Galanin-like immunoreactivity in capsaicin sensitive sensory neurons and ganglia

Ultrastructural studies on peptides in the dorsal horn of the spinal cord--I. Co-existence of galanin with other peptides in primary afferents in normal rats

The aim of the present study was to investigate galanin-like immunoreactivity in primary afferent terminals and its relationship to other neuropeptides in laminae I and II of the fourth and fifth lumbar segments of normal rat spinal cord using immunofluorescence and pre- and post-embedding electron-microscopic immunocytochemistry. Triple-immunofluorescence staining showed that galanin-like immunoreactivity co-localized with substance P- and calcitonin gene-related peptide-like immunoreactivities in many nerve fibres and terminals in laminae I and II of the dorsal horn. At the ultrastructural level, using pre-embedding immunocytochemistry, galanin-like immunoreactivity was found in type I glomeruli with an electron-dense central terminal containing many densely packed synaptic vesicles and several large dense-core vesicles. Both the cytoplasm and the core of the large vesicles were immunoreactive. In type II glomeruli with an electron-lucent central terminal and loosely packed synaptic vesicles the large dense-core vesicles and the cytoplasm were only weakly galanin-positive. Post-embedding immunocytochemistry revealed that galanin-like immunoreactivity co-existed with substance P- and calcitonin gene-related peptide-like immunoreactivities in many terminals and in individual large dense-core vesicles in lamina II. These terminals were considered to represent primary afferents, since there is evidence that calcitonin gene-related peptide in the dorsal horn only occurs in nerve endings originating in dorsal root ganglia. Evidence was also unexpectedly obtained for the occurrence of several other peptides in calcitonin gene-related peptide-positive terminals, i.e. in presumably primary afferents. Thus galanin-like immunoreactivity sometimes also co-localized with cholecystokinin- and neuropeptide tyrosine-like immunoreactivities in calcitonin gene-related peptide-immunoreactive terminals and in some large dense-core vesicles in such terminals. A small number of calcitonin gene-related peptide immunoreactive, presumably primary afferent terminals contained enkephalin-, neurotensin- (and galanin-)like immunoreactivities. These results indicated that galanin can be co-stored with several other neuropeptides in large dense-core vesicles in primary afferent terminals and may presumably be released together with them in the superficial layer of the dorsal horn. Since various combinations of peptides, presumably at varying concentrations, occur in the large dense-core vesicles in a given nerve ending, it is likely that the individual large dense-core vesicles produced in a neuron are heterogenous with regard to peptide content and thus to the message that they transmit upon release.

Large calibre primary afferent neurons projecting to the gracile nucleus express neuropeptide Y after sciatic nerve lesions: an immunohistochemical and in situ hybridization study in rats

Using immunohistochemistry and in situ hybridization, we studied changes in expression of some neuropeptides in large and medium-sized neurons in lumbar 4 and 5 rat dorsal root ganglia projecting to the gracile nucleus, in response to peripheral axotomy. Fourteen days after unilateral sciatic nerve transection, many large neurons and some medium-sized neurons in ipsilateral dorsal root ganglia were strongly neuropeptide Y-positive. Galanin-, vasoactive intestinal polypeptide (VIP)- and peptide histidine-isoleucine (PHI)-like immunoreactivities coexisted with neuropeptide Y-like immunoreactivity in some of these neurons. After axotomy numerous large and medium-sized cells contained neuropeptide Y mRNA in the ipsilateral ganglia, whereas no hybridization was seen in the contralateral or control ganglia. Cross-sectioned, large neuropeptide Y-positive fibres were observed in a somatotopically appropriate zone within the ipsilateral gracile fasciculus. A dense network of neuropeptide Y-immunoreactive, large nerve fibres and terminals was seen in the ipsilateral gracile nucleus. A small number of galanin- and VIP/PHI-like immunoreactive nerve fibres and terminals were also observed in adjacent sections. Neuropeptide Y-like immunoreactivity colocalized with galanin- or VIP/PHI-like immunoreactivity in some nerve fibres. None of these neuropeptide immunoreactivities could be detected in nerve fibres and terminals in the control or contralateral gracile nucleus. These findings suggest that neuropeptides, in addition to their role in small dorsal root ganglion neurons, may have a function in large and medium-sized dorsal root ganglion neurons projecting to laminae III and IV in the dorsal horn as well as to the gracile nuclei, as a part of their response to peripheral axotomy.

Deafferentation-induced changes in neuropeptides of the adult rat dorsal horn following pronase injection of the sciatic nerve

The effect of deafferentation on the neuropeptides substance P (SP), calcitonin gene-related peptide (CGRP), somatostatin (SS), and cholecystokinin (CCK) in the lumbar dorsal horn of the adult rat was examined by the indirect immunohistochemical method. Deafferentation was induced by injecting the sciatic nerve of anesthetized rats with proteolytic enzymes (20 mg pronase), which cause selective death of the nerve's ganglion cells and degeneration of their terminal arborization in the spinal cord. The density of immunolabel of each peptide was determined by using a computerized densitometry analysis system in two animal groups, i.e., short-term (10-13 days after injection) and long-term (4-9 months). In both groups, the deafferentation produced a significant ipsilateral depletion of CGRP, SP, CCK, and SS immunoreactivity. This depletion was limited to the area occupied by the sciatic terminals in the dorsal horn. In the long-term group, the loss of CGRP and SP staining was significantly less than that in the short-term animals, thus indicating partial recovery. A similar, but not statistically significant, trend was observed for CCK and SS. The large decrease in CGRP and SP seen in short-term animals reflects the large contribution of the sciatic nerve to the lumbar dorsal horn. The partial recovery of peptides demonstrates the plasticity of the nervous system and may parallel sprouting of primary afferents from other nerves, such as the saphenous nerve, as we have demonstrated in previous studies.

Galanin immunoreactivity in rat spinal lamina IX: emphasis on sexually dimorphic regions

Fibers and puncta that contained galanin-like immunoreactivity (GAL-LI) were distributed within lamina IX in a heterogeneous fashion. In cervical spinal segments, GAL-LI was almost absent except for the phrenic nucleus, which received the most robust GAL-LI innervation in lamina IX. In high and mid-thoracic segments, GAL-LI was found in moderate amounts, but the number of GAL-LI fibers gradually diminished in a caudal fashion, so that in low thoracic segments GAL-LI was sparse. Throughout all thoracic segments, GAL-LI fibers surrounded some clusters of motoneurons, while other groups of motoneurons were devoid of GAL-LI fibers. In lumbar segments, three sexually dimorphic nuclei received sparse to moderate amounts of GAL-LI, while GAL-LI in the remainder of lumbar lamina IX was very sparse. In sacral spinal segments, GAL-LI was very sparse. These data indicate that fibers and puncta that contain GAL-LI preferentially surround motoneurons that innervate muscles associated with the axial skeleton, while motoneurons that innervate appendicular or tail-associated skeletal muscles only have an occasional GAL-LI fiber associated with them.

Appearance of neuropeptide Y-like immunoreactive cells in the rat trigeminal ganglion following dental injuries

The effects of these injuries on the presence and distribution of neuropeptide Y (NPY)-immunoreactive (-IR) neurones were examined immunohistochemically. In the normal trigeminal ganglion: some perivascular nerves displayed NPY-IR but there were no NPY-IR ganglionic cells. Fourteen days after extraction or pulp exposure of the upper first molar, NPY-IR cells appeared in the maxillary region of the trigeminal ganglion. About 90% of the injury-evoked NPY-IR cells had medium to large diameters (more than 300 microns2 in cross-sectional area). Shallow cavity preparation, however, did not induce the appearance of NPY-IR cells in the trigeminal ganglion. These results indicate the dental injuries alter the primary sensory neurones in the trigeminal ganglion.

Silent ischemia: a hypothetical mechanism

Ischemia of visceral organs, especially the heart, is often a painful and potentially life-threatening condition. However, in at least 75% of all cases myocardial ischemia may be "silent" (i.e., without pain or sensation). Yet, the mechanisms responsible for silent ischemia are not well understood. As such, many different theories have been advanced to explain silent ischemia; however, none have been able to adequately explain all of the experimental and clinical findings. This paper proposes a hypothetical mechanism that may help to understand mechanisms of silent ischemia.

Effect of peripheral nerve cut on neuropeptides in dorsal root ganglia and the spinal cord of monkey with special reference to galanin

Using the indirect immunofluorescence method and in situ hybridization, the localization and levels of immunoreactivities and mRNAs for several neuropeptides were studied in lumbar dorsal root ganglia and spinal cord of untreated monkeys (Macaca mulatta) and after unilateral transection of the sciatic nerve. Immunoreactive galanin, calcitonin gene-related peptide, substance P and somatostatin and their mRNAs were found in cell bodies in dorsal root ganglia of untreated monkeys and on the contralateral side of the monkeys with unilateral sciatic nerve lesion. After axotomy there was a marked decrease in the number of calcitonin gene-related peptide-, substance P- and somatostatin-positive neurons in dorsal root ganglia ipsilateral to the lesion, whereas the number of galanin positive cells strongly increased. A few neuropeptide tyrosine-positive cells were seen in after axotomy, whereas no such neurons were found in controls. No vasoactive intestinal polypeptide-, peptide histidine isoleucine-, cholecystokinin-, dynorphin-, enkephalin-, neurotensin- or thyrotrophin releasing hormone-positive cell bodies were seen in dorsal root ganglia of any of the groups studied. In the dorsal horn of the spinal cord all peptide immunoreactivities described above, except thyrotropin releasing hormone, were found in varying numbers of nerve fibres with a similar distribution in untreated monkeys and in the contralateral dorsal horn in monkey with unilateral sciatic nerve lesion. Two cholecystokinin antisera were used directed against the C- and N-terminal portions, respectively, showing a distinctly different distribution pattern in the dorsal horn. Somatostatin- and dynorphin-like immunoreactivities were also observed in small neurons in the dorsal horn. No certain effect of axotomy on these interneurons could be seen. However, marked changes were observed after this type of lesion for some peptide containing fibres in the ipsilateral dorsal horn. Thus, there was a marked increase in galanin-like immunoreactivity, whereas calcitonin gene-related peptide-, substance P-, somatostatin-, peptide histidine isoleucine neurotensin- and cholecystokinin-like immunoreactivities decreased. No changes could be observed in neuropeptide tyrosine or enkephalin-positive fibres. The present results demonstrate marked ganglionic and transganglionic changes in peptide levels after peripheral axotomy. When compared to published results on the effect of axotomy on peptides in dorsal root ganglia and spinal cord of rat, both similarities and differences were encountered.(ABSTRACT TRUNCATED AT 400 WORDS)

Oxytocin modulates the effects of galanin in carrageenan-induced hyperalgesia in rats

In the present study we have investigated the effects of galanin and/or oxytocin on carrageenan-induced hyperalgesia, the relationship between oxytocin and galanin-containing nerve fibers in the spinal cord and the influence of galanin on oxytocin secretion. Galanin (1 microgram) given intrathecally (i.t.) decreased significantly the mechanical nociceptive threshold of the carrageenan-treated hindpaw, with no significant effect on thermal nociception. The decrease in the mechanonociceptive threshold exerted by galanin was modulated by oxytocin (1 microgram, i.t.) administered simultaneously. There was a close relationship between galanin- and oxytocin-immunoreactive fibers in the dorsal horn of the thoracic spinal cord, although there was no evidence for colocalization. Galanin 0.1 and 1 microgram given intracerebroventricularly or intraperitoneally significantly decreased the oxytocin level in plasma 60 min after injection. Taken together, these data indicate that galanin may contribute to mechanical hyperalgesia by inhibiting the release of oxytocin from nerve terminals in the spinal cord and that oxytocin may be a potential analgesic agent.

Trigeminal nuclear complex of the ferret: anatomical and immunohistochemical studies

In order to establish the ferret as an animal model for studies of trigeminal pain, we describe the cytoarchitecture and neurochemistry of the trigeminal nuclear complex in the ferret and compare them to those of the cat and rat. The complex was divided as previously described, but the ferret differed in the extent of the nuclear boundaries. The neuroanatomical istribution of substance P-, calcitonin gene-related peptide-, galanin-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and neurotensin-immunoreactivity was determined throughout the rostrocaudal extent of the complex. In subnucleus caudalis, substance P-, calcitonin gene-related peptide-, enkephalin-, serotonin-, somatostatin-, neuropeptide Y-, and galanin-immunoreactivity was densest in laminae I and II. In subnucleus interpolaris, immunoreactivity for all the above neurochemicals was most dense along the lateral border and the ventral third of the caudal part of the subnucleus. Enkephalin-immunoreactive cell bodies were present in subnucleus caudalis and interpolaris. In subnucleus oralis, labelling for substance P, calcitonin gene-related peptide, galanin, enkephalin, and serotonin was most prominent in the dorsomedial part of the subnucleus. Somatostatin-immunoreactive cell bodies were distributed throughout the spinal nucleus. Labelling of serotonin, substance P, calcitonin gene-related peptide, galanin, enkephalin, and somatostatin was present in the main sensory nucleus. The motor nucleus contained fibers immunoreactive for substance P, enkephalin, serotonin and neuropeptide Y, and cell bodies immunoreactive for calcitonin gene-related peptide. The majority of neurotensin-immunoreactivity was found at the level of subnucleus caudalis, where it was densest in the trigeminal extension of the lateral cervical nucleus. The distribution of peptides in this species throughout the spinal nucleus is consistent with the notion that all the subnuclei may be involved in the processing of nociceptive inputs.

Evidence for endogenous inhibition of autotomy by galanin in the rat after sciatic nerve section: demonstrated by chronic intrathecal infusion of a high affinity galanin receptor antagonist

We have studied the effect of M-35 [Galanin(1-12)-Pro-bradykinin(2-9)-amide], a newly developed high affinity antagonist for galanin receptors, on self-mutilation (autotomy) behavior of the deafferented limb in rats after unilateral section of sciatic nerves. M-35 (1.3 micrograms/microliters) or saline was applied to the lumbar spinal cord through a chronically implanted intrathecal catheter at a rate of 0.5 microliter/h for 10 days post axotomy via an osmotic minipump. Axotomized rats infused with M-35 autotomized significantly more than those perfused intrathecally with saline or those axotomized rats not implanted with an intrathecal catheter. The severity of autotomy was also markedly greater in the group treated with M-35 than in the two other groups. M-35 did not noticeably influence either the galanin mRNA level in corresponding dorsal root ganglia and dorsal horn region or the percent of lumbar sensory neurons expressing detectable levels of mRNA for galanin. It is suggested that galanin can endogenously suppress autotomy behavior in rats after nerve injury and thus may play an important role in the control of the development of neuropathic pain.

Emerging relationships between cytochemical properties and sensory modality transmission in primary sensory neurons

Primary sensory neurons have been categorized according to a variety of characteristics, including modality responsiveness, somal size, cytology, cytochemistry, and the organization of their central axon collateral arborizations. A major aim in the study of primary afferents has been to determine the relationships between dorsal root ganglia neuronal physiology, anatomy, and chemistry that could provide a basis for a classification scheme more directly relevant to function. Here we briefly review these relationships and examine the utility of specific histochemical and immunohistochemical markers representative of distinct populations of neurons that may transmit particular sensory modalities. In addition, we discuss some of our observations suggesting that one population of dorsal root ganglia neurons contains high levels of cytochrome oxidase, carbonic anhydrase, parvalbumin, and calbindin D28k, while a separate population contains fluoride-resistant acid phosphatase, calcitonin gene-related peptide, and displays immunoreactivity with an antibody that labels the central arborization of a specific class of unmyelinated afferents in the dorsal horn. This may have implications for the combinations of substances contained within neurons with distinct sensory functions.

Fine structural aspects of secretion and extrinsic innervation in the olfactory mucosa

The mucus at the surface of the olfactory mucosa constitutes the milieu in which perireceptor events associated with olfactory transduction occur. In this review, the ultrastructure of olfactory mucus and of the secretory cells that synthesize and secrete olfactory mucus in the vertebrate olfactory mucosa is described. Bowman's glands are present in the olfactory mucosa of all vertebrates except fish. They consist of acini, which may contain mucous or serous cells or both, and ducts that traverse the olfactory epithelium to deliver secretions to the epithelial surface. Sustentacular cells are present in the olfactory epithelium of all vertebrates. In fish, amphibia, reptiles, and birds, they are secretory; in mammals, they generally are considered to be "non-secretory," although they may participate in the regulation of the mucous composition through micropinocytotic secretion and uptake. Goblet cells occur in the olfactory epithelium of fish and secrete a mucous product. Secretion from Bowman's glands and vasomotor activity in the olfactory mucosa are regulated by neural elements extrinsic to the primary olfactory neurons. Nerve fibers described in early anatomical studies and characterized by immunohistochemical studies contain a variety of neuroactive peptides and have several targets within the olfactory mucosa. Ultrastructural studies of nerve terminals in the olfactory mucosa have demonstrated the presence of adrenergic, cholinergic and peptidergic input to glands, blood vessels, and melanocytes in the lamina propria and of peptidergic terminals in the olfactory epithelium. The neural origins of the extrinsic nerve fibers and terminals are the trigeminal, terminal, and autonomic systems.

Presence of galanin in rat vagal sensory neurons: evidence from immunohistochemistry and in situ hybridization

Galanin (GAL), a 29 amino acid peptide originally isolated from the porcine upper small intestine, is widely distributed in the rat central nervous system, including the area postrema (AP) and nucleus of the solitary tract (NTS). Although vagal sensory neurons terminate in the AP/NTS, it is not known whether these neurons contain GAL in the rat. Therefore, we examined the presence and distribution of GAL in the rat nodose ganglia which contain the cell bodies of vagal sensory neurons. We used avidin-biotin-peroxidase immunohistochemistry and in situ hybridization histochemistry with a 35S-labeled oligonucleotide probe. Results with both techniques revealed the presence of GAL-containing cell bodies and fibers in the nodose ganglion. GAL-like immunoreactive cell bodies, mostly between 25 and 40 microns in diameter, were unevenly scattered throughout the nodose ganglia. The distribution and cell diameter range of GAL mRNA-labeled neurons appeared similar to those of GAL-like immunoreactive cells. These findings suggest a role for GAL in the transmission of visceral sensory information by the vagus nerve in rats.

Transient expression of somatostatin peptide is a widespread feature of developing sensory and sympathetic neurons in the embryonic rat

Previous studies from this and other laboratories demonstrated that many embryonic sensory ganglion cells in the rat transiently express the catecholamine synthesizing enzyme tyrosine hydroxylase (TH), a trait not expressed by most mature sensory neurons. We, therefore, sought to determine whether transient expression was uniquely associated with catecholaminergic traits, or, alternatively, whether embryonic ganglion cells transiently expressed peptidergic properties as well. Of the four peptides examined (somatostatin [somatotropin release inhibiting factor] (SRIF), galanin (Gal), calcitonin gene-related peptide (CGRP), and substance P (SP)), only SRIF was found to be transiently expressed during early stages of sensory gangliogenesis. Surprisingly, SRIF immunoreactivity was observed in virtually all cranial and spinal sensory ganglion cells on embryonic day (E) 12.5. In addition to perikaryal labeling, intense SRIF immunoreactivity was also observed in the central and peripheral processes of E12.5 sensory neurons, suggesting the peptide may be released from nerve endings. The time course of SRIF appearance in cranial ganglion cells paralleled that previously described for TH, and double-labeling studies revealed extensive co-localization of these two phenotypes. By E16.5, however, the number of neurons expressing SRIF had diminished markedly, indicating that SRIF is only transiently expressed by most sensory neurons during early stages of ganglion development. An unexpected finding was that transient expression of SRIF is also a prominent feature of sympathetic ganglion cells; however, the temporal pattern of staining in the sympathetic and sensory ganglia differed substantially. Whereas virtually no SRIF staining was observed in E12.5 sympathetics, the vast majority of cells in the E16.5 superior cervical ganglion (SCG) were labeled. This contrasted sharply with the adult SCG, in which only low levels of SRIF expression were found. These findings demonstrate that SRIF peptide is transiently expressed at high levels in peripheral sensory and sympathetic neurons during embryogenesis. The time course and widespread distribution of SRIF expression indicates that the peptide may play a role in early stages of ganglion cell growth and development. Moreover, these data, in conjunction with previous studies demonstrating SRIF immunoreactivity in developing central neurons, suggest that transient expression of this peptide is a common property of diverse neuronal cell types.

Galanin-like immunoreactivity in autonomic regions of the rat lumbosacral spinal cord is sexually dimorphic and varies with the estrous cycle

These investigations show that there is a heterogeneous distribution of galanin-like immunoreactivity (GAL-LI) within laminae VII and X of the rat thoraco-sacral spinal cord. In either sex, GAL-LI fibers sparsely outline the position of male and female preganglionic sympathetic neurons in thoracic spinal segments; whereas in lumbosacral segments, far greater numbers of GAL-LI fibers surround autonomic preganglionic neurons. An unusual feature of the GAL-LI fibers in lumbosacral autonomic regions is their sexually dimorphic distribution with males containing greater numbers of GAL-LI fibers than all females examined. In this regard, although the number of GAL-LI fibers observed in males was consistent from animal to animal, the amount of GAL-LI in females fell into two qualitative categories: an 'average' and a 'heavy' amount. These data indicate that the difference in the amount of GAL-LI in the female rat lumbosacral spinal cord is related to the estrous cycle, such that heavy amounts of GAL-LI are observed during proestrus and estrus, while average amounts of GAL-LI are associated with metestrus and diestrus.

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-mediated control of pain: enhanced role after nerve injury

The endogenous inhibitory role of the neuropeptide galanin in pain transmission and spinal cord excitability was demonstrated by the use of a high-affinity galanin receptor antagonist, M-35 [galanin-(1-13)-bradykinin-(2-9)-amide]. M-35, which displaced 125I-labeled galanin from membranes of rat dorsal spinal cord with an IC50 of 0.3 nM, dose-dependently antagonized the effect of intrathecal galanin on the flexor reflex. M-35 potentiated the facilitation of the flexor reflex by conditioning stimulation of cutaneous unmyelinated afferents in rats with intact nerves and the potentiating effect of M-35 on the conditioning-stimulation-induced reflex facilitation of the cutaneous unmyelinated afferents was strongly enhanced after axotomy. These results demonstrate that endogenous galanin plays a tonic inhibitory role in the mediation of spinal cord excitability, and it is particularly noteworthy that this function of galanin is remarkably enhanced after peripheral nerve section.

Effects of intrathecal antibodies to substance P, calcitonin gene-related peptide and galanin on repeated cold stress-induced hyperalgesia: comparison with carrageenan-induced hyperalgesia

Rats exposed to a cold environment (4 degrees C) for 30 min every 1 h during the day and at night show a gradual decrease in the nociceptive threshold for pressure stimulation. Such hyperalgesia, referred to as repeated cold stress (RCS)-induced hyperalgesia, is stable for at least 4 h and maintained for 3 days only by exposing to cold overnight; thus, no adaptation to RCS is apparent. Hyperalgesia gradually returns over 4 days after cold exposure ceases. To determine whether three neuropeptides, substance P (SP), calcitonin gene-related peptide (CGRP) and galanin (GAL), which are present in the superficial dorsal horn including primary afferent terminals, would be responsible for RCS-induced hyperalgesia, we examined the effects of intrathecal injections of their antibodies (used as inhibitors of neuropeptide-mediated synaptic transmission) on the nociceptive threshold of RCS rats, and compared this with the antibody effect on carrageenan-induced hyperalgesia. An intrathecal injection of anti-SP antibody significantly inhibited the hyperalgesia of RCS rats as well as carrageenan-induced hyperalgesia, and slightly increased the nociceptive threshold of non-RCS rats. Anti-CGRP antibody produced an improvement in the hyperalgesia of RCS rats as well as carrageenan-induced hyperalgesia without having an effect on the nociceptive threshold of non-RCS rats. Although anti-GAL antibody significantly inhibited carrageenan-induced hyperalgesia, it did not affect the nociceptive threshold of RCS and non-RCS rats. The present results suggest that enhancement of synaptic transmission mediated by SP and CGRP, but not GAL, in the spinal dorsal horn is, at least in part, involved in RCS-induced hyperalgesia.

Galanin is more common than NPY in vascular sympathetic neurons of the brush-tailed possum

The distribution of galanin (Gal) in sympathetic vascular neurons of adult and juvenile brush-tailed possums (Trichosurus vulpecula), was examined using double-labelling immunohistochemistry. This was compared with the distribution of neuropeptide Y (NPY) in the same tissues. Immunoreactivity (IR) to galanin was present in the majority (64-99%) of nerve cell bodies in paravertebral sympathetic ganglia, where it mostly co-existed with IR to the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH). Gal-IR also was present in most, if not all, TH-IR perivascular axons supplying systemic arteries and veins. NPY-IR was less common than Gal-IR in all sympathetic ganglia and perivascular axons examined. Some sympathetic, TH-IR axons supplying the abdominal aorta and renal artery contained both Gal-IR and NPY-IR, while TH-IR axons supplying cephalic and thoracic vessels contained Gal-IR but not NPY-IR. Limited observations on sympathetic neurons in two species of wallabies indicated that Gal-IR also was more common than NPY-IR in other marsupial species, but the incidence of NPY-IR was higher in these wallabies than in the brush-tailed possum. Together with previous studies, this work suggests that the coexistence of galanin and NPY may be the primitive condition for sympathetic neurons in tetrapods. The differential expression of these peptides in specific populations of sympathetic neurons may have important functional consequences in the autonomic control of the circulation.

Galanin receptors and their second messengers in the lumbar dorsal spinal cord

The ligand binding properties of galanin receptors were examined in crude synaptosomal fraction preparations of lumbar dorsal spinal cord, using chloramin-T mono-iodinated porcine Tyr26 galanin as ligand. The equilibrium binding of [125I]galanin showed the presence of a single population of high-affinity binding sites with KD = 0.6 +/- 0.2 nM in a concentration of 55 +/- 15 fmol mg-1 protein (Bmax). The N-terminal fragments galanin (1-16) and galanin (1-12) fully displaced specific [125I]galanin binding from membranes with IC50 values 6 nM and 4 microM, respectively. The C-terminal fragment galanin (17-29) did not displace [125I]galanin when applied in the concentration range 10(-11)-10(-4) M. GTP inhibited the specific binding of [125I] galanin in a concentration dependent manner, with 54% inhibition at 1 mM, suggesting that the galanin receptor found in lumbar dorsal spinal cord is G-protein coupled. Second messenger systems, through which the galanin receptor in lumbar dorsal spinal cord may exert its effect, were also studied. A galanin (10 microM) produced inhibition (58%) of the depolarization induced cGMP increase was found, whereas galanin (10 microM) did not inhibit the noradrenalin (100 microM) activated cAMP synthesis or phosphoinositide turnover in tissue slices of the spinal cord. Bilateral transection of the sciatic nerve at midthigh level 14 days prior to the binding experiment was performed, a treatment which is known to cause a dramatic increase of galanin-like immunoreactivity in the superficial layers of the dorsal spinal cord, dorsal root ganglion and in galanin mRNA levels, but no significant effect on Bmax or KD of the galanin receptor was found.

Involvement of substance P in hyperalgesia induced by intrathecal galanin

Previously we have demonstrated that an intrathecal injection of galanin (GAL) decreases the nociceptive threshold for mechanical stimulation without effect on thermal nociceptive responses. The present experiments were conducted to determine whether substance P (SP) would be involved in such a decrease in the nociceptive threshold produced by GAL. An intrathecal injection of anti-SP monoclonal antibody inhibited the nociceptive threshold-decreasing effect of intrathecal GAL (0.1 nmol/rat). This antibody significantly suppressed the contractile action of SP (3 nM) on the longitudinal muscle and that of neurokinin A (3 nM) to a lesser degree. Binding of [125I]Tyr8-SP to this antibody was inhibited by SP in a concentration-dependent manner in the range 0.1-33 nM without suppression by GAL at a concentration of 3300 nM. In addition, an intrathecal injection of the anti-SP monoclonal antibody increased the nociceptive threshold for mechanical stimulation in carrageenin-inflamed rats without effect on thermal nociceptive behaviors. The capsaicin (0.5 microM)-evoked release of immunoreactive SP from dorsal-half slices of the spinal cord was increased by galanin (1 microM, but not 0.1 microM) without effects on basal release. An intrathecal injection of GAL did not produce aversive responses (biting, licking and scratching) at doses of 0.1 and 1 nmol/rat. GAL (0.1 nmol/rat) did not affect biting/licking behaviors evoked by SP (1 nmol/rat), but inhibited SP-evoked scratching behavior. These results suggest that the nociceptive threshold-decreasing action of intrathecal GAL is at least in part mediated by SP, and that GAL may act on primary afferent terminals to increase the release of SP evoked by stimulation.

Distribution of galanin-like immunoreactivity in the brain of Rana esculenta and Xenopus laevis

The immunocytochemical distribution of galanin-containing perikarya and nerve terminals in the brain of Rana esculenta and Xenopus laevis was determined with antisera directed toward either porcine or rat galanin. The pattern of galanin-like immunoreactivity appeared to be identical with antisera directed toward either target antigen. The distribution of galanin-like immunoreactivity was similar in Rana esculenta and Xenopus laevis except for the absence of a distinct laminar distribution of immunoreactivity in the optic tectum of Xenopus laevis. Galanin-containing perikarya were located in all major subdivisions of the brain except the metencephalon. In the telencephalon, immunoreactive perikarya were detected in the pars medialis of the amygdala and the preoptic area. In the diencephalon, immunoreactive perikarya were detected in the caudal half of the suprachiasmatic nucleus, the nucleus of the periventricular organ, the ventral hypothalamus, and the median eminence. In the mesencephalon, immunoreactive perikarya were detected near the midline of the rostroventral tegmentum, in the torus semicircularis and, occasionally, in lamina A and layer 6 of the optic tectum. In the myelencephalon, labelled perikarya were detected only in the caudal half of the nucleus of the solitary tract. Immunoreactive nerve fibers of varying density were observed in all subdivisions of the brain with the densest accumulations of fibers occurring in the pars lateralis of the amygdala and the preoptic area. Dense accumulations of nerve fibers were also found in the lateral septum, the medial forebrain bundle, the periventricular region of the diencephalon, the ventral hypothalamus, the median eminence, the mesencephalic central gray, the laminar nucleus of the torus semicircularis, several laminae of the optic tectum, the interpeduncular nucleus, the isthmic nucleus, the central gray of the rhombencephalon, and the dorsolateral caudal medulla. The extensive system of galanin-containing perikarya and nerve fibers in the brain of representatives of two families of anurans showed many similarities to the distribution of galanin-containing perikarya and nerve fibers previously described for the mammalian brain.

Do neuropeptides in the dorsal horn change if the dorsal root ganglion cell death that normally accompanies peripheral nerve transection is prevented?

Peripheral nerve section causes the death of dorsal root ganglion cells and changes in neuroactive peptides in the dorsal horn of the spinal cord. The relationship between these 2 events has not been previously studied, however. One approach would be to prevent sensory cell death and then determine changes in peptide immunoreactivity. To do this, transected rat sciatic nerve stumps were placed in an impermeable silicone tube for one month. The tube was then removed and after 30 additional days the cells were counted. The data indicate that no cell death occurred. We conclude that the sensory cells are first saved due to some factor present in the tube, and then after 30 days, the cells become independent of the tube and its contents. In these same animals, all of the peptides we examined were significantly changed. Four of the peptides, calcitonin gene-related peptide (CGRP), substance P (SP), cholecystokinin octapeptide (CCK) and galanin (GAL) were significantly depleted in the medial L4-L5 superficial dorsal horn, and vasoactive intestinal polypeptide (VIP) was significantly increased. We conclude that there are major changes in spinal peptide systems following peripheral nerve transection even if there is no accompanying death of sensory neurons. Thus we suggest that dramatic central changes in peptide immunoreactivity following peripheral nerve transection are independent of the sensory cell death that usually occurs in response to this injury.

Distribution of 125I-galanin binding sites, immunoreactive galanin, and its coexistence with 5-hydroxytryptamine in the cat spinal cord: biochemical, histochemical, and experimental studies at the light and electron microscopic level

The distribution of galanin-like immunoreactivity (GAL-LI) in the spinal cord of the cat was studied by use of indirect histochemistry and the peroxidase-antiperoxidase (PAP) technique. In the ventral horn GAL-immunoreactive (IR) axonal fibers and terminals were most frequent in the ventral part of the motor nucleus. The GAL-IR axons also contained 5-hydroxytryptamine (5-HT)-LI, and they disappeared after spinal cord transection. It was concluded that these GAL-IR fibers belong to the serotoninergic bublospinal pathway. In the medulla oblongata from normal cats, scattered GAL-IR cell bodies were encountered within the nucleus raphe obscurus and nucleus raphe pallidus. Electron microscopic observations revealed that the fine structure of the GAL-IR axonal boutons in the motor nucleus was similar to that of 5-HT-IR boutons with a varying number of immunoreactive large dense core vesicles. The postsynaptic element in all cases studied was a dendrite. A dense GAL-IR axonal plexus was found in the superficial laminae I-II of the dorsal horn. Coexistence was found between the GAL- and substance P-LI in fibers within the dorsal horn plexus. Spinal cord transection did not alter the pattern of GAL-LI in the dorsal horn, while the vast majority of GAL-IR axonal swellings disappeared following dorsal root sectioning. Electron microscopic observations in lamina II (substantia gelatinosa) revealed that the GAL-IR axonal terminals could be divided into two main groups. One with small to medium-sized axonal boutons formed synaptic contacts with both dendritic and axonal profiles. The other formed the central axon terminals of glomeruli, suggesting that GAL-LI may be present in C-type primary afferents. Numerous small GAL-IR cell bodies were encountered in laminae II and III. GAL-IR cell bodies were also observed in lamina X. The dorsal root ganglia contained a low but consistent number of small to medium-sized GAL-IR cell bodies, which all contained immunoreactive calcitonin gene-related peptide (CGRP). Following peripheral sciatic nerve transection, the number and the labeling intensity of GAL-IR cell bodies in the corresponding dorsal root ganglia showed a moderate increase. Radioimmunoassay revealed that the concentration of GAL-LI increased along the rostrocaudal axis of the normal spinal cord, and was about three times higher in the dorsal than in the ventral regions. The concentration in the dorsal root ganglia was intermediate to those seen in the corresponding dorsal and ventral cord regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution of five peptides, three general neuroendocrine markers, and two synaptic-vesicle-associated proteins in the spinal cord and dorsal root ganglia of the adult and newborn dog: an immunocytochemical study

This study describes the immunocytochemical distribution of five neuropeptides (calcitonin gene-related peptide [CGRP], enkephalin, galanin, somatostatin, and substance P), three neuronal markers (neurofilament triplet proteins, neuron-specific enolase [NSE], and protein gene product 9.5), and two synaptic-vesicle-associated proteins (synapsin I and synaptophysin) in the spinal cord and dorsal root ganglia of adult and newborn dogs. CGRP and substance P were the only peptides detectable at birth in the spinal cord; they were present within a small number of immunoreactive fibers concentrated in laminae I-II. CGRP immunoreactivity was also observed in motoneurons and in dorsal root ganglion cells. In adult animals, all peptides under study were localized to varicose fibers forming rich plexuses within laminae I-III and, to a lesser extent, lamina X and the intermediolateral cell columns. Some dorsal root ganglion neurons were CGRP- and/or substance P-immunoreactive. The other antigens were present in the spinal cord and dorsal root ganglia of both adult and newborn animals, with the exception of NSE, which, at birth, was not detectable in spinal cord neurons. Moreover, synapsin I/synaptophysin immunoreactivity, at birth, was restricted to laminae I-II, while in adult dogs, immunostaining was observed in terminal-like elements throughout the spinal neuropil. These results suggest that in the dog spinal cord and dorsal root ganglia, peptide-containing pathways complete their development during postnatal life, together with the full expression of NSE and synapsin I/synaptophysin immunoreactivities. In adulthood, peptide distribution is similar to that described in other mammals, although a relative absence of immunoreactive cell bodies was observed in the spinal cord.

Substance P-containing sensory neurons in the rat dorsal root ganglia innervate the adrenal medulla

The adrenal medulla is innervated by both cholinergic and substance P (SP)-containing fibres via the splanchnic nerve. SP has been shown to modulate catecholamine (CA) secretion in isolated chromaffin cells and in the perfused rat adrenal gland, however, the origin of SP-containing fibres is not known. In the present study, we have combined the techniques of SP immunohistochemistry and retrograde tracing with Fast blue injected into the left adrenal medulla of the rat in order to study whether SP-containing sensory neurons in the dorsal root ganglia innervate the adrenal medulla. The results showed that there were on average 281 +/- 31 SP-like immunoreactive cells in each left dorsal root ganglion, T3-T13 (range, 234 +/- 19 in T4 to 372 +/- 43 in T13, n = 8). The average total number of Fast blue-labelled cells (T3-T13) in 8 experiments was 172 +/- 26, distributed normally about a peak at T8 (33.8 +/- 6.3 cells) and T9 (33.3 +/- 6.8 cells) with the least at T3 (1.5 +/- 0.8) and T13 (5.2 +/- 2.0). No Fast blue-labelled cells were found in the right DRG. In the left DRG, the average number of cells exhibiting both SP and Fast blue labelled cells were distributed from T7 to T9. These results demonstrate that SP-containing sensory neurons in the dorsal root ganglia provide an ipsilateral innervation of the adrenal medulla in rats.

Localization of NADPH-diaphorase-containing neurons in sensory ganglia of the rat

The presence of reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase activity was studied histochemically in the sensory ganglia of the rat. Supraspinally, the trigeminal ganglion possessed only a few cells positively stained for NADPH-diaphorase, while a large number of positive neurons was found in the nodose ganglion. In the dorsal root ganglia, the distribution of positive cells showed a peculiar pattern in relation to spinal levels. Very minor populations (less than 2% of the total ganglionic cells) exhibited positive reaction in ganglia at levels ranging from the first cervical (C1) to fourth thoracic (T4) and from the second lumber (L2) through the entire sacral levels. In the middle to lower thoracic levels (from T5 to L1), however, abundant diaphorase-positive cells were observed. From these positive neurons it was possible to trace intensely stained nerve fibers. In the lower thoracic level, for example, dense positive fibers were seen in the ramus communicans. Retrograde tracing studies revealed that diaphorase-containing neurons in the lower thoracic level project at least partly to the gastric wall and the celiac ganglion. These results indicate that the diaphorase-positive ganglionic neurons in the thoracicolumbar levels may carry autonomic visceral afferent information. Double staining with NADPH-diaphorase histochemistry and peptide immunohistochemistry revealed that NADPH-diaphorase colocalizes with calcitonin gene-related peptide and substance P in many of these visceral afferent neurons.

Origin of galanin-immunoreactive nerve fibers in the rat paracervical autonomic ganglia and uterine cervix

Retrograde axonal tracing with fluorogold in conjunction with immunohistochemistry was used to examine the source of galanin-immunoreactive nerve fibers in the paracervical ganglia and uterine cervix of the female rat. Immunohistochemistry revealed galanin-immunoreactive neuron somata in lumbosacral dorsal root ganglia and around the central canal of the lumbosacral spinal cord (lamina X). Injection of fluorogold into the paracervical ganglia resulted in labelled cells in dorsal root ganglia and the sacral parasympathetic nucleus of the spinal cord; but fluorogold-labelled, galanin-immunoreactive cells were found only in dorsal root ganglia. Injection of the tracer in the cervix resulted in labelled cells in the paracervical ganglia and dorsal root ganglia; however, fluorogold-labelled, galanin-immunoreactive cells were again evident only in dorsal root ganglia. It is suggested that the galanin-immunoreactive nerve fibers and varicosities in the paracervical ganglia and uterine cervix are sensory fibers from spinal dorsal root ganglia. The galanin-immunoreactive varicosities in the ganglia could play a role in the modulation of pelvic visceral activity, while those in the musculature of the cervix could influence contractility.

Further studies on galanin-, substance P-, and CGRP-like immunoreactivities in primary sensory neurons and spinal cord: effects of dorsal rhizotomies and sciatic nerve lesions

The peptides galanin (GAL), substance P (SP), and calcitonin gene-related peptide (CGRP) were analyzed with immunohistochemistry and radioimmunoassay in the spinal cord, dorsal root ganglia, dorsal roots, and sciatic nerve of normal rats and rats subjected to several experimental procedures, including ligation, crush, and/or sectioning of nerves. The results show that peripheral nerve transection induces a dramatic increase in GAL content both in dorsal roots and sciatic nerve, demonstrating that this lesion causes an increased out-transport of the newly synthesized peptide both into the central and peripheral branches of the primary sensory neurons. In contrast evidence was obtained for decreased out-transport of SP and CGRP. The functional significance of these findings remains to be analyzed.

Intrathecal injections of galanin and its antiserum affect nociceptive response of rat to mechanical, but not thermal, stimuli

To ascertain the involvement of galanin in nociceptive transmission in the spinal dorsal horn, we examined the effects of intrathecal injections of porcine galanin and its antiserum on behavioral nociceptive responses of the rat, using the paw-pressure and paw-radiant heat tests. An intrathecal injection of antiserum against porcine galanin reversed the decreased nociceptive threshold for mechanical, but not thermal, stimulation of the carrageenin-treated hind paw of rat, with no effect on the nociceptive threshold of the non-inflamed hind paw. Rat galanin as well as porcine galanin suppressed the binding of [125I]porcine galanin to the antiserum, a finding suggesting that the antiserum can bind rat galanin. An intrathecal injection of porcine galanin (0.1 and 1 nmol, but not 0.01 nmol) decreased the mechanical nociceptive threshold of the rat hind paw with no effect on thermal nociception. These results suggest that galanin present in the dorsal horn is involved in the facilitation of mechanical, but not thermal, nociceptive transmission.

Sexually dimorphic distribution of a galanin-like peptide in the central nervous system of the teleost fish Poecilia latipinna

Immunohistochemical techniques were used to visualize areas of the brain and spinal cord containing a galanin-like peptide in the teleost fish, the sailfin molly. Galanin-like immunoreactivity (GAL-LI) in both males and females was identified in neurons in the nucleus preopticus periventricularis, nucleus lateralis tuberis, and nucleus commissuralis. GAL-LI fibers had a comparable distribution in the forebrain, preoptic, hypothalamic, and visceral sensory areas of both sexes. In striking contrast to these areas, the optic tectum, torus semicircularis, brainstem tegmentum, and spinal cord of the male contained much higher levels of GAL-LI than the female. GAL-LI in these dimorphic areas in the female was limited to single fiber bundles in the ventromedial tegmentum and in the trigeminal system. Additionally, a population of neurons in the preoptic nucleus was found to contain GAL-LI in the male only. Sexual dimorphism was especially prominent in the spinal cord, where extensive GAL-LI fibers were found in the male only. These fibers were oriented in the longitudinal plane and confined largely to the gray matter. Comparative studies were performed on the goldfish spinal cord, in which GAL-LI was localized solely in the dorsal horn and exhibited no sexual dimorphism. Further, examination of spinal cord material from neonatal mollies revealed a lack of spinal GAL-LI at this developmental stage. As the extent of GAL-LI in the male molly spinal cord differs from both the goldfish and from that reported for the mammalian spinal cord, and a prominent sexual dimorphism in GAL-LI extends from the diencephalon to the caudal spinal cord, it is suggested that a galanin-like peptide may play a unique, sex-specific role in this species.

Source of sexually dimorphic galanin-like immunoreactive projections in the teleost fish Poecilia latipinna

A galanin-like peptide has a sexually dimorphic distribution in the teleost fish, the sailfin molly. An extensive system of galanin-like immunoreactive (GAL-LI) fibers has been described in the brainstem and spinal cord of the male molly, which is absent in the female (Cornbrooks and Parsons, companion paper). As GAL-LI in the mammalian spinal cord has been localized to neurons of origin in the dorsal root ganglia and dorsal and ventral horns, the present study was undertaken to determine whether the sexually dimorphic GAL-LI in the male molly may originate in part from corresponding sources in this species. Colchicine treatments of the spinal cord and dorsal root ganglia did not result in GAL-LI staining in neuronal somata in these regions. Following complete transection of the spinal cord and at any level of the spinal cord, there was a complete absence of GAL-LI caudal to the lesion site. In fish that received unilateral spinal transection, there was a loss of GAL-LI ipsilateral and caudal to the lesion. Finally, in fish that received lesions in the rostral hypothalamus, there was a complete loss of GAL-LI in the sexually dimorphic fiber system in the brainstem and spinal cord, but not in non-dimorphic GAL-LI regions of the brainstem. Thus the sexually dimorphic fiber system in the male molly may originate in neurons of the preoptic nucleus that are sexually dimorphic for a GAL-LI peptide. This preoptico-spinal pathway may mediate sex-specific behaviors in this species.

Intrathecal galanin blocks the prolonged increase in spinal cord flexor reflex excitability induced by conditioning stimulation of unmyelinated muscle afferents in the rat

The effect of intrathecal (i.t.) galanin (GAL) on the prolonged increase of spinal reflex excitability produced by conditioning stimulation (CS) of unmyelinated muscle afferents was studied in decerebrate, spinalized, unanesthetized rats. A CS train (1 Hz, 20 s) applied to the unmyelinated fibers in the gastrocnemius muscle nerve facilitated the ipsilateral flexor for about 1 h. Pretreatment with GAL (0.1-10 microgram) decreased reflex facilitation induced by the gastrocnemius nerve CS. The present results indicate that GAL is capable of blocking the prolonged increase in spinal cord excitability after stimulation of unmyelinated muscle afferents, possibly by antagonizing the facilitatory effect of tachykinins and calcitonin gene-related peptide released at the intraspinal terminals of these fibers.

Peptide-containing nerve fibers in the fungiform papillae of pigs and rats

The occurrence and distribution of an array of neuropeptides and dopamine-beta-hydroxylase in the fungiform papillae of pigs and rats were studied by immunocytochemistry. Structural differences between the fungiform papillae of the two species were correlated to differences in the occurrence and distribution of neuropeptides. Calcitonin gene-related peptide-, substance P- and neurokinin A-containing fibers were numerous in the fungiform papillae of both species, although their distribution within the papilla differed. In the pig, the majority of these fibers ended within the taste buds, while in the rat numerous fibers also penetrated the adjacent epithelium. Galanin- and bombesin-immunoreactive nerve fibers could not be detected in the rat fungiform papillae, while in the pig many, but not all, of the fungiform papillae contained bombesin- and galanin-positive nerve fibers. Vasoactive intestinal peptide- and peptide histidine isoleucine-immunoreactive fibers occurred in the fungiform papillae of both species. A few neuropeptide Y-containing fibers and dopamine-beta-hydroxylase-positive (presumably adrenergic) fibers could be observed in the porcine papillae only.

Spantide II, a novel tachykinin antagonist, and galanin inhibit plasma extravasation induced by antidromic C-fiber stimulation in rat hindpaw

The effect of intradermal injection of Spantide II, a novel tachykinin antagonist, and the neuropeptide galanin on neurogenic plasma extravasation induced by antidromic stimulation of C-fibers in the sciatic nerve was examined in the hindpaws of rats. Activation of C-fibers by antidromic sciatic nerve stimulation (2 Hz, 5 min) consistently evoked a localized plasma extravasation of Evans Blue in the skin area of the hindpaw innervated by the sciatic nerve. Intradermal injection of 3 nmol Spantide II significantly inhibited this response. The plasma extravasation was nearly totally abolished when the concentration of Spantide II was increased to 9 nmol. Intradermal injection of 1.5 and 15 nmol galanin also inhibited plasma extravasation. Intradermal injection of 9 nmol Spantide II effectively blocked the plasma extravasion in the hindpaw induced by 8 nmol intravenous substance P. Plasma extravasation induced by intravenous substance P was also inhibited by the higher, but not by the lower, dose of galanin injected intradermally. The present results indicate that Spantide II, a potent non-toxic tachykinin antagonist, effectively blocks the neurogenic plasma extravasation induced by antidromic C-fiber stimulation, thus supporting the view that tachykinins play an important role in this neurogenic inflammatory process. It is further shown that galanin, a naturally occurring neuropeptide present in primary afferents, also inhibits C-fiber activation-evoked plasma extravasation, indicating an interaction between galanin and tachykinins in the peripheral terminals of primary afferents, possibly through both pre- and postsynaptic mechanisms.

Capsicum--production, technology, chemistry, and quality. Part V. Impact on physiology, pharmacology, nutrition, and metabolism; structure, pungency, pain, and desensitization sequences

The spice Capsicum is the fruit of the cultivated species of the genus Capsicum (family, Solanaceae), C. annuum principally, and C. frutescens L. to a lesser extent. A third variety of C. annuum var. annuum fruits, the large-sized, fleshy bell capsicum is used as a fresh vegetable and valued for its aroma, color, and crisp texture, but with no pungency. This variety is not considered in this series of reviews covering primary processing, production, international trade, chemistry, and biochemistry of functional components--the red keto carotenoids, the aromatic volatiles and the pungent capsaicinoids in Parts I to III. The valid qualitative aspects correlating the specific components of capsicum and their sensory responses are critically covered in Part IV. In this the concluding part of the series of reviews, the significant preference of the spice for initially evoking an aversive response, its potent physiological and pharmacological effects, and the aspects of structure-activity relationships of the pungent stimuli of the capsaicinoids are reviewed. The beneficial effects particularly associated with long usage by some ethnic groups and its safe consumption levels, with a critical review of the studies on the gastrointestinal tract, the cardiovascular system, the sensory system, thermoregulation, nutritional impacts, and an overview of the five series is also detailed.

Capsaicin as a tool for studying sensory neuron functions

The exceptional selectivity with which capsaicin acts on a population of peptide-containing thin primary afferent neurons has made this drug an important tool with which to investigate the neuroanatomical, neurochemical and functional implications of these neurons. As a consequence, the use of capsaicin has enabled a substantial furthering of our understanding of the physiological and pathophysiological roles of thin primary sensory neurons. With appropriate controls, both the acute excitatory and long-term neurotoxic actions of capsaicin can be utilized in these studies but it is important to know the advantages and disadvantages and the limitations of each of the different experimental approaches. Table 1 is a brief checklist of the caveats that should be considered and that have been dealt with in this article.

Distribution of galanin-immunoreactive nerve fibers in the rat nasal mucosa

Galanin-like immunoreactivity was found in nerve fibers beneath and within the epithelium of the rat mucosa by the use of immunohistochemical techniques. Immunoreactive fibers were also noted close to blood vessels and seromucous glands in the lamina propria. Fast blue applied to the nasal mucosa underwent retrograde transport to some immunoreactive neurons of the trigeminal ganglion. Thus, the rat nasal mucosa was shown to be innervated by galanin-containing sensory nerves.

Galanin immunoreactivity in the mudpuppy cardiac ganglion

The source of galanin-immunoreactive fibers in the cardiac ganglion and on cardiac muscle in mudpuppy (Necturus maculosus) has been determined utilizing immunohistochemical techniques. The galanin-immunoreactive fibers are not processes of afferent fibers originating in either the rostral four dorsal root ganglia or vagal sensory ganglia. Following colchicine treatment, all of the postganglionic parasympathetic neurons and a subpopulation of the small intrinsic neurons in the cardiac ganglion exhibit galanin immunoreactivity. The majority of the galanin-immunoreactive fibers that form complexes on the parasympathetic postganglionic neurons are derived from galanin-immunoreactive small intrinsic neurons, although some of these connections may represent collateral processes from other parasympathetic postganglionic neurons. All of the galanin-immunoreactive processes that innervate cardiac muscle are derived from postganglionic parasympathetic neurons in the cardiac ganglion.

The N-terminal 1-16, but not C-terminal 17-29, galanin fragment affects the flexor reflex in rats

The biological activity of two galanin (GAL) fragments, GAL-(1-16) and GAL-(17-29), was tested in vivo by using a spinal nociceptive flexor reflex model in the rat. Intrathecal (i.t.) GAL-(1-16) had a similar biphasic effect on the flexor reflex, with facilitation at lower doses and facilitation followed by depression at higher doses, as the full length peptide GAL-(1-29). GAL-(1-16) also effectively depressed the facilitation of the flexor reflex caused by i.t. substance P (SP) or C-fiber conditioning stimulation (CS) and potentiated the depressive effect of i.t. morphine on the reflex, both actions that have been reported earlier with GAL-(1-29). In contrast, i.t. GAL-(17-29), even at high doses, did not induce changes in the amplitude of the flexor reflex, nor did it interact with the effects of i.t. SP, morphine or C-fiber CS. It is concluded that the N-terminal portion of GAL-(1-29) is critical for the biological activity of the intact peptide in the dorsal horn of the rat spinal cord. The similarity between the effects of GAL-(1-16) and GAL-(1-29) indicates that they probably act on the same GAL receptor.

Percentages of dorsal root axons immunoreactive for galanin are higher than those immunoreactive for calcitonin gene-related peptide in the rat

The present study shows that 28% of the myelinated and 27% of the unmyelinated axons in the L5 and S1 rat dorsal roots are immunolabeled for galanin. By contrast only 10% of the myelinated and 15% of the unmyelinated axons are immunolabeled for calcitonin gene-related peptide, which is the numerically predominant primary afferent peptide marker for dorsal root ganglion cells. Thus galanin, because of its presence in so many primary afferent fibers, emerges as an important primary afferent marker. In addition, since our data also show that galanin is present predominantly in unmyelinated and fine myelinated sensory axons, a hypothesis is that it is particularly concerned with the transmission of noxious information.

Intrathecal galanin potentiates the spinal analgesic effect of morphine: electrophysiological and behavioural studies

The interaction between intrathecally (i.t.) applied galanin (GAL) and morphine was examined in electrophysiological and behavioural experiments. The physiological experiments were performed on decerebrate, spinalized, unanesthetized rats where the effects of i.t. GAL and morphine on the hamstring flexor reflex were studied. In the behavioural experiments sensitivity to noxious thermal stimulation was assessed on the hot plate test in rats injected with GAL and morphine via chronically implanted i.t. catheters. GAL at 100 ng in 10 microliters, which by itself has no depressive effect, potentiated the depressive effect of morphine on the flexor reflex. In the behavioral study the same dose of GAL potentiated the antinociceptive effect of morphine on the hot plate test without having an analgesic effect by itself. It is suggested that GAL may enhance the analgesic effect of opiates in the spinal cord.

The expression of different cytochemical markers in normal and axotomised dorsal root ganglion cells projecting to the nucleus gracilis in the adult rat

Rat lumbar dorsal root ganglion neurones projecting to the nucleus gracilis in the brainstem were retrogradely labelled with Fluoro-Gold and analysed immunocytochemically for their expression of substance P-, calcitonin gene-related peptide-, galanin-, galanin message-associated peptide-, neuropeptide Y-, nitric oxide synthase- and carbonic anhydrase-like immunoreactivity as well as affinity to Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4, RT97 and to choleragenoid. The analysis was made both in uninjured rats and in rats which had been subjected to unilateral sciatic nerve transection and partial resection 3 weeks earlier. The data showed that 6% of the L4 and L5 lumbar dorsal root ganglion cells that projected to the nucleus gracilis showed substance P-like immunoreactivity. Following nerve injury, none of the nucleus gracilis-projecting dorsal root ganglion cells showed substance P-like immunoreactivity. Nineteen per cent of the investigated cell population showed calcitonin gene-related peptide-like immunoreactivity in uninjured rats, but no nucleus gracilis-projecting calcitonin gene-related peptide-positive cells were found after nerve injury. Galanin- and galanin message-associated peptide-like immunoreactivity were found in 2% and 3%, respectively, of the Fluoro-Gold-labelled cell population normally and in 22% and 14%, respectively, after injury. No neuropeptide Y-positive cells were found in the Fluoro-Gold-labelled cell population normally, but after nerve injury, 96% of this population became neuropeptide Y-positive. Nitric oxide synthase-like immunoreactivity was found in 2% of the Fluoro-Gold-labelled cells normally and in 10% after injury. Two per cent of the Fluoro-Gold-labelled cells in the normal cases were stained by Griffonia (bandeiraea) simplicifolia lectin I--isolectin B4. After injury, however, no such double labelling was found. Thirty-four per cent of the Fluoro-Gold-labelled cell population was carbonic anhydrase positive normally, and 42% after injury. Seventy-five per cent of the Fluoro-Gold-labelled cells showed RT97 immunoreactivity normally and 12% after injury. Choleragenoid-like immunoreactivity was found in 99% of the Fluoro-Gold-labelled dorsal root ganglion cells normally and 81% after injury. Immunohistochemical visualisation of choleragenoid transganglionically transported from the injured sciatic nerve combined with neuropeptide Y immunocytochemistry showed that primary afferent fibres and terminals in the nucleus gracilis contain neuropeptide Y following peripheral nerve transection. Taken together, the results indicate that peripherally axotomised nucleus gracilis-projecting neurones undergo marked alterations in their cytochemical characteristics, which may be significant for the structural and functional plasticity of this system after injury.

Analysis of the ontogeny of galanin in the rat central nervous system by immunohistochemistry and radioimmunoassay

The development of galanin-like immunoreactivity in the rat central nervous system has been investigated immunologically. Galanin-positive processes in the central nervous system were first recognized at day 1 post-natal, in the dorsal horn of the spinal cord. At day 2, the first galanin-immunoreactive neuronal somata were visualized in several regions of the diencephalon; at later stages of maturation positive cells were also detected in many brain stem areas. The number, density and staining intensity of galanin-positive structures in these and other regions increased steadily until day 28, by which age the adult disposition was attained. Increases in the concentrations of galanin-like immunoreactivity during maturation of the animals closely paralleled the immunohistochemical findings. No reduction in galanin-like immunoreactivity was noted in any area during later post-natal ages. The present study indicates that the ontogeny of galanin-like immunoreactivity in the rat central nervous system occurs entirely post-natally. The developmental profile is consistent with the role of galanin as a putative neurotransmitter/neuromodulator in the rat brain and spinal cord.

The co-localization of neuropeptides in the submucosa of the small intestine of normal Wistar and non-diabetic BB rats

Immunocytochemical double and triple staining techniques were employed on whole mounts of the submucosal plexus from normal Wistar and non-diabetic BB rat jejunum and ileum, to determine the patterns of co-localization of vasoactive intestinal polypeptide-, peptide histidine-isoleucine-, somatostatin-, neuropeptide Y-, calcitonin gene-related peptide-, substance P-, and galanin-immunoreactive nerves. Neuropeptide Y immunoreactivity was found in 38% of submucosal plexus neurons, within the same neuronal elements as vasoactive intestinal polypeptide immunoreactivity (39% of submucosal plexus neurons) and peptide histidine-isoleucine immunoreactivity. A small population (1% of submucosal plexus neurons) containing vasoactive intestinal polypeptide- and peptide histide isoleucine-like immunoreactivity without NPY-like immunoreactivity was also observed. A significant population of fibers containing vasoactive intestinal polypeptide and galanin immunoreactivity were observed in the mucosa and submucosa, although no cell bodies were detected which contained both neuropeptides. Galanin-like immunoreactivity was seen in a small (2% of submucosal plexus neurons) population, not co-localized with any of the other neuropeptides examined. All somatostatin-immunoreactive neuronal elements (18% of submucosal plexus neurons) contained calcitonin gene-related peptide immunoreactivity, just over half of which also contained substance P immunoreactivity. An additional 25% of submucosal plexus neurons contained calcitonin gene-related peptide- without somatostatin-like immunoreactivity and 28% of submucosal plexus neurons contained substance P without somatostatin-like immunoreactivity. Some degree of co-localization was seen between calcitonin gene-related peptide- and substance P-like immunoreactivity, however, this could not be directly quantified.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of intrathecal galanin on the flexor reflex in rat: increased depression after sciatic nerve section

The effect of intrathecal galanin (GAL) on the hamstring flexor reflex to sural nerve stimulation was compared in rats with intact and unilaterally sectioned sciatic nerves. GAL had a biphasic effect on the flexor reflex in rats with intact nerves, including facilitation, facilitation followed by depression and pure depression, in a dose-dependent manner. In axotomized rats, the depressive effect of GAL was significantly increased, occurring at lower drug concentrations. Furthermore, the degree of depression was significantly stronger with a more rapid onset after nerve section. It is concluded that along with an increase in GAL-like immunoreactivity in primary afferents, the inhibitory function of this neuropeptide is enhanced following axotomy. This functional change may be due to both pre- and postsynaptic mechanisms.