T. Melander

Coexistence of galanin-like immunoreactivity with catecholamines, 5- hydroxytryptamine, GABA and neuropeptides in the rat CNS

The coexistence of galanin (GAL)-like immunoreactivity (LI) with markers for catecholamines, 5-hydroxytryptamine (5-HT), GABA, or some neuropeptides was mapped in the rat CNS by using adjacent sections, as well as by elution-restaining and double-labeling immunocytochemistry. Many instances of coexistence were observed, but there were also numerous GAL-positive cell body populations displaying distributions similar to those of these markers but without apparent coexistence. In the hypothalamic arcuate nucleus GAL-LI was found in a large proportion of tyrosine hydroxylase (TH)-positive cell bodies (A12 cells), both in the dorsomedial and ventrolateral subdivisions, with a higher number in the latter. GAL-LI coexisted in glutamic acid decarboxylase (GAD)- positive somata in the posterior aspects of the arcuate nucleus and at all rostrocaudal levels in fibers in the external layer of the median eminence. In the anterior hypothalamus, a large population of the cells of the parvocellular and magnocellular paraventricular nuclei contained both GAL-LI and vasopressin-LI. Moreover, somata containing both GAD- and GAL-LI were seen lateral to the mammillary recess in the tuberal and caudal magnocellular nuclei. Some of the neurons of the caudal group were shown to project to the occipital cortex using combined retrograde tracing and immunofluorescence. With regard to mesencephalic and medullary catecholamine neurons, GAL-LI coexisted in a large proportion of the noradrenergic locus coeruleus somata (A6 cell group) and in the A4 group dorsolateral to the fourth ventricle, as well as in the caudal parts of the A2 group in the dorsal vagal complex. However, in more rostral parts of the latter, especially in the medial subdivision of the solitary tract nucleus, a very large population of GAL-IR small cell bodies was seen intermingling with catecholamine neurons, but they did not contain TH-LI. Furthermore, GAL-IR cell bodies coextensive with, but not coexisting in, TH-IR somata were seen in the C1 (epinephrine) horea in the ventrolateral medulla at the level of area postrema and in the most rostral aspects of the C1 group. Finally, 5-HT-positive cell bodies of the mesencephalic and medullary raphe nuclei and a subpopulation of coarse 5-HT nerve fibers in the hippocampus co-contained GAL-LI. The present results demonstrate that a GAL-like peptide is present in many systems containing other neuroactive compounds, including dopamine, norepinephrine, 5-HT, GABA, and vasopressin.(ABSTRACT TRUNCATED AT 400 WORDS)

Increase of galanin-like immunoreactivity in rat dorsal root ganglion cells after peripheral axotomy

The L4 and L5 dorsal root ganglia were studied in untreated rats and rats subjected to unilateral transection of the sciatic nerve, using the indirect immunofluorescence technique and antibodies to the peptide galanin (GAL). In control rats only low numbers of small ganglion cells contained GAL-like immunoreactivity (LI). After axotomy a marked increase in the number and intensity of GAL-immunoreactive ganglion cell bodies was seen on the lesion side. Thus, some primary sensory neurons react to transection of their peripheral branches by expressing increased GAL levels. A similar reaction has been described by other groups for vasoactive intestinal polypeptide.

A galanin-like peptide in the central nervous system and intestine of the rat

Galanin (GAL), a 29 amino acid peptide, was recently isolated from the small intestine of pigs. In the present study an antiserum towards porcine GAL has been developed and used for radioimmunoassay and immunohistochemical studies. We now report that GAL-like immunoreactivity occurs in wide-spread systems in the rat CNS and intestine.

Coexistence of peptides with classical neurotransmitters

In the present article the fact is emphasized that neuropeptides often are located in the same neurons as classical transmitters such as acetylcholine, 5-hydroxy-tryptamine, catecholamines, γ-aminobutyric acid (GABA) etc. This raises the possibility that neurons produce, store and release more than the one messenger molecule. The exact functional role of such coesisting peptides is often difficult to evaluate, especially in the central nervous system. In the periphery some studies indicate apparently meaningful interactions of different types with the classical transmitter, but other types of actions including trophic effects have been observed. More recently it has been shown that some neurons contain more than one classical transmitter, e.g. 5-HT plus GABA, further underlining the view that transfer of information across synapses may be more compex than perhaps hitherto assumed.

Galanin-like immunoreactivity in cholinergic neurons of the septum-basal forebrain complex projecting to the hippocampus of the rat

It is now well recognized that there are several groups of cholinergic neurons in the basal forebrain with direct projections to various cortical regions. Immunohistochemical investigations of the distribution of the neuropeptide galanin (GAL) have shown that two of these brain areas, the medial septum and diagonal band, contained large numbers of GAL-immunoreactive neurons. In the present study, double staining techniques using antibodies raised against choline acetyltransferase (ChAT) revealed that GAL- and ChAT-like immunoreactivities are colocalized within a subpopulation of the cholinergic neurons within the medial septum and diagonal band. This colocalization of GAL- and ChAT-immunoreactivities was not seen to occur within other groups of forebrain cholinergic neurons. Immunohistochemistry carried out subsequent to injections of fluorescent retrograde tracers into the hippocampal formation revealed that both ChAT/GAL- and ChAT-containing neurons project to the hippocampal formation. The question of GAL as a modulator of cholinergic transmission in this projection is discussed.

Distribution of galanin-like immunoreactivity in the gastro-intestinal tract of several mammalian species.

SummaryThe distribution of galanin-immunoreactive (GAL-IR) neurons was mapped in detail in the gastro-intestinal tract of the rat, mouse, guinea-pig and pig by use of the indirect immunofluorescence technique. GAL-IR cell bodies were found in both the submucous and the myenteric plexus, with considerably higher numbers in the former ganglia. The largest number of GAL-IR perikarya was seen in the duodenal submucous plexus of the pig. With some (single) exceptions, GAL-IR cell somata were not observed in the myenteric plexus of the pig and guinea-pig, and in the submucous plexus of the esophagus and the stomach of the guinea-pig.GAL-IR fibers ocurred in most parts of the gastro-intestinal tract. In the lamina propria a few non-varicose, weakly fluorescent fibers were noted in the mouse and rat, whereas in the pig and guinea-pig were large numbers of GAL-IR fibers with a varicose appearance was observed. These fibers were in all species most numerous in the distal portion of the intestinal tract. In the submucosa GAL-IR fibers were detected in all four species, and in the pig and guinea-pig some fibers surrounded blood vessels. A large number of GAL-IR fibers was generally seen in the circular smooth muscle layer, except in the guinea-pig, which only seemed to contain a few fibers. In the longitudinal muscle layer only single fibers could be detected. However, the gastric fundus region of the pig contained a moderate number of fibers in the longitudinally and obliquely oriented layers.In general, in the rat, mouse and pig, the submucous and myenteric plexus contained moderate or large numbers of GAL-IR fibers. In the guinea-pig, no or only single fibers were observed in the plexus of the upper gastro-intestinal tract and the rectum, while moderate numbers were seen in the ileum and colon.Thin adjacent sections stained for vasoactive intestinal polypeptide (VIP) and GAL revealed the coexistence of these two peptides in cell bodies of the myenteric plexus in the pig duodenum and guinea-pig colon. In these two species the GALand VIP-nerve fiber networks also exhibited marked similarities. However, in the rat and mouse VIPand GAL-distribution patterns were in general different.The present findings indicate the presence of yet another neuropeptide or peptide family in the gastro-intestinal tract of several rodents and the pig.

The hypothalamic arcuate nucleus-median eminence complex: Immunohistochemistry of transmitters, peptides and DARPP-32 with special reference to coexistence in dopamine neurons

In this paper, we describe the results of a series of experiments which have examined the distribution within the arcuate nucleus of the hypothalamus of neurons containing the following immunoreactivities: TH-LI, GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-LI, Leu-ENK-LI, Met-ENK-7-LI, Met-ENK-8-LI, metorphamide-LI, DYN-LI, NPY-LI, SOM-LI, FMRFamide-LI, and CLIP-LI and ependymal tanycytes containing DARPP-32-LI. Using elution-restaining and double antibody staining techniques we have established numerous patterns of coexistence of these various neurotransmitters and neuropeptides. Thus, neurons containing TH-LI were, in some instances, also found to contain GAD-LI, NT-LI, GAL-LI, GRF-LI, Met-ENK-8-LI, Leu-ENK-LI, or DYN-LI or combinations of these compounds. For example, some TH-IR neurons also contained GAL-LI and GRF-LI, while other TH-IR. neurons were also seen to contain GRF- and NT-LI. These neurons may, in fact, contain even more compounds. NPY-IR neurons and those containing SOM-LI and CLIP-LI were distinct and separate from those containing TH-LI. The distribution of these different neurochemical types of neurons and their patterns of coexistence are summarized in Fig. 34, while the relative distribution patterns of immunoreactive fibres in the median eminence are summarized in Fig. 35.

Chapter 4 Coexistence of neuronal messengers — an overview

Publisher Summary This chapter discusses results demonstrating that neurons often contain more than one chemical compound. The different types of coexistence situations are described, including (1) a classical transmitter and one or more peptides, (2) more than one classical transmitter, and (3) a classical transmitter, a peptide, and adenosine triphosphate (ATP). The functional significance of these histochemical findings is at present difficult to evaluate, but in studies on the peripheral nervous system evidence has been obtained that classical transmitter and peptide are coreleased and interact in a cooperative way on effector cells. In addition to enhancement, there is evidence that other types of interactions may occur—for example, the peptide may inhibit the release of the classical transmitter. Also in the central nervous system (CNS), indirect evidence is present for similar mechanisms—that is, to strengthen transmission at synaptic (or non-synaptic) sites and for the peptide inhibition of release of a classical transmitter. Multiple messengers may provide the means for increasing the capacity for information transfer in the nervous system.

Evidence for an inhibitory effect of the peptide galanin on dopamine release from the rat median eminence.

The role of the neuropeptide galanin (GAL) in rat hypothalamus has been studied in different experimental models. Thus, the effect of GAL on potassium-induced dopamine release was analyzed in vitro, and the localization of GAL and GAL binding sites was studied with immunohistochemistry and receptor autoradiography, respectively. In the median eminence GAL and presumably dopamine were found to coexist in nerve endings and this area contained a high density of 125I-GAL binding sites. In vitro experiments revealed that GAL inhibited the release of [3H]dopamine in a dose-dependent manner (IC50 = 7-10 nM), possibly via a presynaptic receptor.

Immunohistochemical evidence for a spinothalamic pathway co-containing cholecystokinin- and galanin-like immunoreactivities in the rat.

Using indirect immunofluorescence technique combined with retrograde tracing as well as surgical lesions, a system of spinothalamic neurons containing both galanin- and cholecystokinin-like immunoreactivity has been defined. The cell bodies are located in the lumbar segments L1-L5 with a preferential localization dorsal to the central canal at rostral levels and lateral to the canal at caudal levels. The cells project via the ventral part of the lateral funiculus to the most ventral and posterior parts of thalamus. Here a distinct, varicose terminal network was seen extending caudally from an area lateral to the medial lemniscus, running medially over the medial lemniscus, traversing the parafascicular nucleus and running dorsal to the fasciculus retroflexus into the periventricular gray matter. Transection of various parts of the spinal cord as well as retrograde tracing experiments indicate that the spinothalamic galanin cholecystokinin system represents a crossed pathway. The present results demonstrate that a spinothalamic system can be characterized by its content of galanin- and cholecystokinin-like peptides, two putative messenger molecules. It is only a minor component of the total spinothalamic projection.