cholinergic transmission.…”

“…Few intact neural systems lend themselves to rigorous demonstrations of cotransmission because one must be able both to identify preand postsynaptic cells reliably and to stimulate selectively only those presynaptic neuron(s) containing the hypothesized cotransmitters. The most useful preparations have been invertebrate nervous systems that contain reliably identifiable individual neurons (e.g., Adams and O'Shea, 1983;Bishop et al, 1987;Li and Calabrese, 1987) and those portions of the vertebrate peripheral nervous system that contain nearly homogeneous populations of presynaptic axons, such as visceromotor or autonomic preganglionic nerves (Jan et al, 1979(Jan et al, , 1983Lundberg et al, 1980;Jan and Jan, 1982). However, although there are several neuronal systems in which individual presynaptic axons elicit both fast and slow EPSPs (e.g., Dreyer and Chiapinelli, 1985;Brookes et al, 1988;Nusbaum and Marder, 1989) to date there is only one system, the bullfrog lumbar sympathetic ganglion, in which it has been possible to identify rigorously both a fast classical and a slow peptidergic cotransmitter at synaptic connections between neurons (Jan et al, 1979(Jan et al, , 1983Jan and Jan, 1982).…”

Potentiation of miniature endplate potential frequency by ATP in Xenopus tadpoles

“…Factors secreted by the postsynaptic cell may regulate the growth and survival of presynaptic neurones (Henderson et al, 1981;Gurney, 1984;Oppenheim & Haverkamp, 1988). It is now widely recognized that many mature neurones contain more than one neurotransmitter (Hokfelt et al, 1984), and in at least some instances, both substances have physiological effects on the postsynaptic cell (see, for example, Jan et al, 1983). Adenosine-5'-triphosphate (ATP) is known to be released in association with acetylcholine (ACh) at synapses in the vertebrate peripheral nervous system (Silinsky & Hubbard, 1973;Silinsky, 1975;Zimmerman, 1978).…”

Substance P modulation of acetylcholine-induced currents in embryonic chicken sympathetic and ciliary ganglion neurons.

“…In the ciliary ganglion, substance P-containing terminals from these preganglionic neurons contact most of the postganglionic cells (7,8). The presence of substance P in both sympathetic and parasympathetic ganglia of many species (7,8,(10)(11)(12)(13) suggests a possible physiological role for this peptide in ganglionic transmission. Furthermore, the coexistence of substance P and AcCho in preganglionic fibers raises the possibility that the role of the peptide might be to modulate AcCho action.…”