Distribution of tyrosine hydroxylase and neuropeptide Y-like immunoreactive neurons in rabbit medulla oblongata, with attention to colocalization studies, presumptive adrenaline-synthesizing perikarya, and vagal preganglionic cells

Co-localization of neurotensin- and cholecystokinin-like immunoreactivities in catecholamine neurons in the rat dorsomedial medulla

Co-localization of neurotensin and cholecystokinin in tyrosine hydroxylase-containing neurons in the nucleus tractus solitarius of the rat was demonstrated by immunocytochemistry with fluorescent double-staining combined with the peroxidase-antiperoxidase method. Co-localization of neurotensin/tyrosine hydroxylase or cholecystokinin/tyrosine hydroxylase was consistently found in small neurons in the region dorsomedial to the tractus solitarius at the level of the area postrema with high percentages of co-existence: 91.0% tyrosine hydroxylase-immunoreactive neurons contained neurotensin and 91.1% cholecystokinin, suggesting that they represent the same neurons. Accordingly, co-localization of neurotensin and cholecystokinin was assessed on tyrosine hydroxylase-containing neurons bisected into two adjacent sections, and then identified in a certain number of the catecholamine neurons in this region. Furthermore these catecholamine neurons exhibited immunoreactivity for an adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase. It was concluded that catecholamine, in particular adrenaline, neurons, characterized by co-localization of neurotensin and cholecystokinin, established a distinct subpopulation in the catecholaminergic system in the dorsomedial medulla of the rat.

Cardiovascular role of the major noradrenergic cell groups in the rabbit: analysis based on 6-hydroxydopamine-induced transmitter release

We examined the role of the noradrenergic (NA) neurons of the A1, A2, A1 + A2, A5 and A6 + A7 regions on mean arterial pressure (MAP) and heart rate (HR), by comparing the acute responses of chronically lesioned and sham-operated rabbits to intracisternal 6-hydroxydopamine (6-OHDA, 600 micrograms/kg) which induces central release of transmitter. We studied rabbits (1) with intact arterial baroreceptors (non-denervated) and (2) after sino-aortic denervation (SAD). The acute transmitter release response consisted of an early fall in MAP (observed in SAD rabbits) and a late rise in MAP (observed in both non-denervated and SAD rabbits). Medullary lesions had no effect on either MAP component, but A5 and A6 + A7 lesions attenuated both pressor and depressor responses. Normally the transmitter release-induced MAP responses are modified by baroreceptor feedback. The 6-OHDA-induced HR changes were vagal in non-denervated rabbits and were sympathetically mediated in SAD rabbits. In non-denervated rabbits, A1, A2 and A1 + A2 lesions affected mainly the early vagal component, whilst A6 + A7 lesions affected the late vagal component. In SAD rabbits the early bradycardia was due to sympathetic inhibition and the late tachycardia due to sympathetic excitation; A1 + A2 lesions and A5 lesions attenuated the sympathetic bradycardia. We conclude that the various components of the MAP and HR responses are mediated through distinctive NA pathways; the deficits of a given lesion could be due to either to loss of NA cell bodies or of NA fibers of passage.

Neuropeptide Y: presence in perivascular noradrenergic neurons and vasoconstrictor effects on skeletal muscle blood vessels in experimental animals and man

The presence of neuropeptide Y (NPY)-like immunoreactivity (-LI) in sympathetic perivascular nerves and the functional effects of NPY and noradrenaline (NA) on vascular tone were studied in skeletal muscle of various species. A dense network of NPY-LI was found around arteries and arterioles but not venules in the gluteus maximus muscle of man, gracilis muscle of dog, tenuissimus muscle of rabbit and quadriceps muscle of cat, rat, guinea pig and pig. The distribution of NPY-immunoreactive (-IR) nerves was closely correlated to the presence of tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH)-positive fibers, two markers for noradrenergic neurons. Double-staining experiments revealed that NPY- and TH-IR as well as NPY- and DBH-IR nerve fibers around arteries and arterioles were identical. The veins and venules, however, lacked or had a very sparse innervation of NPY-, TH- and DBH-positive fibers. The NPY- and TH-IR nerves in quadriceps muscle of the guinea pig were absent after treatment with 6-hydroxydopamine. Lumbosacral sympathetic ganglia from the same species contained many NPY-positive cells which were also TH- and DBH-IR. NPY-LI was also detected by radioimmunoassay in extracts of skeletal muscle from guinea pig, rabbit, dog, pig and man as well as of lumbosacral sympathetic ganglia. The content of NPY-LI in skeletal muscle was relatively low (0.1-0.4 pmol/g), whereas lumbosacral sympathetic ganglia had a much higher content (48-88 pmol/g). NPY (10(-7) M) contracted arterioles in the tenuissimus muscle of the rabbit to a similar extent (by 65%) as NA (10(-6) M), as studied by intravital microscopy in vivo. NPY had no effect on the corresponding venules while NA caused a slight contraction of these vessels. In vitro studies of small human skeletal muscle arteries and veins revealed that NPY was more potent than NA in contracting the arteries, and the highest concentration of NPY (5 x 10(-7) M) caused a contraction of a similar magnitude as NA 10(-5) M. NA contracted veins from human skeletal muscle, while NPY had only small effects. It is suggested that NPY, together with NA, could be of importance for sympathetic control of skeletal muscle blood flow.

Somatostatin and neuropeptide Y are almost exclusively found in the same neurons in the telencephalon of turtles

In mammals, somatostatin and neuropeptide Y (NPY) are largely found in the same neurons of the telencephalon. To determine if this is a phylogenetically ancient feature of telencephalic organization, the brain of red-eared turtles was examined using immunofluorescence double-labeling procedures. The results showed that somatostatin and NPY are found almost exclusively in the same neurons in the telencephalon of turtles, but these neuropeptides rarely co-occur in neurons outside the telencephalon. Thus, the extensive co-occurrence of NPY and somatostatin appears to be a feature of telencephalic organization that was present in the reptilian common ancestors of mammals and modern reptiles.

Increased dopamine-beta-hydroxylase-like immunoreactivity in non-noradrenergic axons supplying the guinea-pig uterine artery after 6-hydroxydopamine treatment

We have reinvestigated the immunohistochemistry of autonomic axons supplying the guinea-pig uterine artery to determine whether non-noradrenergic paracervical ganglion neurons projecting to the artery contain immunoreactivity to dopamine-beta-hydroxylase (DBH) or somatostatin (SOM) in addition to neuropeptide Y (NPY) and vasoactive intestinal peptide (VIP). In untreated arteries no VIP axons had immunoreactivity to tyrosine hydroxylase (TH), although 9% had immunoreactivity to DBH. Somatostatin immunoreactivity was detected in 25% of non-noradrenergic axons containing NPY and VIP. After in vivo treatment with 6-hydroxydopamine (6-OHDA), noradrenergic axons containing immunoreactivity to NPY, DBH and TH were absent from the adventitia-medial junction. However, 65-70% of the non-noradrenergic axons with NPY and VIP showed DBH immunoreactivity after 6-OHDA. These axons did not show catecholamine fluorescence after incubation with pargyline together with noradrenaline, dopamine or L-DOPA. The number of axons with SOM immunoreactivity increased by 44% after 6-OHDA treatment, but only 24% of SOM axons had DBH immunoreactivity. Surgical destruction of the non-noradrenergic autonomic axons in 6-OHDA-treated animals led to the loss of all DBH immunoreactivity. These results demonstrate that DBH immunoreactivity can be detected in a small proportion of non-noradrenergic axons supplying uterine arteries from untreated animals. After chemical sympathectomy with 6-OHDA, the levels of DBH immunoreactivity in axons of non-noradrenergic neurons increased, and more axons with DBH immunoreactivity were detected. DBH immunoreactivity seemed to increase preferentially in axons with NPY and VIP, but not SOM. The number of NPY, VIP axons containing SOM also increased after 6-OHDA. These findings demonstrate that peripheral neurons containing several different potential neurotransmitters can change their levels of neuropeptides and transmitter-synthesizing enzymes in response to local environmental changes.

Co-existence of neuropeptides in sympathetic, cranial autonomic and sensory neurons innervating the iris of the guinea-pig

We have used double-labelling immunofluorescence to identify the peptide content of autonomic and sensory neurons innervating the iris of albino guinea-pigs. Four major classes of neurons were identified on the basis of their distributions, origins and immunohistochemical characteristics. A dense plexus of noradrenergic axons in the constrictor and dilator muscles of the iris originated from the superior cervical ganglion, and contained immunoreactivity (IR) to both neuropeptide Y (NPY) and dynorphin (DYN). The constrictor and dilator muscles were also supplied with a dense plexus of axons with IR to substance P (SP). These axons probably originated from SP-IR nerve cell bodies located along the ciliary nerves, and are almost certainly the same axons as those producing cholinergic pupilloconstriction. The iris was also innervated by unmyelinated, capsaicin-sensitive axons with IR to both SP and calcitonin gene-related peptide. Most of these axons also contained IR to DYN and some were also IR for cholecystokinin. These axons are almost certainly sensory. Axons containing IR to both NPY and vasoactive intestinal peptide (VIP) were common in the ciliary processes, and also formed a sparse plexus near the ciliary margin of the dilator muscle. Following surgical sympathetic denervation these axons showed IR for dopamine-beta-hydroxylase; they seemed to originate from the sphenopalatine ganglion. These results demonstrate that there are well-defined patterns of coexistence of neuropeptides in the autonomic and sensory neurons supplying the iris of guinea-pigs. To understand the physiological roles of these peptides, it will be necessary to consider the possibility of complex interactions between them.

Inhibition of vasodepressor neurons in the caudal ventrolateral medulla of the rabbit increases both arterial pressure and the release of neuropeptide Y-like immunoreactivity from the spinal cord

The role of bulbospinal neuropeptide Y (NPY)-containing neurons of the rostral ventrolateral medulla in the rabbit in mediating the increase in blood pressure that occurs during inhibition of cells in the caudal ventrolateral medulla was investigated in urethane-anaesthetized rabbits. In the present experiments bilateral injections of the GABA agonist, muscimol, into the caudal ventrolateral medulla elicited a slowly-developing rise in arterial pressure that was maximal 15 min after the injection. Accompanying this increase in arterial pressure was an increase in the release of NPY-like immunoreactivity (NPY-LI) into the spinal subarachnoid space. This pattern of response is similar to that seen after direct chemical stimulation of the NPY-containing cells of the rostral ventrolateral medulla. Taken together, these findings suggest that tonically active neurons in the caudal ventrolateral medulla exert their effects by inhibiting sympathoexcitatory NPY-containing neurons whose cell bodies are situated in the rostral ventrolateral medulla.

The relationship of terminals containing neuropeptide Y-like immunoreactivity to lumbar sympathetic vasoconstrictor neurones in the rabbit

The distributions of preganglionic neurones retrogradely labelled with horseradish peroxidase and of immunohistochemically identified varicose axons reactive for neuropeptide Y (NPY-IR) in the intermediate zone of rabbit lumbar spinal segments have been compared. Neurones projecting in the caudal lumbar sympathetic chain (LSC), which are mainly vasoconstrictor, were located laterally, associated with dense accumulations of NPY-IR terminals in mid L3 to caudal L4. In all other regions of the lumbar intermediate zone, there was relatively little correlation between the location of either LSC neurones, or those projecting to the pelvic viscera, and aggregations of NPY-IR axons. Most of these axons probably arise in the C1 nucleus, but it seems possible that this nucleus innervates only some groups of lumbar vasoconstrictor neurones.

Neurons in the area postrema are the only catecholamine-synthesizing cells in the medulla or pons with projections to the rostral ventrolateral medulla (C1-area) in the rabbit

We have identified, in the rabbit medulla and pons, neurons which project to the C1-region of the rostral ventrolateral medulla. By combining tyrosine hydroxylase immunohistochemistry with retrograde transport of Fluoro-Gold we determined whether any of the retrogradely labelled neurons synthesize catecholamines. The only doubly labelled cells were located in the area postrema. No other group of catecholamine-synthesizing neurons in either the medulla or the pons was found to project to the C1-area of the rostral ventrolateral medulla. Pharmacological agents which lower arterial pressure by stimulating adrenoceptors in the rostral ventrolateral medulla may act on receptors which are not innervated by catecholamine-synthesizing perikarya located outside the C1-region.

Origin of serotonin innervation of the arcuate and ventromedial hypothalamic region

Combined fluorescence serotonin immunohistochemistry and retrograde transport labelling with Fast blue and Fluoro-gold were used to identify serotonin-immunoreactive neurons in the midbrain and pons which project to the region of the arcuate and ventrome-dial hypothalamic nuclei. Approximately 90% of doubly labelled neurons were located in the 3 major mesencephalic serotonin-containing cell groups: dorsal raphe (38%), median raphe (21%) and medial lemniscus group (29%). Within these groups, there were numerous non-retrogradely labelled serotonin-immunoreactive neurons as well as numerous non-serotonin-immunoreactive retrogradely labelled neurons. No doubly labelled neurons were observed caudal to raphe pontis although non-serotonin-immunoreactive neurons were retrogradely labelled in the more caudal raphe nuclei.

Coexistence of peptides with classical neurotransmitters

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

Neuropeptide Y injected into the supraoptic nucleus causes secretion of vasopressin in the unanesthetized rat

Injection of neuropeptide Y (NPY, 0.01-1.0 nmol in 0.25 microliter vehicle) into the supraoptic nucleus of unanesthetized rats increased plasma vasopressin, measured by radioimmunoassay, to a maximum of 90 +/- 18 ng/liter. Injections of vehicle or somatostatin did not increase plasma vasopressin, nor did injections of NPY into the amygdala. Double-labelling immunohistochemical studies demonstrated that fibers containing NPY-like immunoreactivity form a close association with vasopressin immunoreactive perikarya in the supraoptic nucleus. It appears that NPY may directly excite vasopressin-containing neurons causing secretion of vasopressin.

Effects of 6-hydroxydopamine and the PNMT inhibitor LY134046 on pressor responses to stimulation of the subretrofacial nucleus in anaesthetized stroke-prone spontaneously hypertensive rats

The subretrofacial nucleus of the rostral ventrolateral medulla is an important site for the control of sympathetic vasomotor tone and is the location of the C1 PNMT-containing cell bodies. In the present study the involvement of central monoaminergic neurons in the pressor responses evoked by chemical or electrical stimulation of this nucleus was examined in urethane-anaesthetized stroke-prone spontaneously hypertensive rats (SHRSP). Vehicle-treated rats were compared to animals treated with the PNMT inhibitor LY134046, the catecholamine neurotoxin 6-hydroxydopamine (6-OHDA) or a combination of 6-OHDA and the serotonin neurotoxin 5,7-dihydroxytryptamine (5,7-DHT). LY134046 caused a 43% depletion of adrenaline content in the hypothalamus and medulla but not in the spinal cord but had no effect on the pressor responses to stimulation of the subretrofacial nucleus. However, intraventricular administration of 6-OHDA reduced the pressor responses to subretrofacial nucleus stimulation by 50%. 6-OHDA caused profound depletion of noradrenaline in the brain and spinal cord, and adrenaline in the hypothalamus. Combined treatment with 6-OHDA and 5,7-DHT caused the additional depletion of serotonin to 34% and 13% in the hypothalamus and spinal cord, respectively, but caused no further reduction of pressor responses than with 6-OHDA alone. These results suggest that the pressor responses elicited by subretrofacial nucleus stimulation involve a 6-OHDA-sensitive pathway (presumably catecholaminergic) other than the bulbospinal adrenaline pathway but that serotonergic mechanisms do not contribute.

Neuropeptide Y-like immunoreactive C1 neurons in the rostral ventrolateral medulla of the rabbit project to sympathetic preganglionic neurons in the spinal cord

After injection into the thoracic spinal cord of the rabbit, gold particles coupled to concanavalin A were found in the rostral ventrolateral medulla in neurons which contained neuropeptide Y-like immunoreactivity. These cells have previously been shown to belong to the C1 catecholamine (presumably adrenaline)- synthesizing group. Nerve terminals in the intermediolateral column contained both tyrosine hydroxylase and neuropeptide Y-like immunoreactivity. When fast blue was injected into the adrenal gland the retrogradely labeled preganglionic neurons were shown to be surrounded by nerve terminals containing neuropeptide Y-like immunoreactivity. Our results indicate that at least some of these terminals derive from C1 neurons which also synthesize neuropeptide Y.

Microinjection of kainic acid into the rostral ventrolateral medulla causes hypertension and release of neuropeptide Y-like immunoreactivity from rabbit spinal cord

Microinjections of kainic acid were made into the pressor area of the rostral ventrolateral medulla oblongata of anaesthetized rabbits, in the region of the C1 adrenaline-containing neurons. Over the 65 min following the microinjection, there was a significant increase in blood pressure, as well as an increase in the release of neuropeptide Y-like immunoreactivity into the spinal subarachnoid space. These data provide evidence for a functional bulbospinal neuropeptide Y-containing projection which may be responsible for mediating the pressor effects of stimulation of the rostral ventrolateral medulla.

Neurons (presumably A1-cells) projecting from the caudal ventrolateral medulla to the region of the supraoptic nucleus respond to baroreceptor inputs in the rabbit

Extracellular recordings were made in the caudal ventrolateral medulla from 29 neurons that could be antidromically activated from the region of the supraoptic nucleus in the rabbit. The median axonal conduction velocity was 0.8 m/s. Of 15 cells tested only one did not respond to some form of baroreceptor input. Fourteen were inhibited by experimentally increasing arterial pressure and 8 were excited by decreasing arterial pressure. Stimulation of the aortic depressor nerve decreased the discharge rate of 8 out of 12 cells tested. The location and projections of these neurons suggest that they were A1 noradrenaline-synthesizing cells.

Co-localization of N-acetyl-aspartyl-glutamate in central cholinergic, noradrenergic, and serotonergic neurons

An immunohistochemical technique for simultaneously visualizing two different antigens has been used to investigate the presence of the acidic dipeptide, N-acetyl-aspartyl-glutamate (NAAG), in cholinergic, noradrenergic-adrenergic, and serotonergic neurons within CNS. The brain slices were processed sequentially with purified antisera against NAAG and then monoclonal antibody against choline acetyltransferase (ChAT), a marker for cholinergic neurons, or antiserum against dopamine-beta-hydroxylase (DBH), a marker of noradrenergic-adrenergic neurons, or antiserum against serotonin (5HT). Both antigens were revealed by the peroxidase reaction but with different chromogens, which are easily distinguishable. An intense double staining of NAAG-like immunoreactivity (NAAG-LI) and ChAT was observed in the motoneurons of the spinal cord as well as in the several motor components of cranial nerve nuclei including facial, ambiguus, and trigeminal nuclei. A partial colocalization of NAAG-LI and ChAT was evident in the perikarya of the basal forebrain cholinergic system, whereas cholinergic neurons of the medial septum exhibited only sporadic staining for NAAG-LI. A complete coexistence of NAAG-LI and DBH was observed in the locus coeruleus. Most of the other noradrenergic and adrenergic cell groups of the medulla region exhibited substantial co-localization with the exception of the A2 cell group, which was virtually devoid of NAAG-LI. In the dorsal raphe, only a low percentage of serotonergic neurons stained for NAAG-LI. The co-existence of NAAG-LI and serotonin was more evident in the neurons of the median raphe, although the majority of cells failed to show double staining.(ABSTRACT TRUNCATED AT 250 WORDS)

The immunohistochemical distribution of neuropeptide Y in lumbar pre- and paravertebral sympathetic ganglia of the guinea pig

Neuropeptide Y (NPY)- like immunoreactive nerve cell bodies and nerve fibres have been studied in normal and colchicine-treated ganglia of the caudal lumbar sympathetic chain (LSC) and the inferior mesenteric ganglion (IMG) of the guinea pig. The great majority of noradrenergic ganglion cells in the LSC (defined as containing tyrosine hydroxylase immunoreactivity), but less than 20% of those in the IMG, were NPY-positive. These proportions correspond well to the proportions of neurones that have been found to discharge phasically in electrophysiological experiments on the same ganglia. As noradrenergic terminals innervating blood vessels contain NPY, the data are consistent with the idea that phasic discharge is a characteristic of vasoconstrictor neurones.