Galanin-immunoreactive Neurons Research Articles

Regulation of galanin and neuropeptide Y in dorsal root ganglia and dorsal horn in rat mononeuropathic models: possible relation to tactile hypersensitivity

The expression of galanin and neuropeptide Y in rat lumbar 5 (L5) dorsal root ganglia and dorsal horn (L4–5) was studied after four types of peripheral nerve injury using immunohistochemistry and in situ hybridization. The possible correlation between these two peptides and tactile allodynia-like behaviour was analysed as well. The models employed were the Gazelius (photochemical lesion) and Seltzer and Bennett (constriction lesions) models, as well as complete sciatic nerve transection (axotomy). Two weeks after surgery, the Gazelius model rats more frequently displayed a greater tactile allodynia than the rats from the Seltzer and Bennett models. Tactile allodynia was not observed in any of the axotomized rats. A marked increase in the number of galanin-immunoreactive and galanin messenger RNA-positive neuron profiles was observed in ipsilateral dorsal root ganglia in all types of models. The increase in allodynic rats (Gazelius, Seltzer and Bennett models) was less pronounced than that after axotomy. In addition, in the Bennett model the number of galanin-immunoreactive neurons was significantly lower in allodynic rats as compared to non-allodynic rats, and the same tendency, but less obvious was found in the Seltzer model. Furthermore, an increase in galanin-immunoreactive fibres was found in the superficial laminae of the ipsilateral dorsal horn in all lesion models, especially in lamina II. A dramatic increase in the number of neuropeptide Y and neuropeptide Y messenger RNA-positive neuron profiles was also found in the ipsilateral dorsal root ganglia in all models, but no significant difference was found in peptide levels between allodynic and non-allodynic rats in any of the models. The present results suggest that the levels of endogenous galanin may play a role in whether or not allodynia develops in the Bennett model.

Galanin-containing-neurons, in the gastrointestinal tract of the lizard Podarcis s. sicula, as components of anally projecting nerve pathway

The distribution of galanin immunoreactive (Gal/IR) neurons was investigated in the gastrointestinal (GI) tract of the lizard Podarcis s. sicula. The indirect immunofluorescence method, image analysis and confocal analysis were applied to cryostat sections and whole mount preparations. Gal/IR nerve fibers and cell bodies were found throughout the lizard GI tract in the myenteric plexus, circular muscle layer and mucosa. These nerve structures decreased caudally. The stomach revealed a denser reactive nerve population than elsewhere. The projections of Gal/IR neurons were detected in the myenteric plexus of lizard gut using a confocal microscope which analyzed the immunoreactive material on the proximal and distal sides of muscle myotomies. An accumulation of Gal/IR material on the oral side of the myotomies demonstrated the oral-to-anal projection of Gal containing nerve structures. Based on our results, it can be hypothesized that Gal/IR neurons of the lizard digestive tract belong to the inhibitory descending pathway, which in most vertebrates is responsible for gut peristalsis regulation.

Galanin Modulation of Seizures and Seizure Modulation of Hippocampal Galanin in Animal Models of Status Epilepticus

We examined the role of hippocampal galanin in an animal model of status epilepticus (SE). Control rats showed abundant galanin-immunoreactive (Gal-IR) fibers in the dentate hilus, whereas no Gal-IR neurons were observed. Three hours after the onset of self-sustaining SE (SSSE), induced either by intermittent stimulation of the perforant path for 30 min (PPS) or by injection of lithium and pilocarpine, Gal-IR fibers disappeared in the hilus and remained absent for up to 1 week afterward. Twelve hours after the induction of SE by PPS or 3 hr after pilocarpine administration, Gal-IR neurons appeared in the hilus; these neurons increased in number after 1 d and gradually declined 3 and 7 d later. Galanin concentration in the hippocampus, measured by ELISA, significantly decreased on the plateau of SSSE and increased 24 hr after PPS. Galanin (0.05 nmol) injected into the hilus prevented the induction of SSSE, and 0.5 nmol of galanin stopped established SSSE. These effects were attenuated by galanin receptor antagonists (M35 > M40 >/= M15). 2-Ala-galanin (5 nmol), a putative agonist of galanin type 2 receptors, prevented but was unable to stop SSSE. M35 facilitated the development of SSSE when given before PPS. We suggest that hippocampal galanin acts as an endogenous anticonvulsant via galanin receptors. SE-induced galanin depletion in the hippocampus may contribute to the maintenance of seizure activity, whereas the increase of galanin concentration and the appearance of galanin-immunoreactive neurons may favor the cessation of SSSE. The seizure-protecting action of galanin SSSE opens new perspectives in the treatment of SE.

Presence of galanin in dopaminergic neurons of the sheep infundibular nucleus: a double staining immunohistochemical study

The distribution of tyrosine hydroxylase (TH) and of galanin immunoreactive (IR) neurons were examined in the sheep infundibular nucleus. Antisera raised against TH and galanin were used on adjacent sections and for double immunohistochemical staining of the same sections. There was considerable overlap in the distribution of TH and galanin-IR neurons in the medial part of the nucleus. Most of the galanin-IR neurons were also TH-IR, but less than 50% of the TH-IR neurons also expressed galanin immunoreactivity. Neurons immunoreactive to TH alone were observed close to the third ventricle and in the rostral part of the infundibular nucleus. In the median eminence, TH and galanin-IR fibres overlapped mainly in the lateral and dorsal parts of the external layer, but the colocalisation of both antigens could not be assessed on the available material. Thus, in sheep, the population of catecholaminergic neurons of the infundibular nucleus may be subdivided into different subpopulations according to their peptide content, but does not appear segregated as in rat and human.

Tyrosine kinase A, galanin and nitric oxide synthase within basal forebrain neurons in the rat

Cholinergic basal forebrain neurons appear to play a key role in cognition and attention. In rat, basal forebrain neurons express multiple proteins including the high-affinity signal transducing tyrosine kinase A receptor for nerve growth factor, the neuropeptide galanin and nitric oxide synthase, a marker for the novel neurotransmitter nitric oxide. The present study was undertaken to define the relationship between neurons expressing each of these markers within the medial septum-vertical limb of the diagonal band, horizontal limb of the diagonal band and nucleus basalis in colchicine pre-treated rats. Tyrosine kinase A-immunopositive neurons were seen throughout all subfields of the basal forebrain. In contrast, nitric oxide synthase- and galanin-immunoreactive neurons were mainly distributed within the septal-diagonal band complex. Co-localization experiments revealed that virtually all nitric oxide synthase-positive neurons (visualized by nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry) also contained tyrosine kinase A, whereas, many fewer tyrosine kinase A neurons were nicotinamide adenine dinucleotide phosphate-diaphorase positive within the medial septum-vertical limb of the diagonal band. Within the horizontal limb of the diagonal band, numerous nicotinamide adenine dinucleotide phosphate-diaphorase neurons expressed tyrosine kinase A, whereas only a small number of tyrosine kinase A neurons contained nicotinamide adenine dinucleotide phosphate-diaphorase. Within the nucleus basalis very few neurons were nicotinamide adenine dinucleotide phosphate-diaphorase reactive, and a minor number contained tyrosine kinase A. Additional co-localization experiments revealed minor percentages of neurons containing nicotinamide adenine dinucleotide phosphate-diaphorase and galanin immunoreactivity within the various subfields of the basal forebrain. Within the horizontal limb of the diagonal band minor numbers of nicotinamide adenine dinucleotide phosphate-diaphorase-reactive perikarya displayed galanin. Similarly, only a few galanin-containing neurons expressed nicotinamide adenine dinucleotide phosphate-diaphorase. The existence of tyrosine kinase A, nitric oxide synthase and galanin within select neuronal subgroups of the cholinergic basal forebrain suggests that these perikarya are responsive to a complex set of chemical signals. A greater understanding of the chemical signature of the cholinergic basal forebrain neurons will provide the insight required to develop novel pharmacological approaches aimed at preventing or slowing the degenerative processes that effect these neurons in aging and pathologic disorders.

Regulation of galanin in rat sympathetic neurons in vitro

The neuropeptide galanin is induced in sensory and autonomic neurons after peripheral nerve lesion. Leukemia inhibitory factor (LIF) has been suggested to be involved in the up-regulation of galanin. A direct effect of LIF on galanin content in pure sympathetic neuron cultures dissociated from newborn rat superior cervical ganglia was investigated by radioimmunoassay and immunohistochemistry. Galanin increases in sympathetic neurons during a 12 day culture period in the presence of NGF (10 ng/ml). Five days after addition of LIF (10 ng/ml) a 7-fold elevation is observed when compared to control cultures. Furthermore, galanin increases significantly in the presence of non-neuronal cells and in response to potassium-induced depolarization. The proportion of galanin-immunoreactive neurons in mixed cultures is similar to that found in adult rat superior cervical ganglia after transection of the major postganglionic branches. The results corroborate the hypothesis that LIF, presumably released from ganglionic satellite cells, induces galanin in a subpopulation of sympathetic neurons in vivo and in vitro.

Galanin-immunoreactive synaptic terminals on basal forebrain cholinergic neurons in the rat.

Previous studies have indicated that galanin is one of the most abundant peptides in the basal forebrain and that it has a significant modulatory influence on cholinergic transmission. The aim of the present study was to use a light electron microscopic correlation technique to determine whether galanin-immunoreactive terminals form synaptic contacts with basal forebrain cholinergic cells of the rat. Sections from fixed-perfused brains were stained at the light and electron microscopic levels for galanin and choline acetyltransferase immunoreactivity in the same section by using a dual-colour immunohistochemical method. The results showed that galanin-immunoreactive axonal terminals are unevenly distributed in the medial septal nucleus, the diagonal band, and the nucleus basalis. Galanin-positive synapses were most prominent on choline acetyltransferase-positive neurons in the lateral parts of the nucleus of the diagonal band and in the posterior half of the nucleus basalis, which is where there was the greatest overlap between the distribution of galanin-immunoreactive terminals and choline acetyltransferase-positive neurons. The origins of these galanin-positive terminals are not known, but the results confirm that the basal forebrain galaninergic system has a synaptic influence on basal forebrain cholinergic neurons in the rat.

Differential expression of galanin immunoreactivities in the primary sensory neurons following partial and complete sciatic nerve injuries

Neuropeptide expression in primary sensory neurons is highly plastic in response to peripheral nerve axotomy. While neuropeptide changes following complete sciatic nerve injury have been extensively studied, much less is known about the effects of partial sciatic nerve injuries on neuropeptide plasticity. Galanin, a possible endogenous analgesic peptide, was up-regulated in primary sensory neurons following complete sciatic nerve injury. We investigated the effects of partial sciatic nerve injuries on galanin expression in primary sensory neurons, and compared this effect with that after complete sciatic nerve injury. Complete transection, partial transection and chronic constriction injury were made, respectively, on the sciatic nerves of three groups of rats at high thigh level. Animals were allowed to survive for four and 14 days before being killed. L4 and L5 dorsal root ganglia, L4–5 spinal cord and lower brainstem were processed for galanin immunocytochemical staining. After all three types of sciatic nerve injuries, galanin-immunoreactive neurons were significantly increased in the ipsilateral dorsal root ganglia, and galanin-immunoreactive axonal fibres were dramatically increased in the superficial laminae of the dorsal horn and the gracile nuclei, compared to the contralateral side. However, in partial injury models, the percentages of galanin-immunoreactive dorsal root ganglion neurons were significantly higher than in complete nerve transection. Size frequency distribution analysis detected that more medium- and large-size galanin-immunoreactive dorsal root ganglion neurons were present after partial nerve transection and constriction injury than after complete nerve transection. Using a combined approach of retrograde tracing of flurorescent dyes and galanin immunostaining, we found that a partial transection increased the proportions of galanin-immunoreactive neurons among both axotomized and non-axotomized neurons. Galanin-immunoreactive axonal fibres were not only detected in the superficial laminae, but also in the deeper laminae of the dorsal horn of partial injury animals. Furthermore, more galanin-immunoreactive axonal fibres were observed in the ipsilateral gracile nuclei of partially injured rats than in completely injured rats. We conclude that partial sciatic nerve injuries induced greater galanin up-regulation in medium- and large-size dorsal root ganglion neurons than complete sciatic nerve injury. Galanin expression in primary sensory neurons seems to be differentially regulated following partial and complete sciatic nerve injuries.

Involvement of Ca oscillation in excitation of CO/H-Sensitive neurons in the VMS of rats assessed by respiratory responses

Galanin released into the hypophysial portal circulation in the hypothalamus may function as a hypophysiotropic factor regulating the anterior pituitary function or it may function as a neurotransmitter/neuromodulator acting at synaptic sites regulating neuronal activity of many neurons in the brain. Catecholamines (adrenaline, noradrenaline, and dopamine) primarily regulate anterior pituitary functions indirectly via innervating hypophysiotropic neurons. The aim of the present studies was to explore with double-label immunocytochemistry if, as in rodents, catecholamines interact with galanin in the human diencephalon. Due to the long post-mortem period and subsequent lack of optimal preservation of the cell membranes in the brain, electron microscopy could not be employed to show the presence of catecholaminergic-immunoreactive synapses on galanin-immunoreactive neurons. Therefore, we used light microscopic immunocytochemistry and high-magnification microscopy with oil immersion to identify putative juxtapositions between catecholamines and galanin-utilizing antisera against key enzymes of catecholamine synthesis (tyrosine hydroxylase (TH), representing all three catecholamines; dopamine-beta-hydroxylase (DBH), representing noradrenaline; and phenylethanolamine-N-methyltransferase (PNMT), representing adrenaline) and galanin. Our studies show that among the three catecholamines, dopamine is the most abundant and the vast majority of catecholaminergic contacts on galanin-immunoreactive neurons is dopaminergic. The number of DBH-immunoreactive contacts is less and the number of PNMT-immunopositive contacts is negligible. Among the hypothalamic regions, the periventricular region above the infundibulum (infundibular or arcuate nucleus) contained the largest number of contacts. These en passant-type intimate associations between catecholamine- and galanin-immunoreactive neuronal elements may be functional synapses and may provide the morphological basis for the catecholamine-mediated galanin release.

The structural localization of galanin, and its function in modulating acetylcholine release in the olfactory bulb of adult rat.

The localization of galanin immunoreactivity was analyzed within the olfactory bulb of adult rats. Galanin-positive neurons were differentially distributed among the bulb layers. The density of stained neurons was highest in the glomerular and external plexiform layers. According to morphology, size, location and arrangement, a large proportion of galanin-immunoreactive neurons corresponds to external tufted cells and short-axon neurons in the superficial part of the external plexiform and glomerular layers. A smaller number were middle tufted cells and short-axons neurons while only a few short-axon neurons were labeled in the granule cell layer. Galanin-stained nerve fibers had different structures (thick fibers with or without varicosities, and thin fibers with or without varicosities). Among them were afferent immunoreactive nerve fibers entering the bulb through the olfactory nerve layer, but penetrating superficial layers. Correspondingly, a large number of galanin-positive axons (with or without varicosities) were observed in the olfactory nerve layer. A number of galanin-positive nerve fibers was also present in the glomerular and internal plexiform layers, while these fibers were scarce in the granule cell layer, their density was lowest in the external plexiform layer. These results suggest that galanin-positive axons present in the olfactory bulb originate from at least four different sources. From the periphery axon bundles enter the bulb together with olfactory nerve fibers from the rostral direction and with a fiber bundle from the ventral posterior surface, i.e. at the border between the olfactory tract and the main olfactory bulb along a large blood vessel. Central sources are local interneurons in the olfactory bulb and some extrabulbar brain regions. Double-labeling experiments combining acetylcholinesterase histochemistry with galanin immunocytochemistry did not show any co-localization of acetylcholinesterase and galanin in nerve cell perikarya or nerve fibers. Synthetic porcine galanin (1-29) promoted acetylcholine release in olfactory bulb tissue slices, suggesting that galanin can effectively modulate cholinergic transmission and perhaps other forms of neuronal transmission. It is concluded that galanin may be significantly involved in olfactory processing at cellular and synaptic levels.

Target-dependent plasticity of galanin and vasoactive intestinal peptide in the rat superior cervical ganglion after nerve lesion and re-innervation.

The expression of the neuropeptides galanin and vasoactive intestinal peptide (VIP) is increased in subpopulations of sympathetic neurons after axotomy of the rat superior cervical ganglion. We investigated whether postganglionic neurons innervating different targets show a prevalence for any of the two peptides in response to carotid nerve lesion. Before the respective postganglionic axons were crushed close to the ganglion, postganglionic neurons projecting either to the iris (through the internal carotid nerve) or to the submandibular gland (through both carotid branches) were identified by the retrograde tracer Fast Blue. Galanin and VIP immunoreactivities were demonstrated two and 30 days after crush and after successful regeneration of the lesioned neurons (60 days). In control ganglia, both peptides were detected in a few gland- but not in iris-projecting neurons. However, two days after crush of the respective carotid nerves, 14% of neurons within the iris and 46% within the gland population were immunoreactive for galanin. The percentage of neurons immunoreactive for VIP was significantly lower in both populations: only 3.5% of neurons projecting to the iris and 23% of the gland-projecting neuron population exhibited this peptide. After 30 days, the percentage of galanin- and VIP-positive neurons projecting to the submandibular gland was reduced (24% and 5.7%, respectively), whereas the proportion of galanin-immunoreactive neurons further increased within the iris population (55%), indicating that some neurons express galanin at later stages after the lesion. At 60 days after the crush, the percentage of galanin- or VIP-immunoreactive neurons had decreased to control levels within those neuron populations that re-innervated the iris or submandibular gland, although the total number of neurons exhibiting galanin or VIP was still increased within the ganglion, suggesting that re-establishment of target contact may play a role in down-regulation of both peptides.

Galanin is contained in GABAergic neurons in the rat spinal dorsal horn

In order to determine which types of neuron in laminae I–III of the rat spinal dorsal horn contain the peptide galanin, pre-embedding immunocytochemistry with antiserum to galanin was combined with post-embedding detection of GABA- and glycine-like immunoreactivities. Sixty-eight galanin immunoreactive neurons in laminae I–III selected from four rats were examined, and in each case semi-thin sections through the cell body were tested with a monoclonal antibody to GABA and an antiserum to glycine. All of the 68 galanin-immunoreactive neurons tested were GABA-immunoreactive, while only one of them (in lamina III) was glycine-immunoreactive. This suggests that galanin is contained in inhibitory interneurons, and that (like enkephalin, neuropeptide Y and thyrotropin-releasing hormone) it is mainly restricted to GABAergic neurons which do not use glycine as a co-transmitter.

Ultrastructural studies on peptides in the dorsal horn of the rat spinal cord—II. Co-existence of galanin with other peptides in local neurons

Using light microscopic immunoperoxidase and immunofluorescence histochemistry, double-staining methodology, and electron microscopic pre-embedding and post-embedding immunocytochemistry, we studied galanin-immunoreactive neurons in the superficial dorsal horn of the rat spinal cord. Co-existence of galanin with other neuropeptides was also analysed. The lumbar 4 and 5 segments of normal rats and after rhizotomy or spinal cord transection were studied. Galanin-positive local neurons in lamina II were often islet cells and could be classified as type A, which had abundant electron-dense cytoplasm containing many large dense-core vesicles, and type B, which had electron-lucent cytoplasm with only a few large dense-core vesicles. Galanin-positive and -negative peripheral afferent terminals made synaptic contact mostly with galanin-negative dendrites and cell bodies, but also with type B galanin cell bodies and with galanin-positive dendrites of unidentified type. Galanin-immunoreactive terminals from local neurons could also be classified into two types. Type alpha terminals were most common; they contained densely packed synaptic vesicles and many large dense-core vesicles, were strongly immunostained and most frequently made synaptic contact with galanin-negative dendrites. Type beta terminals contained loosely packed synaptic vesicles and a few large dense-core vesicles, and were weakly immunostained. Axosomatic synaptic contact were sometimes found between type beta terminals and type B galanin-positive cell bodies, but were most often associated with galanin-negative dendrites. Double immunostaining showed that galanin-like immunoreactivity co-localized mainly with enkephalin-like, but sometimes also with neuropeptide Y-like immunoreactivity in some local neurons in lamina II. Galanin-like and substance P-like immunoreactivities were identified in the same neurons in deeper layers of the dorsal horn. Coexistence of these neuropeptides and neurotensin with galanin was demonstrated not only in terminals in lamina II but also in large dense-core vesicles, as revealed by post-embedding immunocytochemistry. These results show that galanin-immunoreactive neurons in lamina II receive inputs directly from primary afferents and frequently make synaptic contacts with other intrinsic neurons. Galanin in the superficial dorsal horn may be released both from primary afferents and local neurons to modulate sensory processing in many different ways, including interacting with enkephalin, neuropeptide Y, neurotensin and substance P released from the same and/or other local neurons.

Characterization of trout galanin and its distribution in trout brain and pituitary.

Galanin was purified from an extract of the stomach of the rainbow trout, Oncorhynchus mykiss, and its primary structure was established as Gly-Trp-Thr-Leu-Asn-Ser- Ala-Gly-Tyr-Leu10-Leu-Gly-Pro-His-Gly-Ile-Asp-Gly-His-Arg20- Thr-Leu-Ser-Asp- Lys-His-Gly-Leu-Ala. Trout galanin shows six amino acid substitutions compared with pig galanin, but the N-terminal region (residues 1-14) has been fully conserved. The distribution of galanin-immunoreactive (GAL-IR) structures in the trout brain and pituitary was studied via immunohistochemistry. GAL-IR cell bodies were observed only in the caudal telencephalon, the preoptic region, and the mediobasal hypothalamus. GAL-IR fibers, however, are widely distributed throughout the brain, with a much lower density in the midbrain and posterior brain than in the tel- and diencephalon. Particularly dense innervation of the mediobasal hypothalamus, the ventral and supracommissuralis parts of the caudal telencephalon, and the region above and below the anterior commissure was observed. A heavy innervation of the pituitary was consistently detected. GAL-IR fibers were present in neurohypophyseal digitations of both the anterior and intermediate lobes with highest density in the region of the proximal pars distalis, where growth hormone and gonadotropic cells are located. Fibers were also seen in digitations of the rostral pars distalis, in particular between the prolactin follicles. The distribution of GAL-IR neurons in the central nervous system and pituitary of the trout suggests that the peptide may exercise an important role in the regulation of neuroendocrine functions, particularly those related to reproduction.

Subpopulations of primary sensory neurons show coexistence of neuropeptides and glucocorticoid receptors in the rat spinal and trigeminal ganglia

The coexistence of the neuropeptides substance P, calcitonin gene-related peptide, galanin, somatostatin and neuropeptide Y with glucocorticoid receptors was studied in neurons of the rat lumbar dorsal root and trigeminal ganglia by means of the double immunofluorescence technique. Based on analysis of microphotographs, about one-third of the populations of nerve cells (small and large) containing substance P or calcitonin gene-related peptide immunoreactivity (IR) showed nuclear glucocorticoid receptor IR. A similar pattern was observed within the dorsal root and trigeminal ganglia. Furthermore, within the lumbar dorsal root ganglia 50% of the small neurons, containing galanin IR, possessed nuclear glucocorticoid receptor IR of moderate intensity. Glucocorticoid receptor IR was not observed in the galanin immunoreactive neurons of the trigeminal ganglion neither in the somatostatin and NPY immunoreactive neurons of both the dorsal root and the trigeminal ganglia. The results provide a chemical anatomical basis for a direct regulation by glucocorticoids of distinct populations of substance P and calcitonin gene-related peptide immunoreactive nerve cells in the lumbar spinal and trigeminal ganglia and of galanin immunoreactive nerve cells of the spinal but not of the trigeminal ganglia.

Aging impairs galanin expression in luteinizing hormone-releasing hormone neurons: effect of ovariectomy and/or estradiol treatment.

In the medial preoptic area and the diagonal band of Broca, a subset of LHRH neurons coexpresses galanin at a 4- to 5-fold higher rate in female than male rats, suggesting that estradiol (E2) plays a key role in galanin gene expression within LHRH neurons. In the present studies we investigated the incidence of colocalization of these peptides in different age groups, i.e. 2-, 10-, 18-, and 24-month-old intact female Fisher rats; 24-month-old E2-treated rats; 24-month-old ovariectomized (OVX) rats; and 24-month-old OVX E2-treated rats with single or double labeling immunocytochemistry. For cell counting, we took advantage of the typical fusiform morphology of galanin-immunoreactive neurons that colocalize LHRH. The presence of both peptides in the same perikaryon was substantiated by double staining representative sections from each brain. Our observations indicate that the number of galanin/LHRH-coexpressing perikarya dramatically decreased with age. Although in 18-month-old rats a moderate decline was observed, in 24-month-old female rats no, or only a few, faintly stained, fusiform galanin-immunopositive perikarya were present. Although galanin was absent from LHRH neurons of aged rats, their LHRH content was not altered. E2 treatment of intact 24-month-old rats had no effect on the low incidence of colocalization. However, when OVX 24-month-old rats were E2 treated, the incidence of colocalization increased to the level seen in 2- or 10-month-old estrous animals. Our observations on the presence of colocalizing perikarya in intact and E2-treated aged animals provide further evidence for the key role of E2 in galanin gene expression within LHRH neurons and emphasize that some ovarian factor(s) may blunt this effect.

Immunocytochemical Localization of Progesterone Receptors in Galanin Neurons in the Guinea Pig Hypothalamus

A double-label immunocytochemical technique was used to determine whether progesterone receptor-containing neurons in the female guinea-pig hypothalamus also contained galanin. Adult ovariectomized guinea-pigs were primed by estradiol to induce progesterone receptors and injected intracerebroventricularly with colchicine to visualize galanin-immunopositive neurons. A small proportion of progesterone receptor-containing perikarya in the medial preoptic area and the mediobasal hypothalamus were bound to be immunoreactive for galanin. The medial preoptic, periventricular and arcuate nuclei showed the greatest concentration of double-labelled cells. Galanin varicosities appeared in close proximity to neurons with progesterone receptor-containing nuclei. These results provide neuroanatomical evidence that a subset of hypothalamic galanin-immunoreactive neurons is directly regulated by progesterone.

Distribution, origin and plasticity of galanin-immunoreactivity in the rat carotid body

The distribution, origin and plasticity of galanin immunoreactivity in the rat carotid body was examined using an indirect immunofluorescence method. Galanin-immunoreactive nerve fibers were observed around the blood vessels as well as around the clusters of glomus and sustentacular cells. A double-immunofluorescence method revealed the coexistence of galanin- and calcitonin gene-related peptide-immunoreactivities in these nerve fibers. In the jugular, petrosal and nodose ganglia which supply the sensory nerve fibers to the carotid body, subpopulations of neurons showed both galanin- and calcitonin gene-related peptide-immunoreactivities. In the superior cervical ganglion, a few neurons were immunoreactive for galanin but not calcitonin gene-related peptide. While the nerve fibers showing both galanin- and calcitonin gene-related peptide-immunoreactivities disappeared after transection of the carotid sinus nerve, many galanin-immunoreactive nerve fibers without calcitonin gene-related peptide-immunoreactivity appeared throughout the operated carotid body. In addition, galanin-immunoreactive glomus cells which were not observed in the normal carotid body, were apparent at one and three days after transection of the carotid sinus nerve. At seven days after the carotid sinus nerve transection, the galanin-immunoreactive glomus cells disappeared. In the superior cervical ganglion, the number of galanin-immunoreactive neurons increased from one day after transection of the carotid sinus nerve. Within three days after the carotid sinus nerve transection in combination with superior cervical ganglionectomy, all galanin-immunoreactive nerve fibers disappeared, while many galanin-immunoreactive glomus cells appeared in the operated carotid body. At seven days after this operation, the number of galanin-immunoreactive glomus cells decreased and a few galanin-immunoreactive nerve fibers with or without calcitonin gene-related peptide-immunoreactivities appeared. Transection of the vagus nerve had no effect on the number or distribution of galanin-immunoreactivity in the carotid body. Disappearance of galanin- and calcitonin gene-related peptide-immunoreactive nerve fibers after transection of the carotid sinus nerve suggests that the majority of those nerve fibers originate from petrosal neurons which colocalize galanin- and calcitonin gene-related peptide-immunoreactivity. In addition, the carotid sinus nerve transection may cause the acquisition of galanin-immunoreactivity in originally immunonegative glomus cells, and in nerve fibers which probably originate from the superior cervical ganglion.

The proportion of galanin-immunoreactive neurons in mouse trigeminal ganglia is transiently increased following corneal inoculation of herpes simplex virus type-1.

To investigate whether neurobiological functions are modified by viral infection, we inoculated mouse corneas with herpes simplex virus type 1 (HSV-1) and examined neuronal galanin content in trigeminal ganglia at selected survival times. HSV-1 antigen appeared in neurons at day 3, peaked at day 6 and disappeared by day 11. Increased galanin positivity was first seen at day 6, peaked at day 10 and approached control values by day 21. This result provides further evidence that the biological program of peripheral sensory neurons is modified by herpes-virus infection.

Galanin immunoreactivity in the primate central nervous system.

Galanin-immunoreactive profiles were localized within the monkey and human central nervous system. In the monkey telencephalon, galanin-immunoreactive perikarya were seen within the anterior olfactory nucleus, basal forebrain, endopiriform nucleus, hippocampus, and bed nucleus of the stria terminalis. The caudate nucleus and putamen contained galanin-immunoreactive perikarya whereas the nucleus accumbens displayed only galanin-immunoreactive fibers. In the diencephalon, galanin-immunoreactive profiles were seen within the medial preoptic area, periventricular, suprachiasmatic, paraventricular, and arcuate nuclei as well as the lateral hypothalamic area. Within the thalamus, only galanin-immunoreactive fibers were seen within the midline paraventricular, reuniens, and rhomboid nuclei. In the mesencephalon, scattered galanin-immunoreactive fibers were seen in the periaquaductal gray, ventral tegmental area, and midbrain reticular formation. In the metencephalon, galanin-immunoreactive neurons were observed in the medial vestibular nucleus and nucleus prepositus. In the myelencephalon, galanin-immunoreactive perikarya were seen within the nucleus of the tractus solitarius and hypoglossal nucleus. Dense collections of galanin-immunoreactive fibers were found in the spinal descending tract of V, nucleus of the tractus solitarius, and dorsal motor nucleus of X. Galanin immunoreactivity was also observed within all circumventricular organs. Spinal anterior horn neurons expressed galanin immunoreactivity, and immunopositive fibers were seen within the tract of Lissauer and the substantia gelatinosa. Although the distribution of galanin immunoreactivity was generally similar between monkeys and humans, there were a few striking exceptions. The human supraoptic nucleus contained galanin-immunoreactive neurons, whereas the monkey supraoptic nucleus displayed only immunopositive fibers. Similarly, galanin-immunoreactive perikarya and fibers were seen in the human locus coeruleus and subcoeruleus, whereas in monkeys these regions contained only fibers. These data demonstrate a widespread distribution of galanin-containing profiles in primates, suggesting that galanin may modulate cognitive, sensory, motor, and autonomic processes.