Immunohistochemical identification of noradrenaline- and adrenaline- synthesizing neurons in the cat ventrolateral medulla

Estrogen alters the bradycardia response to hypocretin-1 in the nucleus tractus solitarius of the ovariectomized female

Experiments were performed to investigate the effect of 17beta-estradiol (E; 30 pg/ml plasma) treatment (15-25 days) in the ovariectomized (OVX) female Wistar rat on the cardiovascular responses to hypocretin-1 (hcrt-1) in the nucleus tractus solitarius (NTS). In an initial series of experiments, the distribution of hcrt-1-like immunoreactivity within the region of the NTS was mapped in both OVX only and OVX+E animals. Hcrt-1 immunoreactivity was found throughout the NTS region in both groups of females, predominantly within the caudal interstitial, commissural, medial and lateral subnuclei of the NTS. The relative density of hcrt-1 immunoreactivity in all NTS subnuclei was similar in both female groups. Microinjections of hcrt-1 (0.5-10 pmol) into the caudal lateral and medial subnuclei of the NTS complex of the alpha-chloralose of the urethane-anaesthetized E-treated OVX rat elicited a dose-related decrease in heart rate (HR). On the other hand, although a dose-response effect on arterial pressure was evident, significant arterial pressure responses were observed only at the higher dose of hcrt-1 (>2.5 pmol). In the OVX only female rat, microinjection of hcrt-1 into similar NTS sites elicited a bradycardia and depressor response only at the highest dose of hcrt-1, and these responses were significantly smaller in magnitude than those elicited in the OVX+E animal. In addition, in the OVX only animals, a few sites within the caudal commissural subnucleus of the NTS complex were found at which hcrt-1 elicited tachycardia and pressor responses. Finally, it was found that the reflex bradycardia to the activation of arterial baroreceptors as a result of increasing systemic arterial pressure with phenylephrine (2-4 microg/kg) was significantly potentiated in the OVX+E animals only. These data suggest that hcrt-1 in the NTS of the female activates a neuronal circuit that controls the circulation and that the circulating level of E alters the sensitivity of these cardiovascular circuits to hcrt-1.

Cardiac effects of hypocretin-1 in nucleus ambiguus

Although recent studies have reported hypocretin 1 (hcrt-1)-like-immunoreactivity (ir) within the region of the nucleus ambiguus (Amb) in the caudal brain stem, the function of hcrt-1 in the Amb on cardiovascular function is not known. Three series of experiments were done in male Wistar rats to investigate the effects of microinjections of hcrt-1 into Amb on heart rate (HR), mean arterial pressure (MAP), and the arterial baroreceptor reflex. In the first series, a detailed mapping of the distribution of hcrt-1- and hcrt-1 receptor (hcrtR-1)-like-ir was obtained of the Amb region. Although hcrt-1-like- and hcrtR-1-like-ir were found throughout the rostrocaudal extent of the Amb and adjacent ventrolateral medullary reticular formation, most of the hcrtR-1-like-ir was observed in the area just ventral to the compact formation of Amb, in the region of the external formation of the nucleus (Ambe). In the second series, the Amb region that contained hcrt-1 and hcrtR-1-ir was explored for sites that elicited changes in HR and MAP in urethane and alpha-chloralose-anesthetized rats. Microinjections of hcrt-1 (0.5-2.5 pmol) into the Ambe elicited a dose-related decrease in HR, with little or no direct change in MAP. The small decreases in MAP were found to be secondary to the HR changes. The largest bradycardia responses were elicited from sites in the Ambe. Administration (iv) of the muscarinic receptor antagonist atropine methyl bromide or ipsilateral vagotomy abolished the HR response, indicating that the HR response was due to activation of vagal cardiomotor neurons. In the final series, microinjections of hcrt-1 into the Ambe significantly potentiated the reflex bradycardia elicited by activation of the baroreflex as a result of the increased MAP after the intravenous injection of phenylephrine. These data suggest that hcrt-1 in the Ambe activates neuronal systems that alter the excitability of central circuits that reflexly control the circulation through the activation of vagal preganglionic cardioinhibitory neurons.

Cardiovascular effects of hypocretin-1 in nucleus of the solitary tract

Experiments were done in male Wistar rats to investigate the effects of microinjection of hypocretin-1 (Hcrt-1) into the nucleus of the solitary tract (NTS) on mean arterial pressure (MAP), heart rate (HR), and the baroreflex. In the first series, the distribution of Hcrt-1-like immunoreactivity (Ir) was mapped within the region of NTS. Hcrt-1 Ir was found throughout the NTS region, predominantly within the caudal dorsolateral (Slt), medial (Sm), and interstitial subnuclei of the NTS. In the second series, in alpha-chloralose or urethane-anesthetized rats, microinjection of Hcrt-1 (0.5-5 pmol) into the caudal NTS elicited a dose-dependent decrease in MAP and HR. A mapping of the caudal NTS region showed that the largest depressor and bradycardia responses elicited by Hcrt-1 were from sites in the Slt and Sm. In addition, doses >2.5 pmol at a small number of sites localized to the caudal commissural nucleus of NTS elicited pressor and tachycardia responses. Intravenous administration of the muscarinic receptor blocker atropine methyl bromide abolished the bradycardia response and attenuated the depressor response, whereas subsequent administration of the nicotinic receptor blocker hexamethonium bromide abolished the remaining MAP response. Finally, microinjection of Hcrt-1 into the NTS significantly potentiated the reflex bradycardia to activation of arterial baroreceptors as a result of increasing MAP by systemic injections of phenylephrine (2-4 microg/kg). These results suggest that Hcrt-1 in the NTS activates neuronal circuits that increases vagal activity to the heart, inhibits sympathetic activity to the heart and vasculature, and alters the excitability of NTS neuronal circuits that reflexly control the circulation.

Identification of neurons containing orexin-B (hypocretin-2) immunoreactivity in limbic structures

Orexins (hypocretins) are neuropeptides which have recently been identified exclusively within lateral hypothalamic and perifornical neurons, and these orexin (ox) containing neurons appear to have extensive projections to all levels of the neuraxis. In this study, we report the identification of two distinct clusters of neurons containing ox-B-like immunoreactivity within the amygdaloid complex of the rat. A cluster of small to medium size ovoid shaped neurons containing ox-B-like immunoreactivity was found predominantly within the lateral division of the central nucleus of the amygdala (ACe). A second distinct, but smaller group of ox-B labelled neurons with similar shapes and sizes to those in ACe was also identified in the anterior lateral subnucleus of the bed nucleus of the stria terminalis (BST) immediately adjacent the internal capsule, and in an area just ventral to the lateral ventricle. Neurons containing ox-A-like immunoreactivity were not observed in either structure. However, both structures contained ox-A- and ox-B labelled varicose fibers. Unilateral electrolytic lesions of the lateral hypothalamic area that contained ox-A and ox-B neurons did not alter the labelling of either ACe or BST ox-B pericarya. As both the ACe and BST are known to be involved in integrating complex homeostatic mechanisms associated with behaviours, these data suggest that a specific subset of ox-B neurons within the amygdaloid complex may serve as a component of neuronal circuits coordinating these responses.

Pontine sources of norepinephrine in the cat cochlear nucleus

In the current study, the distribution of noradrenergic neurons in the pontine tegmentum that project to the cochlear nucleus was determined with retrograde tract tracing combined with neurotransmitter immunohistochemistry in the cat. Double-labeled neurons were observed in all noradrenergic cell groups, in both the dorsolateral and the ventrolateral tegmentum. Half of the double-labeled cells were located in the locus coeruleus complex. Most of these were situated in its ventral division. Most other double-labeled cells were located in peribrachial regions, especially lateral to the brachium conjunctivum. Relatively few double-labeled cells were observed in both the A4 and the A5 cell groups, 2% and 0.4%, respectively, of the total. Except for neurons in A5, which projected only contralaterally, the projections were bilateral, with an ipsilateral preponderance. The results indicate that neurons located in the ipsilateral dorsolateral tegmentum, namely, in the locus coeruleus complex and the peribrachial region, are the primary source of pontine noradrenergic afferents to the cochlear nucleus of the cat.

Evidence that dopamine-beta-hydroxylase immunoreactive neurons in the lateral reticular nucleus project to the spinal cord in the rat

The existence of noradrenergic projections from the lateral reticular nucleus (LRt) to the dorsal quadrant of cervical, thoracic, or lumbar spinal cord was investigated using a combined method of WGA-apo-HRP-gold retrograde tracing and dopamine-beta-hydroxylase (DBH) immunocytochemistry. Preliminary retrograde tracing studies indicated that LRt neurons projecting to cervical, thoracic, or lumbar spinal cord were characteristically located near the perimeter of the LRt. Double-labeling experiments demonstrated that a portion of these peripherally-located, spinal-projecting neurons were DBH-immunoreactive. Double-labeled neurons were also located at the parvocellular division of the contralateral LRt in the thoracic injection cases. Double-labeled neurons were not observed at the subtrigeminal division in cervical, thoracic, or lumbar injection case. The results suggest the possibility that the noradrenergic LRt-spinal pathway might be involved in a variety of pain processing and cardiovascular regulatory functions in the rat.

Differential effects from parapyramidal region and rostral ventrolateral medulla mediated by substance P

Rostral ventrolateral medulla (rVLM) and parapyramidal region (PPr) serve as important medullary control sites for sympathoexcitation. rVLM and PPr have direct projections to the intermediolateral cell column (IML) that are thought to be important in maintaining mean arterial blood pressure (MAP). Substance P (SP) is found in PPr neurons and in and near the subretrofacial area of the rVLM. At least some of these cells project to the IML. We investigated the involvement of SP at the IML in mediating rVLM- and PPr-evoked pressor responses in the chloralose-anesthetized cat. Pressor responses to electrical and chemical PPr and rVLM stimulation were altered after intrathecal injection, at the level of the T1-T3 spinal cord, of either SP antagonist [D-Pro(2), D-Phe(7), D-Trp(9)]-SP, SP antagonist CP 96,345, or SP antiserum. Although MAP and heart rate responses to PPr stimulation were attenuated by intrathecal SP antagonists or antiserum, MAP responses to rVLM stimulation were augmented. Previous studies have revealed differences in transmitters associated with these two areas, even though the general response of both areas is sympathoexcitatory. The present study implies that the identical substance may increase or decrease the MAP response depending on the pathway activated.

Response of tracheal smooth muscle tone to lower brain stem hypoxia in dogs

We examined effects of central hypoxia on tracheal smooth muscle (TSM) tone, phrenic nerve activity (PNA) and blood pressure (BP) in decerebrated, paralysed, and artificially ventilated dogs. Central hypoxia was induced by injection of N2-saturated saline (5 ml; PO, 25-32 torr) through a catheter in the vertebral artery. The effects of central hypoxia were compared with the responses to central chemoreceptors stimulation, namely central hypercapnia induced by intravertebral injection of high CO2 saline (5 ml; PCO2 90-100 torr, PO2 80-120 torr, pH 7.38-7.42) buffered by HCO3-. Central hypoxia caused relaxation of TSM accompanied by depression of PNA and elevation of BP. In contrast, central hypercapnia evoked tracheal constriction along with respiratory excitation and pressor response. The tracheal relaxation in response to central hypoxia occurred with onset and peak latencies similar to those observed in PNA depression and BP elevation. This suggests a common source for the synaptic inputs to three distinct control systems involved in cardiovascular, respiratory and airway functions. Such neuronal substrate is considered to be activated by central hypoxia.

Association of spinal lamina I projections with brainstem catecholamine neurons in the monkey

In addition to giving primary projections to the parabrachial and periaqueductal gray regions, ascending lamina I projections course through and terminate in brainstem regions known to contain catecholaminergic cells. For this reason, double-labeling experiments were designed for analysis with light and electron microscopy. The lamina I projections in the Cynomolgus monkey were anterogradely labeled with Phaseolus vulgaris leucoagglutinin (PHA-L) and catecholamine-containing neurons were labeled immunocytochemically for tyrosine hydroxylase (TH). Light level double-labeling experiments revealed that the terminations of the lamina I ascending projections through the medulla and pons strongly overlap with the localization of catecholamine cells in: the entire rostrocaudal extent of the ventrolateral medulla (A1 caudally, C1 rostrally); the solitary nucleus and the dorsomedial medullary reticular formation (A2 caudally, C2 rostrally); the ventrolateral pons (A5); the locus coeruleus (A6); and the subcoerulear region, the Kölliker-Fuse nucleus, and the medial and lateral parabrachial nuclei (A7). At the light microscopic level, close appositions between PHA-L-labeled lamina I terminal varicosities and TH-positive dendrites and somata were observed, particularly in the A1, A5 and the A7 cell groups on the contralateral side. At the electron microscopic level, examples of lamina I terminals were found synapsing on cells of the ventrolateral catecholamine cell groups in preliminary studies. The afferent input relayed by these lamina I projections could provide information about pain, temperature, and metabolic state as described previously. Lamina I input could impact interactions of the catecholamine system with higher brain centers modulating complex autonomic, endocrine, sensory, motor, limbic and cortical functions such as memory and learning. Nociceptive lamina I input to catecholamine cell regions with projections back to the spinal cord could form a feedback loop for control of spinal sensory, autonomic and motor activity.

[3H]Nisoxetine binding sites in the cat brain: an autoradiographic study

The binding of [3H]nisoxetine, a selective inhibitor of the high-affinity noradrenaline uptake sites, was studied on frontal frozen sections of the cat brain. The highest densities in autoradiographic signal were observed in the nucleus locus coeruleus and its ascending pathways, in the area postrema and in the dorsal part of the inferior olive, the pontine nuclei, the raphe nuclei, the colliculi, the periventricular and lateral areas of the hypothalamus, the suprachiasmatic nucleus, the nucleus accumbens and the olfactory bulb. A moderately high concentration of binding sites was observed in the hippocampal formation, especially in the molecular layer of Ammon's horn, in the superficial layers of the entorhinal cortex and in the indusium griseum. Binding sites were visualized in all the subdivisions of the neocortex. The highest density of binding was generally detected in the outer edge of the superficial layer I. In some cortical areas, especially in the visual cortex, labeling with a prevalent laminar distribution in the superficial layers I-III and in the deep layers V-VI was clearly observed. Moderate to low densities of binding sites were seen in most other areas of the brain except in the white matter, the caudate nucleus and putamen, which were devoid of labeling. Overall these findings indicate a good correlation between the distribution of [3H]nisoxetine binding sites and the noradrenergic systems. Furthermore, data suggest that in several areas, high-affinity noradrenaline reuptake mechanisms could play an important role in local interactions between the noradrenergic system and the other monoaminergic systems.

Distribution of brainstem projections from spinal lamina I neurons in the cat and the monkey

The distribution of terminal projections in the brainstem from lamina I neurons in the spinal dorsal horn was investigated with the anterograde tracer Phaseolus vulgaris-leucoagglutinin in the cat and the cynomolgus monkey. Iontophoretic injections made with physiological guidance were restricted to lamina I or to laminae I-III in the cervical (C6-8) or lumbar (L6-7) enlargement. The distribution of terminal labeling was essentially identical in the cat and the monkey, although consistently of greater intensity in the monkey. Terminations were observed in the solitary nucleus, the dorsomedial medullary reticular formation, the entire rostrocaudal extent of the ventrolateral medulla, the locus coeruleus, the subcoerulear region and the Kölliker-Fuse nucleus, the lateral and medial portions of the parabrachial nucleus, the cuneiform nucleus, the ventrolateral and lateral portions of the periaqueductal gray, and the intercollicular nucleus. Lamina I terminations were generally bilateral in the medulla but more dense contralaterally in the pons and mesencephalon. The density and laterality of labeling in the medulla varied between cases independently from that in the pons and mesencephalon, suggesting that the lamina I projections to these regions may originate from different subsets of neurons. A clear topographic organization was observed only in the lateral column of the periaqueductal gray, where lumbar lamina I terminations were found caudal to cervical terminations. These observations indicate that spinal lamina I neurons project to a variety of brainstem sites involved in autonomic (cardiovascular, respiratory) and homeostatic processing and the control of behavioral state. These projections provide an afferent substrate for spino-bulbo-spinal somatoautonomic reflex arcs activated by nociceptive, thermoreceptive activity and for a spino-bulbo-hypothalamic relay of such activity by cells in the caudal ventrolateral medulla. These observations support the general concept that lamina I projections distribute modality-selective sensory information relevant to the physiological status and maintenance of the tissues and organs of the entire organism.

Human intermediate reticular zone: a cyto- and chemoarchitectonic study

The primary aim of this study was to provide a comprehensive account of the morphology, topography, and frequency of tyrosine hydroxylase- and substance P-like (TH-LI, SP-LI) immunoreactive neurons of the human intermediate reticular zone (IRt), the putative autonomic zone of the medullary reticular formation. A further aim is to examine the IRt from a three-dimensional perspective using computer reconstruction techniques and compare its relationship with other structures in the rest of the medullary reticular formation. Six adult human brains were obtained from individuals with no sign of cerebral disease and were perfusion fixed. Free-floating transverse sections were immunostained with monoclonal antibodies against tyrosine hydroxylase and substance P by the avidin-biotin-peroxidase technique. The entire IRt displays TH-LI cell bodies and fibers, and thus it is readily distinguishable from the neighbouring gigantocellular and parvicellular reticular nuclei. In contrast, SP-LI cells are restricted to the external part of the IRt that is found in the open medulla, while SP-LI fibers are more widely distributed. The IRt displays TH-LI neurons which are fusiform, oval, and round in shape. The SP-LI neurons of the IRt are primarily oval and fusiform. In preparations stained for Nissl substance, IRt cells were classified as pigmented and nonpigmented. A characteristic feature of the IRt is that its cells are larger (20 +/- 4 micrograms) than those of the laterally adjoining parvicellular (12 +/- 2 micrograms) and clearly smaller than those of the medially adjoining gigantocellular nuclei (33 +/- 6 micrograms). The shape of the IRt is in keeping with the radial organization of the medulla with zones emanating from the fourth ventricle. Three-dimensional computer reconstructions of the cell plots show that 1) TH-LI neurons extend through the entire IRt and densely packed in the rostral part of the ventrolateral IRt and 2) SP-LI neurons are found only in the rostral half of the medulla oblongata.

Collateral axonal projections from ventrolateral medullary non-catecholaminergic neurons to central nucleus of the amygdala

Retrograde tract-tracing techniques were used to investigate whether catecholaminergic neurons in the ventrolateral medulla (VLM) send collateral axonal projections to both central nuclei of the amygdala (ACe) in the rat. Rhodamine-labelled latex microspheres or fluorogold (2%) were microinjected into the region of either the right or left ACe. After a survival period of 10-12 days, the rats were sacrificed and transverse sections of the brainstem were processed immunohistochemically for the identification of cell bodies containing the catecholamine biosynthetic enzymes tyrosine hydroxylase (TH) or phenylethanolamine-N-methyltransferase (PNMT). Neuronal perikarya containing the retrogradely transported tracers were observed throughout the rostrocaudal extent of VLM, bilaterally. Approximately 10% of the retrogradely labelled neurons were observed to contain both retrograde tracers. The majority (79 +/- 6.8%) of these double labelled neurons were located within the caudal VLM and their number decreased rostrally. In addition, the proportion of double labelled neurons to single labelled neurons in VLM decreased rostrally; approximately 11% in the caudal VLM and 6% in the rostral VLM. Furthermore, approximately 21% of all VLM neurons that projected to ACe were found to be catecholaminergic: 75% of these were immunoreactive to TH and 25% to PNMT. However, no neurons were found in VLM that contained both retrograde tracers and immunoreactivity to TH or PNMT. These data demonstrate that axons originating from non-catecholaminergic neurons in VLM bifurcate to innervate ACe bilaterally. Although the function of these VLM neurons that project to both ACe is not known, they may be the anatomical substrate by which VLM neurons relay simultaneously autonomic and/or visceral sensory information to influence the activity of ACe.

Adrenergic cell group in rostral ventrolateral medulla of cat: its correlation with central chemoreceptors

We have proposed a hypothesis that secondary neurons mediating central respiratory chemoreception are not restricted to the medullary superficial layer. This idea was further examined in the present physiological and morphological studies. We identified the 'S' area, i.e. the medullary surface area where cold blockade produced apnea, in anesthetized, spontaneously breathing cat. We then evaluated how the apnea was modified by injection of CO2-saturated saline into the vertebral-basilar artery. The CO2 injection caused immediate reappearance of respiratory rhythm, although intensity of inspiratory activity was smaller than in the control. This incomplete recovery suggests that the responsive structure extends deeply below the surface. The extent of the cell group underlying the 'S' area was evaluated by morphological study. Medullary transverse sections including the 'S' area were treated with three distinct antisera against phenylethanolamine N-methyltransferase (PNMT), dopamine-beta-hydroxylase (DBH), and 5-hydroxytryptamine (5-HT). The PNMT-labelled cell group was found to exactly underlie the 'S' area, although the DBH- and the 5-HT-labelled cell groups did not show close topographic correlation with the 'S' area. PNMT cells were located in the region ventral to retrofacial nucleus within 0.5-1.5 mm depth beneath the surface. These results suggest that adrenergic cells in the rostral ventrolateral medulla are important candidates for secondary neurons mediating central respiratory chemoreception.

Collateral axonal projections to limbic structures from ventrolateral medullary A1 noradrenergic neurons

Experiments were done to investigate whether catecholaminergic neurons within the ventrolateral medulla (VLM) send collateral axonal projections to the central nucleus of the amygdala (ACe) and the bed nucleus of the stria terminalis (BST). Unilateral microinjections of the fluorescent retrograde tracers fluorogold (FG) or rhodamine labelled latex micro-beads (Rd) were made into either ACe or BST in the rat. Brainstem sections were then processed immunohistochemically for the identification of cell bodies containing the catecholamine biosynthetic enzymes tyrosine hydroxylase, dopamine beta-hydroxylase (DBH) or phenylethanolamine-N-methyltransferase (PNMT). Retrogradely labelled cell bodies projecting to either ACe or BST were found throughout the rostrocaudal extent of VLM, bilaterally. Approximately 44% of these retrogradely labelled neurons were found to contain both retrograde tracers. In addition, approximately 91% of the VLM neurons that send collateral axonal projections to ACe and BST were also immunoreactive to DBH. None were found to contain PNMT immunoreactivity. These results demonstrate that noradrenergic neurons of the A1 cell group in VLM innervate ACe and BST via collateral axonal projections and suggest that these VLM neurons may be directly involved in relaying cardiovascular afferent and/or visceral afferent information directly to these limbic structures.

Distribution of tachykinin- and opioid-expressing neurons in the hamster solitary nucleus: an immuno- and in situ hybridization histochemical study

In several sensory systems, tachykinin- and opioid-expressing neurons functionally interact and influence the processing of afferent information. To determine whether a similar relationship exists for the processing of general and special (gustatory) visceral afferent information, the present study mapped the distributions of these two neuronal phenotypes within the nucleus of the solitary tract (NST) of the hamster by employing a combination of immuno- and in situ hybridization histochemistry (ISHH). The hamster was chosen because it is frequently used as a model in taste studies, yet there is a relative dearth of data about peptide expression or the classical neurotransmitters in the brainstem of this animal. The immunohistochemical analyses employed 2 highly selective antisera directed towards the prototypical tachykinin and opioid peptides, i.e. substance P (SP) and methionine enkephalin (ENK), respectively. Intense staining of fibers and preterminal/terminal puncta was concentrated in the rostral pole or gustatory zone of the NST. SP-, but not ENK-like immunoreactivity was also observed in long courses of axon bundles traversing the brainstem enroute to the NST. Local application of colchicine engendered the appearance of a moderate number of SP-positive somata that were mostly clustered in the medial, central and intermediate subnuclei, as well as being scattered throughout the remainder of the NST, including the gustatory zone. A low number of isolated ENK-positive somata were also observed throughout the NST. The somal areas of the SP- and ENK-positive somata averaged 86.3 and 81.8 microns 2, respectively. The ISHH studies were performed using 2 selective oligodeoxynucleotide probes with complementary sequences to mRNAs encoding gamma-preprotachykinin (PPT) and preproenkephalin (PPE) molecules. Overall, the cellular expression of PPT mRNA within the NST corresponded both in distribution and in number to those identified by immunohistochemical analyses using anti-SP serum. In contrast, ISHH analyses monitored a significantly greater number of PPE-expressing somata in the medial, central, intermediate and ventrolateral nuclei than were ENK immunoreactive. These findings indicate that tachykinin and opioid peptide phenotypes are represented in neurons throughout the hamster NST and suggest a functional role for PPT- and PPE-related peptide forms in the modulation of afferent general visceral and gustatory information.

Innervation of the amygdaloid complex by catecholaminergic cell groups of the ventrolateral medulla

The projections to the amygdaloid complex (AMG), originating in the catecholaminergic cell groups of the ventrolateral medulla (VLM), were studied in the rat by using either the retrograde tracer fluoro-gold (FG) or the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in combination with tyrosine hydroxylase (TH) and/or phenylethanolamine-N-methyltransferase (PNMT) immunohistochemistry. In the first series of experiments, injections of FG were made into regions of the central nucleus of the amygdala (ACe) where dense TH and PNMT immunoreactivity was previously observed, and then sections of the brainstem were processed for TH and PNMT immunoreactivity. FG retrogradely labelled neuronal cell bodies were observed throughout the rostrocaudal extent of VLM, bilaterally, with a contralateral predominance. Approximately 44% of the FG labelled cell bodies in VLM were also immunoreactive to the catecholamine biosynthetic enzymes TH and/or PNMT. Most of these catecholaminergic neurons were part of the A1 noradrenergic cell group in the caudal VLM and to a lesser extent part of the C1 adrenergic cell group in the rostral VLM. In the second series of experiments, PHA-L was iontophoresed into VLM at different rostrocaudal levels where in the previous series of experiments FG retrogradely labelled cell bodies were observed. Transverse sections of the forebrain and brainstem were then processed for the demonstration of PHA-L and either TH or PNMT immunoreactivity in cell bodies, axons, and presumptive axon terminals. PHA-L injection sites within either the caudal or rostral VLM resulted in labelled axons and terminal bouton-like swellings primarily in the contralateral AMG and to a lesser extent in the ipsilateral AMG. The ACe was observed to receive the greatest innervation from either VLM site. Additionally, PHA-L labelled fibers and presumptive terminal boutons were observed within the intercalated, medial, basomedial, and basolateral nuclei of the AMG. Most of the PHA-L labelled fibers and presumptive terminal boutons in the AMG after a caudal VLM (A1 region) injection also displayed TH immunoreactivity, whereas after a PHA-L injection into the rostral VLM (C1 region) all of the labelled axons and axon terminals in the AMG also were immunoreactive to PNMT. These data demonstrate that catecholaminergic neurons in A1 and C1 regions of VLM innervate the AMG and suggest that these VLM neurons may be involved in relaying afferent information directly to the AMG which influences the activity of AMG neurons controlling autonomic, endocrine, and behavioural functions.

Distribution of dopamine-containing neurons and fibres in the feline medulla oblongata: a comparative study using catecholamine-synthesizing enzyme and dopamine immunohistochemistry

The distribution of dopamine-immunoreactive neurons and fibres in the feline medulla oblongata was examined by immunocytochemistry with antisera to the catecholamine-synthesizing enzymes tyrosine hydroxylase, dopamine-beta-hydroxylase and phenylethanolamine-N-methyltransferase, and with antisera to the catecholamines dopamine and L-dihydroxyphenylalanine. Neurons immunoreactive for the catecholamine-synthesizing enzymes were found in two regions of the medulla, the ventrolateral A1 region and the dorsomedial A2 region. Double-staining studies with antisera to the enzymes indicated that a population of neurons within both regions were immunoreactive for tyrosine hydroxylase but not dopamine-beta-hydroxylase or phenylethanolamine-N-methyltransferase, implying that they synthesize dopamine. Studies using the dopamine antisera demonstrated the presence of dopamine-immunoreactive neurons in both the ventrolateral and dorsomedial regions of the medulla; in the dorsomedial region, they were found in the area postrema, nucleus tractus solitarius and dorsal motor vagal nucleus, mainly at levels caudal to the obex. Dopamine-immunoreactive fibres were found in several areas of the medulla including the nucleus tractus solitarius, inferior olive, dorsal motor vagal, spinal trigeminal, hypoglossal, cuneate, gracile, and raphe nuclei. Double-staining studies with antisera to dopamine and dopamine-beta-hydroxylase revealed a population of cells immunoreactive for dopamine alone. The presence of some double-stained neurons, however, implies some cross-reactivity of the dopamine antiserum with noradrenaline or adrenaline and/or recognition of dopamine present as a metabolic intermediary in some noradrenergic neurons. No L-dihydroxyphenylalanine-immunoreactive neurons were found in the medulla, although fibres were seen. These data provide evidence for the existence of catecholamine neurons which utilize dopamine as a final synthetic product within the medulla oblongata.

Adrenergic projections from the lower brainstem to the hypothalamic paraventricular nucleus, the lateral hypothalamic area and the central nucleus of the amygdala in rats

Fine networks of phenylethanolamine N-methyltransferase (PNMT)-immunoreactive fibers are found in the hypothalamic paraventricular nucleus--mainly in the anterior, dorsal and dorso-medial parvicellular subdivisions, the lateral hypothalamus (dorsal, lateral and ventral to the fornix) and in the central amygdaloid nucleus. Coronal hemisections of the brainstem through the rostral level of the medulla oblongata show that most hypothalamic and amygdaloid PNMT fibers arise from the medullary adrenergic cell groups. Fourteen, but not 10 days after total hemisections, PNMT fibers disappeared almost completely from the hypothalamus and amygdala, ipsilateral to the knife cuts. A small decrease was also observed in the ventral, lateral hypothalamus on the contralateral side. Partial depletion of PNMT-immunoreactivity in the hypothalamus and the amygdala after medial or lateral brainstem hemisections indicates that ascending PNMT-immunoreactive fibers pass through mainly the lateral portion of the medulla, but some fibers also in its medial portion. Midsagittal transection of the diencephalon slightly reduced PNMT immunostaining in the paraventricular nucleus and the lateral hypothalamus bilaterally. The results show that the ascending PNMT system essentially is ipsilateral, but probably with a small crossing-over component, both at the diencephalic and lower brainstem level.

Rostrocaudal differences in morphology and neurotransmitter content of cells in the subretrofacial vasomotor nucleus

The rostral ventrolateral medulla (RVLM) contains sympathoexcitatory neurons that exert a powerful control over the sympathetic outflow to the cardiovascular system. In the cat there is a concentration of such neurons (but not neurons subserving other functions) within a narrow longitudinal column in the RVLM termed the subretrofacial (SRF) nucleus. Furthermore, it has been suggested that there are subgroups of cells, located at different rostrocaudal levels of the SRF nucleus, that preferentially or exclusively control different vascular beds (e.g. in the kidney and hindlimb). The aim of this study was to map quantitatively the rostrocaudal distribution within the nucleus of different cell types, defined according to morphological and/or chemical criteria, and to correlate this with the regional vasomotor effects (in hindlimb and kidney) evoked by stimulation of SRF cells at the corresponding rostrocaudal levels. SRF cells were highly heterogeneous with respect to both their morphology and chemical properties. They varied greatly in size (equivalent diameter ranging from 10-40 microns) as well as in shape and orientation. An immunohistochemical examination using the avidin-biotin procedure revealed that many SRF cells (estimated 57% of all SRF cells) were immunoreactive for tyrosine hydroxylase (TH, a marker of catecholamine cells). In addition, there were SRF cells immunoreactive for neuropeptide Y (NPY, 11% of total), enkephalin (ENK, 16% of total), and serotonin (5HT, 10% of total), but not for substance P, galanin or somatostatin. Different cell types, defined according to their morphology and/or chemical properties, were unevenly distributed throughout the nucleus. In the most caudal part of the SRF nucleus, virtually all cells were TH-positive, and the large majority (estimated 80%) were NPY-positive, suggesting that many cells at this level contained both TH and NPY. In contrast, in the most rostral part of the SRF nucleus, only 30% of cells were TH-positive, and no NPY-positive cells were observed. Both 5HT- and ENK-positive cells were found throughout the rostrocaudal extent of the nucleus, but predominantly within its rostral part. Furthermore, TH-positive cells in the rostral SRF nucleus were on average significantly larger (mean equivalent diameter 18-43% greater) than TH/NPY-positive cells in the caudal part of the nucleus, but smaller than 5HT- or ENK-positive cells at the same level. Overall, rostral cells (regardless of their chemical type) were larger than caudal cells within the SRF nucleus (mean equivalent diameter 13-28% greater).(ABSTRACT TRUNCATED AT 400 WORDS)

Caudal ventrolateral medullary projections to the nucleus of the solitary tract in the cat

The projections of neurons, in and around the A1 noradrenergic cell group of the caudal ventrolateral medulla (VLM), to nucleus of the solitary tract (NTS) were studied in the cat using the anterograde transport of Phaseolus vulgaris leucoagglutinin (PHA-L). PHA-L was micro-iontophoresed into the region of the A1 noradrenergic cell group and after a 7-17 day survival period animals were sacrificed and brainstem sections were processed for PHA-L or tyrosine hydroxylase (TH) immunoreactivity. PHA-L injections within the region of the A1 cell group resulted in labelled fibers with their presumptive terminal boutons primarily in the ipsilateral commissural and medial subnuclei of NTS. A light projection to the ipsilateral parvocellular lateral and ventrolateral subnuclei of the NTS complex was also observed. These data demonstrate that neurons in the region of the A1 noradrenergic cell group project to regions of NTS that receive cardiovascular afferent inputs and suggest that VLM may influence the activity of neurons in NTS involved in the reflex regulation of the circulation.

Cardiorespiratory responses to chemical stimulation of the caudal most ventrolateral medulla in the cat

Chemical stimulation of caudal ventrolateral medulla evoked both pressor and depressor responses. The pressor sites were generally located caudal to depressor sites. Effects on heart rate were variable. Significant increases in minute ventilation were also observed, which were primarily due to changes in respiratory frequency.

Strain difference in phenylethanolamine N-methyltransferase activity and immunoreactivity of medulla oblongata of Sprague-Dawley and Long-Evans hooded rats

Previously, we reported that retinal phenylethanolamine N-methyltransferase (PNMT) activity of Sprague-Dawley (SD) rats was significantly higher than that of Long-Evans (LE) hooded rats. However, there were no noticeable differences observed in PNMT-immunostaining patterns between the retinae of LE and SD rats. In order to examine this discrepancy, we extended this study to areas of the medulla oblongata harboring PNMT-containing cell bodies. In the present report, we demonstrate that the enzyme activity as well as the immunoreactivity of PNMT in medulla oblongata of SD rats were significantly higher than that observed in the LE strain.

A comparative analysis of neurons containing catecholamine-synthesizing enzymes and neuropeptide Y in the ventrolateral medulla of rats, guinea-pigs and cats

Neurons in the ventrolateral medulla oblongata of rats, guinea-pigs and cats that contain tyrosine hydroxylase, dopamine-beta-hydroxylase, phenylethanolamine-N-methyltransferase and neuropeptide Y have been demonstrated immunohistochemically in serial coronal sections of tissue taken from the level of the cervical spinal cord to the level of the facial nucleus. The anatomical distribution of these neurons has been described, quantified and reconstructed in three dimensions to compare the neuron populations between species. In all species, between 50 and 90% of immunoreactive neurons lay rostral to the level of the obex. There were no significant differences in the number and distribution of neurons containing catecholamine-synthesizing enzymes between control animals and those pretreated with colchicine, with two exceptions: all dopamine-beta-hydroxylase neurons were weakly immunoreactive without colchicine pretreatment in cats, and pretreatment with colchicine revealed a small rostral group of tyrosine hydroxylase-positive neurons in guinea-pigs. There were remarkable similarities in the rostrocaudal distributions of neurons containing tyrosine hydroxylase, dopamine-beta-hydroxylase and neuropeptide Y in relation to comparable anatomical landmarks across the species. However, the distributions of neurons containing tyrosine hydroxylase. Phenylethanolamine-N-methyltransferase-positive neurons, while densely stained in rats, were only faintly stained in cats and absent in guinea-pigs; the distribution of these neurons was similar to the distribution of neurons containing only tyrosine hydroxylase. The similarity of the distribution of neurons demonstrated using tyrosine hydroxylase, dopamine-beta-hydroxylase and neuropeptide Y immunohistochemistry implies that homologous catecholamine-containing neuron groups do exist in the ventrolateral medulla despite the variation in phenylethanolamine-N-methyltransferase between species. In contrast to the previous classification of neuron groups into A1 and C1 based on the presence or absence of this latter enzyme, the data suggest that a discrete group of tyrosine hydroxylase-immunoreactive neurons, which probably do not contain dopamine-beta-hydroxylase or neuropeptide Y, can be distinguished in the rostral ventrolateral medulla of all species. The absence of detectable dopamine-beta-hydroxylase in this group of neurons suggests that they may not synthesize either adrenaline or noradrenaline.

Four groups of tyrosine hydroxylase-immunoreactive neurons in the ventrolateral medulla of rats, guinea-pigs and cats identified on the basis of chemistry, topography and morphology

The data in the preceding paper [Halliday G. M. and McLachlan E. M. (1991) Neuroscience 43, 531-550] suggest that some neurons in the rostral ventrolateral medulla contain some catecholamine-synthesizing enzymes but may not produce catecholamines. The present study addresses this question directly by comparing the anatomical location and morphology of these neurons with those revealed by formaldehyde-induced fluorescence. Catecholamine-containing somata of rats and guinea-pigs have been demonstrated following FAGLU-perfusion in normal untreated animals, in animals pretreated with pargyline (a monoamine oxidase inhibitor), and in animals pretreated with colchicine (to block axoplasmic transport). The number and location of fluorescent somata in the ventrolateral medulla have been determined in serial coronal sections of tissue from the cervical spinal cord to the level of the facial nucleus. Catecholamine-fluorescent neurons at different levels of the ventrolateral medulla varied in their topography and sensitivity to pharmacological manipulation. However, the rostrocaudal distributions in rats and guinea-pigs were quantitatively remarkably similar implying that homologous groups of catecholamine-containing neurons exist. Comparison between these distributions and those of somata stained immunohistochemically for catecholamine-synthesizing enzymes and neuropeptide Y [Halliday G. M. and McLachlan E. M. (1991) Neuroscience 43, 531-550] revealed that the majority of fluorescent neurons in both species probably contain dopamine-beta-hydroxylase and neuropeptide Y as well as tyrosine hydroxylase. Those neurons lying just caudal to the facial nucleus immunoreactive for tyrosine hydroxylase and phenylethanolamine-N-methyltransferase but not dopamine-beta-hydroxylase and neuropeptide Y also lack catecholamine fluorescence. This rostral group of somata can be identified immunohistochemically in cats. The size and morphology of catecholamine-fluorescent neurons have been analysed in detail, and compared with the same features of the immunohistochemically stained neurons. Three morphological types of catecholamine-containing neurons could be distinguished in material prepared by both techniques from rats and guinea-pigs, and in immunohistochemical material from cats. Rostral tyrosine hydroxylase-positive neurons, which differed morphologically from these three types, were present in all three species. On the basis of anatomical location, neuronal morphology and chemical characteristics, four groups of tyrosine hydroxylase-immunoreactive neurons have been identified in the ventrolateral medulla of rats, guinea-pigs and cats. Only the caudal three of these four groups appear to synthesize catecholamine, probably noradrenaline. From published data it seems likely that these four groups of tyrosine hydroxylase-positive neurons have distinct projections and functions related to cardiovascular and respiratory control.

Aromatic L-amino acid decarboxylase-immunohistochemistry in the cat lower brainstem and midbrain

By indirect immunohistochemistry, the present study examined the distribution of neuronal structures in the cat medulla oblongata, pons, and midbrain, showing immunoreactivity to aromatic L-amino acid decarboxylase (AADC), which catalyzes the conversion of L-3, 4-dihydroxyphenylalanine (L-DOPA) to dopamine, and 5-hydroxytryptophan to serotonin (5HT). With simultaneous and serial double immunostaining techniques, immunoreactivity to this enzyme was demonstrated in most of the catecholaminergic and serotonergic neurons. We could also demonstrate AADC-IR cell bodies that do not contain tyrosine hydroxylase (TH-) or 5HT-immunoreactivity (called "D-type cells") outside such monoaminergic cell systems. At the medullo-spinal junction, very small D-type cells were found within and beneath the ependymal layer of the 10th area of Rexed surrounding the central canal. D-type cells were localized in the caudal reticular formation, nucleus of the solitary tract, a dorsal aspect of the lateral parabrachial nucleus, and pretectal areas as have been reported in the rat. Furthermore, the present study describes, in the cat brainstem, new additional D-type cell groups that have not been reported in the rat. Dense or loose clusters of D-type cells were localized in the external edge of the laminar trigeminal nucleus, dorsal motor nucleus of the vagus, external cuneate nucleus, nucleus praepositus hypoglossi, central, pontine, and periaqueductal gray, superficial layer of the superior colliculus, and area medial to the retroflexus. D-type cells were loosely clustered in the lateral part of the central tegmental field dorsal to the substantia nigra, extending dorsally in the medial division of the posterior complex of the thalamus and medial side of the brachium of the inferior colliculus. They extended farther rostrodorsally along the medial side of the nucleus limitans and joined with the pretectal cell group. Almost all these cells were very small and ovoid to round with 1-2 short processes with the exception of dorsal motor vagal cells. AADC-IR axons were clearly identified in the vagal efferent nerves, longitudinal medullary pathway, dorsal tegmental bundle rostral to the locus coeruleus. Serotonergic axons were identified not only in the central tegmentum field and lateral side of the central superior nucleus, but also in the ventral surface of the medulla oblongata. We describe principal densely stained fiber plexuses in the cat brainstem. The findings of the present study provide a morphological basis for neurons that decarboxylate endogenous and exogenous L-DOPA, 5HTP, and other aromatic L-amino acids.

Localization of tyrosine hydroxylase and phenylethanolamine N-methyltransferase immunoreactive cells in the medulla of the dog

The tyrosine hydroxylase (TH)- and phenylethanolamine N-methyltransferase (PNMT)-immunoreactive cells of the medulla are closely associated with cardiovascular control in both the cat and rat. Although it is often the species of choice for cardiovascular studies, no previous study had characterized these cell groups in the dog. The TH- and PNMT-immunoreactive cells of the dog were distributed much as they are in both cat and rat but with some species variations, which may be indicative of their functional role.

Catecholamine-containing neurons in the sheep brainstem and diencephalon: immunohistochemical study with tyrosine hydroxylase (TH) and dopamine-beta-hydroxylase (DBH) antibodies

The present study describes the distribution and morphological characteristics of neurons and nerve fibers containing the catecholamine-synthesizing enzymes, tyrosine hydroxylase and dopamine-beta-hydroxylase, in the sheep brainstem and diencephalon on the basis of immunohistochemical procedures. Neurons and fibers were considered to be dopaminergic if they showed anti-tyrosine hydroxylase immunoreactivity, without corresponding anti-dopamine-beta-hydroxylase immunoreactivity. The structures labeled with both antisera were considered noradrenergic or adrenergic. The distribution of catecholaminergic neurons corresponds to that described by other authors with similar methods in the rat and in primates. The noradrenergic neurons belong to cell groups A1 to A7 and the dopaminergic neurons to cell groups A8 to A15. In almost all studied areas, the catecholaminergic innervation is similar to that observed in the other species. However, the central catecholaminergic systems of the sheep showed some specific characteristics: (1) groups A3 and A4, described in the rat, were not found, (2) group A14 contains fewer neurons than in the rat, (3) group A15 does not contain a dorsal but only a ventral portion, (4) there is a larger dispersion of neurons within each group, especially A6 and A7, than in rodents, and (5) there is a larger noradrenergic innervation of the catecholaminergic groups than in the other species.

Distribution of phenylethanolamine N-methyltransferase cell bodies, axons, and terminals in monkey brainstem: an immunohistochemical mapping study

Adrenaline (epinephrine) is an important candidate transmitter in descending spinal control systems. To date intrinsic spinal adrenergic neurons have not been reported; thus adrenergic input is presumably derived from brainstem sites. In this regard, the localization of adrenergic neurons in the brainstem is an important consideration. Maps of adrenergic cell bodies and to a lesser extent axons and terminal fields have been made in various species, but not in monkeys. Thus, the present study concerns the organization of adrenergic systems in the brainstem of a monkey (Macaca fascicularis) immunohistochemically mapped by means of an antibody to the enzyme phenylethanolamine N-methyltransferase (PNMT). PNMT-immunostained cell bodies are distributed throughout the medulla in two principal locations. One concentration of labeled cells is in the dorsomedial medulla and includes the nucleus of the solitary tract (NTS), the dorsal motor nucleus of the vagus (X), and an area ventral to X in a region of the reticular formation (RF) known as the central nucleus dorsalis (CnD) of the medulla. A few scattered cells are observed in the periventricular gray just ventral to the IVth ventricle and on midline in the raphe. The second major concentration of PNMT-immunostained cells is located in the ventrolateral RF, lateral and dorsolateral to the inferior olive (IO), including some cells in the rostral part of the lateral reticular nucleus (LRN). Terminal fields are located in the NTS, X, area postrema (AP), and the floor of the IVth ventricle in the medulla and pons. A light terminal field is also observed in the raphe, particularly raphe pallidus (RP). A heavy terminal field is present in locus coeruleus (LC). Fibers labeled for PNMT form two major fiber tracts. One is in the dorsomedial RF extending as a well-organized bundle through the medulla, pons, and midbrain. A second tract is located on the ventrolateral edge of the medulla and caudal pons. Fibers in this tract appear to descend to the spinal cord. A comparison with maps of other catecholamine neurons in primates is discussed, confirming that the distribution of the adrenergic system in monkeys is similar to that described in the human.

Distribution of noradrenaline immunoreactivity in the forebrain and midbrain of the lizard Gekko gecko

The distribution of noradrenaline (NA) immunoreactivity in the forebrain and midbrain of the lizard Gekko gecko was studied by means of recently developed antibodies against NA. Noradrenaline-containing cell bodies are found in the hypothalamic periventricular organ and ependymal wall of the infundibular recess of the diencephalon. They are also present in the locus coeruleus and the nucleus of the solitary tract of the brainstem. Noradrenaline-immunoreactive (NAi) fibers and varicosities are widely, but not uniformly, distributed throughout the forebrain and midbrain. In the telencephalon, dense plexuses of NAi fibers are found in the bed nucleus of the medial forebrain bundle, the vertical limb of the nucleus of the diagonal band of Broca, and the caudoventral part of the septal region. The diencephalon, the periventricular preoptic area, the supraoptic nucleus, and, in particular, the medial habenular nucleus are densely innervated by NAi fibers, whereas in the midbrain NAi plexuses are found in the ventral tegmental area, the substantia nigra and its dorsolateral extension (RA8), and in an area ventral to the nucleus interpeduncularis, pars ventralis. Moderately dense plexuses of NAi fibers are found in the small-celled medial cortex, the dorsal cortex, and the midbrain tectum. The remaining forebrain and midbrain areas are generally not or only sparsely innervated by NAi fibers. The distribution of NAi cell bodies and fibers resembles the pattern revealed with antibodies against dopamine-beta-hydroxylase (DBH). A remarkable exception is that the cells in the hypothalamic periventricular organ and ependymal wall of the infundibular recess are immunonegative for DBH. Possible explanations for this discrepancy are discussed. The present study on the distribution of NA immunoreactivity in the brain of Gekko gecko combined with the results of a previous report on the distribution of dopamine in the same species (Smeets et al., '86b) offer the opportunity to differentiate between the two catecholamines in the brain of this vertebrate.

Organization of ventrolateral medullary afferents to the hypothalamus

In summary, these anatomical and electrophysiological data have provided evidence to support the suggestion that VLM neurons project directly to regions of the hypothalamus that contain magnocellular neurosecretory neurons. In addition, these results support the suggestion that pathways ascending from the VLM to the hypothalamus function, in part, in the control of the release of the neurohypophyseal hormones by PVH and SON magnocellular neurosecretory neurons during activation of peripheral cardiovascular receptors.

Electrophysiological characterization of putative C1 adrenergic neurons in the rat

Recent studies in the rat have demonstrated that at least two populations of sympathoexcitatory reticulospinal neurons reside in the nucleus reticularis rostroventrolateralis. It appears that only one of these populations consists of C1 adrenergic neurons. The present study used both double-labeling (one retrograde tracer and immunohistochemistry) and triple-labeling (two retrograde tracers and immunohistochemistry) to determine if C1 adrenergic neurons, which are immunoreactive for phenylethanolamine N-methyltransferase, exhibit a projection pattern that is sufficiently unique to permit the electrophysiological discrimination between C1 adrenergic and non-adrenergic neurons in the nucleus reticularis rostroventrolateralis. Double-labeling experiments indicated that 71% (range: 53-80) of phenylethanolamine-N-methyltransferase-immunoreactive neurons in the nucleus reticularis rostroventrolateralis could be retrogradely labeled from the thoracic cord, as were 76% (range: 67-94) following tracer injection in the central tegmental tract at pontine levels. Triple-labeling experiments indicated that 88% (range: 82-93) of nucleus reticularis rostroventrolateralis neurons with projections to both spinal cord and central tegmental tract were phenylethanolamine-N-methyltransferase-immunoreactive. Single-unit recording, in nucleus reticularis rostroventrolateralis, was used to identify antidromic potentials elicted from stimulation sites in the spinal cord and/or central tegmental tract. Since clonidine is known to reduce central adrenaline turnover, sensitivity to this drug was used to identify putative adrenergic neurons. Twenty-six nucleus reticularis rostroventrolateralis neurons with axonal projections to both the ipsilateral spinal cord and the central tegmental tract were recorded in halothane-anesthetized rats. All these cells were barosensitive, pulse-modulated, and 16 of the 16 cells tested exhibited a 66 +/- 8% reduction in activity upon the intravenous administration of clonidine (20 micrograms/kg). Most (13 out of 16) exhibited a strong respiratory modulation. The conduction velocity of their spinal collateral was generally low (0.9 +/- 0.1 m/s) and their firing rate moderate (7.4 +/- 1.2 spikes/s). Forty-three nucleus reticularis rostroventrolateralis cells with axonal projections exclusively to the thoracic cord were studied for comparison. These cells were strongly barosensitive and pulse-synchronous, had a high discharge rate (25 +/- 3 spikes/s) and a moderate conduction velocity (3.4 +/- 0.3 m/s). Only one of the 15 cells tested was inhibited by clonidine and only two to these 15 cells exhibited a detectable respiratory modulation. Thus barosensitive nucleus reticularis rostroventrolateralis neurons with axonal projections to both the spinal cord and the central tegmental tract likely belong to the C1 adrenergic cell group. It is concluded that this subgroup of adrenergic neurons probably subserves a vasomotor function.

Adrenergic neurons in sheep brain demonstrated by immunohistochemistry with antibodies to phenylethanolamine N-methyltransferase (PNMT) and dopamine-beta-hydroxylase (DBH): absence of the C1 cell group in the sheep brain

Using immunohistochemistry with specific antisera against dopamine-beta-hydroxylase and phenylethanolamine N-methyltransferase, we present the first description of the adrenergic structures of the sheep medulla oblongata. Dopamine-beta-hydroxylase-immunoreactive perikarya in the sheep brain are localized as described in the rodents (A1 and A2 groups) but their distribution is characterized by only one phenylethanolamine N-methyltransferase immunoreactive cell body group, found in the nucleus tractus solitarius. This group corresponds to the C2 group previously described in the rat, but neither group C1 nor group C3 are found in the sheep with our method. Compared with rodents or primates, this animal presents a different pattern of central adrenergic innervation and could be an alternative model to study the central role of adrenaline in various physiological functions as different as swallowing or reproduction.

Tyrosine hydroxylase-like and dopamine beta-hydroxylase-like immunoreactivity in the gustatory zone of the nucleus of the solitary tract in the hamster: light- and electron-microscopic studies

A quantitative electron-microscopic analysis has been conducted on the neurons within the gustatory zone of the nucleus of the solitary tract of the hamster. The most common group of neurons within the gustatory zone contains both large (X1) and small (X3) members that possess deeply invaginated nuclear profiles. These neurons have somal areas that average 113 micron2 (range 34-281 micron2) and a value of somal area/nuclear area that averages 2.2. Other large and small neurons that have non-invaginated nuclear profiles are also observed. The larger (X2) neurons average 151 micron2 (range 49-487 micron2) and have much cytoplasm and associated membranous organelles that is reflected in a mean value of somal area/nuclear area of 2.6. Members of the X2 group are the largest neurons in the gustatory zone. The smaller (X4) group contains the smallest neurons in the gustatory zone of the nucleus of the solitary tract, averages 50 micron2 (range 16-103 micron2), shows almost no perinuclear cytoplasm and has a mean value of somal area/nuclear area of only 1.5. These findings are consistent with and expand upon the results of similar studies at the light-microscopic level. This grouping has been used to explore the association of tyrosine hydroxylase-like and dopamine beta-hydroxylase-like immunoreactivities with specific populations of neurons that are known to be distributed across the various levels of the gustatory zone. At the light-microscopic level, numerous well-defined and intensely labelled tyrosine hydroxylase-like immunoreactive somata of various morphologies and sizes are observed. Quantification at the electron-microscopic level indicates that 10-15% of the neurons encountered in the dorsal and intermediate levels of the gustatory zone are immunoreactive. The ventral level of the gustatory zone contains few immunoreactive neurons. Tyrosine hydroxylase-like immunoreactive neurons possess either non-invaginated or invaginated nuclear profiles and their somal areas average 106 and 142 micron2, respectively. On the bases of size and ultrastructural features, these immunoreactive somata are assigned to the two groups (X1 and X2) of large neurons within the gustatory portion of the nucleus of the solitary tract. In general, small neurons are not immunoreactive. The distribution of dopamine beta-hydroxylase-like immunoreactivity has also been examined in adjacent sections in order to reveal the presence of any putative noradrenergic neurons in the gustatory zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Biochemical evidence for presence of dopamine beta-hydroxylase in rat retina

Previously, we demonstrated immunocytochemically that certain phenylethanolamine N-methyltransferase neurons in the inner nuclear layer of rat retina contain other catecholamine synthesizing enzymes, including tyrosine hydroxylase and aromatic-L-amino acid decarboxylase but not dopamine beta-hydroxylase (DBH), the norepinephrine biosynthetic enzyme. In the present study by using a sensitive radioenzymatic assay for DBH we demonstrated the presence of DBH enzymatic activity in retinal extracts. Immunocytochemical studies, however, failed to demonstrate DBH-immunoreactive perikarya even in animals pretreated with colchicine, an inhibitor of axonal transport. Probably causes for these discrepant findings are discussed.

Catecholaminergic neurons in the ventrolateral medulla and nucleus of the solitary tract in the human

Catecholaminergic neurons in the ventrolateral medulla (VLM) and nucleus of the solitary tract (NTS) are important because of their presumed roles in autonomic regulation, including the tonic and reflex control of arterial pressure, neuroendocrine functions, and the chemosensitivity associated with the ventral medullary surface. However, little is known about the connections of these neurons in the human brain. As a first step in analyzing the functional biochemical anatomy of catecholamine neurons in the human, we used antisera against tyrosine hydroxylase (TH) and phenylethanolamine N-methyltransferase (PNMT) to localize medullary catecholamine-containing neurons and processes in the VLM and the NTS. Cells staining for TH were located throughout the VLM. Most cells staining for TH and PNMT, which are therefore adrenergic, occurred in an area of the VLM probably corresponding to the rostroventrolateral reticular nucleus. Axons of TH-immunoreactive neurons in the VLM projected (1) dorsally, in a series of parallel transtegmental trajectories, toward the dorsomedial reticular formation, the NTS, and vagal motor nucleus, (2) longitudinally, through the central tegmental field, as fascicles running parallel to the neuraxis, (3) ventrolaterally toward the ventral surface (VS) of the rostral VLM where they appeared to terminate, and (4) medially into the raphe, where they arborized. Similar systems of fibers were labeled for PNMT; the longitudinal bundles of PNMT-labeled axons were limited to the principal tegmental bundle and concentrated dorsally. Fibers containing PNMT were also identified in the medullary raphe, on the medullary ventral surface, and contacting intraparenchymal blood vessels. In the NTS, neurons exhibited immunoreactivity to both TH and PNMT: Four principal subgroups of TH-immunoreactive neurons were seen: a ventral, an intermediate, a medial, and a dorsal group. Perikarya containing PNMT were restricted to the dorsolateral aspect of the NTS. Processes containing TH and PNMT immunoreactivity were identified in the medial and dorsolateral NTS; others appeared to project between the NTS and the VLM and within the solitary tract. The presence of catecholaminergic fibers of the VLM interconnecting with the NTS, raphe, intraparenchymal microvessels, VS, and possibly the spinal cord suggests that the autonomic and chemoreceptor functions attributed to these neurons also may apply to the human.

Neuropeptide and serotonin immunoreactive neurons in the cat ventrolateral medulla

The distribution of cell bodies containing serotonin (5-HT)-, substance-P (SP)-, neurotensin (NT)-, and somatostatin (SS)-like immunoreactivity (IR) in ventrolateral medulla (VLM) of the cat was studied immunohistochemically after administration of colchicine into the cisterna magna. Perikarya containing 5-HT-, SP-, NT- or SS-IR were found throughout the rostrocaudal extent of the VLM. Although neurons containing the different neuroactive substances appeared to have an overlapping distribution in VLM, some distinct differences were observed. In the caudal VLM most of the immunoreactive cell bodies observed contained 5-HT-IR. These neurons were found primarily in the region medial to lateral reticular nucleus (LRN) around the exiting intramedullary rootlets of the hypoglossal nerve (12N). In the intermediate region of VLM, perikarya containing 5-HT- and SP-IR were observed primarily near the ventrolateral surface of the medulla in the region around the exiting rootlets of the 12N. In contrast, most of the cells containing NT- and SS-IR were consistently observed to occupy a region in the medullary reticular formation immediately dorsal to that where 5-HT- and SP-IR perikarya were found. Finally, most of the immunoreactive perikarya were found in the rostral VLM; perikarya containing 5-HT- and SP-IR were observed throughout the nucleus paragigantocellularis lateralis (PGL) near the ventrolateral surface of the medulla. These data indicate that neurons immunoreactive to either 5-HT or several different neuropeptides were located in regions of VLM which have previously been implicated in the control of arterial pressure. As regions of VLM containing these neuroactive substances in neuronal perikarya have been shown to have direct connections with spinal sympathetic areas it is likely that these VLM cells are components of neuronal circuits involved in homeostatic mechanisms controlling the circulation.

Norepinephrine throughout the spinal cord of the cat: I. Normal quantitative laminar and segmental distribution

Norepinephrine (NE) concentrations were measured by radioenzymatic assay in microdissected individual laminae of each segment of the cat spinal cord. Norepinephrine was detected in all areas of the spinal gray matter and showed more than a 7-fold difference in concentration between the laminae with the highest and lowest NE. The cervical, thoracic, and lumbosacral spinal regions showed significant interlaminar differences in NE. Intersegmental changes in NE were seen within single laminae of the thoracic and lumbosacral spinal cord, but not in the cervical spinal cord. A significant rostral to caudal, increasing regional gradient of NE was observed from the cervical to lumbosacral spinal cord in laminae I-III, V, VI, VII, and IX. In the intermediolateral cell column (IML), epinephrine concentrations were 2 to 5% of NE. Neither neurotransmitter showed a significant intersegmental variation in the IML. These data should prove useful in further defining the precise role of NE in specific regions of the spinal cord that mediate sensory, motor, autonomic, or propriospinal functions.