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D J Reis

Publications and source records attributed to D J Reis.

At least 217 records · Page 12Linked to original sources
PubMed1988

An endogenous substance with clonidine-like properties: selective binding to imidazole sites in the ventrolateral medulla.

We sought to characterize the interactions of an endogenous clonidine-displacing substance (CDS) with the specific receptor sites to which clonidine and its analogs bind: (a) the non-adrenergic imidazole binding site, which is present in the ventrolateral medulla (VLM) but not the frontal cortex, (b) high-affinity and (c) low-affinity states of the alpha 2-adrenergic receptor, and (d) the alpha 1-adrenergic receptor. CDS, like clonidine, potently and completely inhibited specific p-[3H]aminoclonidine binding to membranes from the VLM or from the frontal cortex. Both CDS and clonidine bound with highest affinity to imidazole binding sites in the VLM, both were 3-fold selective for high-affinity over low-affinity alpha 2-adrenergic receptors, and both exhibited lowest affinity for alpha 1-adrenergic receptors. Unlike clonidine, CDS exhibited 30-fold selectivity for imidazole over alpha 2-adrenergic receptors but showed only a weak preference for alpha 2- over alpha 1-adrenergic receptors, indicating that CDS and clonidine are not identical. We conclude that CDS is an endogenous clonidine-like substance which may be the natural ligand for imidazole binding sites in the VLM. The receptor-binding properties of CDS are consistent with the view that it is a unique and as yet unrecognized compound.

Animals↗
PubMed1988

A specific antiserum recognizes clonidine-displacing substance: implications for the structure of the brain's own clonidine.

A polyclonal antiserum was raised in rabbit against the clonidine analog p-aminoclonidine (PAC) coupled to hemocyanin. The antiserum (anti-PAC3) exhibited high affinity for unconjugated [3H]PAC (Kd 0.32 +/- 0.07 nM) in a rapid-filtration radioimmunoassay. Competition experiments showed that PAC, clonidine, and naphazoline cross-reacted with the anti-PAC3 antiserum, whereas a number of other structurally related compounds did not. An endogenous clonidine-displacing substance (CDS) partially purified from bovine brain also inhibited specific [3H]PAC binding to anti-PAC3 in a dose-dependent manner. Thus, (a) anti-PAC3 antiserum is specific for clonidine and closely related compounds, and (b) CDS may structurally resemble clonidine since it is recognized by this highly specific antiserum.

Animals↗
PubMed1988

Spontaneous release of endogenous aspartate and glutamate from rat striatal slices is increased following destruction of local neurons by ibotenic acid.

We sought to determine in rat striatum whether the release of neurotransmitter amino acids aspartate (Asp), glutamate (Glu) and gamma-aminobutyric acid (GABA) were affected by local neurons. To do so, unilateral microinjections of ibotenic acid, and excitotoxin that destroys local neurons without affecting fibers of passage, were made into the striatum. Release of endogenous amino acids from lesioned and intact striatal slices were measured by HPLC one week later. The effectiveness and specificity of the lesion were confirmed by measuring the enzyme activity associated with extrinsic dopamine neurons (tyrosine hydroxylase; 111 +/- 14%), intrinsic GABA neurons (glutamic acid decarboxylase; 19 +/- 7%) and intrinsic acetylcholine neurons (choline acetyltranferase; 37 +/- 10%). Destruction of local striatal neurons markedly attenuated the release of GABA (41 +/- 12% of control) elicited by depolarization with K+ (35 mM), but did not significantly reduced the K+-evoked release of Asp (80 +/- 17%) and Glu (92 +/- 8%). However, spontaneous release of Asp and Glu was significantly greater than that observed in unlesioned tissue (159 +/- 18% and 209 +/- 27%, respectively), while the spontaneous release of GABA was not significantly reduced (75 +/- 43%). Although release of the neurotransmitter amino acids Asp, Glu and GABA were affected by the lesion, the release of the non-neurotransmitter amino acid tyrosine was unaffected. These data are consistent with the hypotheses that: 1) the predominant source of releasable stores of endogenous Asp and Glu in the striatum arises from extinsic neurons, and 2) that the spontaneous release of Asp and Glu from axon terminals in the striatum may be regulated, at least in part, by local inhibitory neurons.

Amino Acids↗
PubMed1988

Hypotensive action of clonidine analogues correlates with binding affinity at imidazole and not alpha-2-adrenergic receptors in the rostral ventrolateral medulla.

Clonidine acts within the rostral ventrolateral medulla to lower arterial pressure. The receptor mechanism for this action is unknown. In the rostral ventrolateral medulla clonidine binds not only to the alpha 2-adrenergic receptor but also to a novel class of sites which are specific for imidazolines and imidazoles and are distinct from adrenergic or histaminergic receptors. In order to distinguish whether a putative imidazole receptor or the alpha 2-receptor mediates the clonidine hypotensive response, a series of clonidine analogues were tested (1) in radioligand binding assays of their affinity at imidazole and alpha 2-adrenergic receptors, and (2) by microinjection into the rostral ventrolateral medulla of anaesthetized rats to measure their capacity to lower arterial pressure. The hypotensive response elicited by the test agents was strongly correlated with affinity at imidazole sites (r = 0.92) but not with alpha 2-adrenergic affinity (r = 0.36). An imidazole receptor in the rostral ventrolateral medulla may participate in the hypotensive action of clonidine.

Animals↗
PubMed1988

Cells proliferating in vitro to local brain injury are primarily of hematic origin and differ from those associated with anterograde degeneration.

(a) The PR elicited by excitotoxic destruction of intrinsic neurons in the CN has a rapid onset, peaks within 2 weeks, and persists indefinitely; (b) the majority of the proliferating cells are not intrinsic to the CNS but are of hematic origin; (c) a small mirror-image response is seen in the contralateral CN; (d) the proliferating response in anterogradely degenerating terminals in SN differs in time course, magnitude, and phenotypically from that initiated by direct neuronal loss. We conclude that the majority of proliferating cells at the site of selective neuronal injury in brain are of hematic origin in contrast to that initiated during anterograde degeneration, which consists primarily of intrinsic cells of brain (glia).

Animals↗
PubMed1988

The C1 area of the brainstem in tonic and reflex control of blood pressure. State of the art lecture.

Recent studies have demonstrated that the neurons of the lower brainstem that are responsible for maintaining normal levels of arterial pressure reside in a specific area of the rostral ventrolateral medulla. In rat, the critical zone corresponds to a small region containing a subpopulation of the adrenergic C1 group, defined immunocytochemically by the presence of the epinephrine-synthesizing enzyme phenylethanolamine N-methyltransferase. Neurons of this region (the C1 area), possibly including the adrenergic neurons, directly innervate preganglionic neurons in the spinal cord, and are tonically active and sympathoexcitatory. The excitatory transmitter released into the spinal cord is unknown. The discharge of C1 area neurons is locked to the cardiac cycle and, in turn, leads to firing of sympathetic preganglionic neurons. The C1 area neurons are inhibited by baroceptor input and mediate the vascular component of baroceptor reflexes. They also mediate somato-sympathetic pressor responses from skin and muscle and participate in reflex responses to hypoxia. The neurons are directly innervated by local neurons containing gamma-aminobutyric acid, acetylcholine, enkephalin, and substance P, all of which modulate arterial pressure. The C1 area is the site of the hypotensive actions of clonidine. Clonidine appears to act on imidazole receptors in the C1 area to lower arterial pressure. The natural ligand for these receptors may be a newly defined substance in brain, clonidine-displacing substance. Neurons of the C1 area appear to be the critical neuronal group governing the normal resting and reflex control of arterial pressure. They may play a critical role in the maintenance of elevated arterial pressure in hypertension and as a site of action of antihypertensive drugs.

Animals↗
PubMed1988

Clonidine-specific antibodies as models for imidazole and alpha 2-adrenergic receptor binding sites: implications for the structure of clonidine-displacing substance.

Polyclonal antisera raised against para-aminoclonidine coupled to haemocyanin exhibit high affinity for para-aminoclonidine, clonidine and chloroethylclonidine (IC50 less than 100 nmol/l). Anti-para-aminoclonidine antibodies also cross-react with naphazoline, oxymetazoline and tolazoline at moderate concentrations (IC50, 300-500 mumol/l); the phenyl-imidazoles detomidine, medetomidine and MPV830 are weakly cross-reactive (IC50 greater than 0.2 mmol/l). All of these compounds bind with high affinity to both imidazole and alpha 2-adrenergic receptors. Compounds which are imidazole- or alpha 2-specific do not cross-react with anti-para-aminoclonidine antibodies (IC50 greater than 1 mmol/l). Anti-para-aminoclonidine also recognizes an endogenous clonidine-displacing substance in the brain. Thus, (a) binding to anti-para-aminoclonidine antibodies defines a subset of phenyl-imidazol(in)e ligands which bind to both imidazole and alpha 2-adrenergic receptors, suggesting that anti-para-aminoclonidine recognition sites resemble a hybrid of the two receptor types; (b) antibodies to imidazole- or alpha 2-specific agents may be useful as models for differentiating between these types; (c) since clonidine-displacing substance is recognized by anti-para-aminoclonidine antibodies, it may have phenyl and imidazole rings as parts of its chemical structure.

Animals↗
PubMed1988

Different projections of the central amygdaloid nucleus mediate autonomic and behavioral correlates of conditioned fear.

The purpose of the present study was to determine whether lesions of areas projected to by the central amygdaloid nucleus (ACE) would disrupt the classical conditioning of autonomic and/or behavioral emotional responses. The areas studied included 3 projection targets of the ACE: the lateral hypothalamic area (LH), midbrain central gray (CG) region, and bed nucleus of the stria terminalis (BNST). Lesions were made either electrolytically or by microinjection of ibotenic acid, which destroys local neurons without interrupting fibers of passage. Two weeks later, the animals were classically conditioned by pairing an acoustic stimulus with footshock. The next day, conditioned changes in autonomic activity (increases in arterial pressure) and emotional behavior ("freezing," or the arrest of somatomotor activity) evoked by the acoustic conditioned stimulus (CS) were measured during extinction trials. Electrolytic and ibotenic acid lesions of the LH interfered with the conditioned arterial pressure response, but did not affect conditioned freezing. Electrolytic lesions of the rostral CG disrupted conditioned freezing but not conditioned changes in arterial pressure. Ibotenic acid injected into the rostral CG reduced neither the arterial pressure nor the freezing response. Injection of ibotenic acid in the caudal CG, like electrolytic lesions of the rostral CG, disrupted the freezing, but not the arterial pressure response. Injection of ibotenic acid into the BNST had no effect on either response. These data demonstrate that neurons in the LH are involved in the autonomic, but not the behavioral, conditioned response pathway, whereas neurons in the caudal CG are involved in the behavioral, but not the autonomic, pathway. Different efferent projections of the central amygdala thus appear to mediate the behavioral and autonomic concomitants of conditioned fear.

Amygdala↗
PubMed1988

Stimulation of opiate receptors in the dorsal pontine tegmentum inhibits reflex contraction of the urinary bladder.

In urethane-anesthetized rats the i.v. administration of the potent short-acting opioid, fentanyl, elicited inhibition of rhythmic spontaneous reflex increases in vesical pressure (VP) evoked by urinary bladder distension. The duration of fentanyl-induced inhibition was dose-related between 0.8 and 8.0 micrograms/kg i.v. Pretreatment with the opiate receptor antagonist, naloxone HCl (250 micrograms/kg i.v.), antagonized completely fentanyl's effect on VP rhythm. Results similar to those obtained with fentanyl were observed after the bilateral stimulation of opiate receptors in the dorsolateral tegmental-subceruleus region of the pons (DLT-SC region) with D-Ala2-Met5-enkephalinamide (DAMA) microinjections. These inhibitory effects were dose-related and significant between 1.0 and 100.0 ng/site. DAMA in the DLT-SC did not alter basal cardiorespiratory parameters. The systemic and local administration of naloxone reversed rapidly the VP effects elicited by DAMA in the DLT-SC region. Naloxone alone, administered either i.v. or locally in the DLT-SC region, increased the frequency of spontaneous reflex increases in VP. Moreover, pretreatment of the DLT-SC region with naloxone microinjections significantly (55% reduction) decreased the duration of fentanyl (8.0 micrograms/kg i.v.)-induced inhibition of VP rhythm. Neurons in DLT-SC region whose discharge increased just before and throughout spontaneous increases in VP (vesical contraction-related units), were inhibited rapidly and completely by the systemic administration of fentanyl. However, fentanyl elicited a prolonged decremental discharge in neurons of the DLT-SC region with discharge patterns related to vesical relaxation (vesical relaxation-related units).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1988

Reticulospinal vasomotor neurons of the rat rostral ventrolateral medulla: relationship to sympathetic nerve activity and the C1 adrenergic cell group.

Neurons projecting from the rostral ventrolateral medulla (RVL) to the spinal cord were antidromically identified in rats anesthetized with urethane, paralyzed, and ventilated. The sites of lowest antidromic threshold were concentrated in the intermediolateral nucleus (IML). Their axonal conduction velocities were distributed bimodally, with the mean of the rapidly conducting fibers (greater than 1 m/sec) being 3.1 +/- 0.1 m/sec (n = 105), and of the slower axons being 0.8 +/- 0.03 m/sec (n = 25). Single-shock electrical stimulation of RVL elicited 2 bursts of excitation in splanchnic sympathetic nerve activity (SNA), which resulted from activation of 2 descending pathways with conduction velocities comparable to those of antidromically excited RVL-spinal neurons. The probability of discharge of RVL-spinal cells was synchronized both with the cardiac-related bursts in SNA with functional baroreceptor reflexes and with the free-running 2-6 Hz bursts in SNA following baroreceptor afferent denervation. On the average, their spontaneous discharges occurred 67 +/- 2 msec (n = 31) prior to the peak of the spontaneous bursts in splanchnic SNA. This time corresponded to the latency to the peak of the early excitatory potential in splanchnic SNA following electrical stimulation of RVL. Baroreceptor reflex activation inhibited RVL-spinal neurons. The recording sites of RVL-spinal vasomotor neurons were consistently located within 100 micron of cell bodies (C1 neurons) immunoreactive for the adrenaline-synthesizing enzyme phenylethanolamine N-methyltransferase (PNMT). Ultrastructural analysis of the lateral funiculus of the cervical and thoracic spinal cord demonstrated PNMT immunoreactivity within myelinated (0.6-2.1 micron diameter) and unmyelinated (0.1-0.8 micron diameter) axons. Estimated conduction velocities of these fibers were comparable to the antidromic conduction velocities of the rapidly and slowly conducting populations of RVL-spinal vasomotor neurons. We conclude that in rat, the discharge of RVL-spinal vasomotor neurons strongly influences SNA: the baroreceptor-mediated inhibition of these neurons is reflected in the cardiac locking of SNA, while, in the absence of baroreceptor input, the synchronous discharge of RVL-spinal neurons maintains a free-running 2-6 Hz bursting pattern in SNA. RVL-spinal neurons are located within, and may be elements of, the C1 adrenergic cell group, and they provide a sympathoexcitatory drive to neurons in the IML over rapidly and slowly conducting pathways that correspond to myelinated and unmyelinated spinal axons containing PNMT.

Action Potentials↗
PubMed1988

C1 area of the rostral ventrolateral medulla as a site for the central hypotensive action of propranolol.

Previous studies suggest that the hypotensive response to centrally administered propranolol results from a drug-induced release of norepinephrine which then stimulates central alpha adrenergic receptors and, as a consequence, arterial pressure is lowered. Inasmuch as the C1 area of the rostral ventrolateral medulla is known to contain noradrenergic nerve terminals and participate in arterial pressure regulation, we determined whether this medullary region is a site mediating the hypotensive response to centrally administered propranolol. Bilateral microinjections (0.1 microliter) of dl-propranolol (0.25-2 nmol) into the C1 area of urethane-anesthetized rats resulted in a gradual reduction in mean arterial pressure which was sustained throughout the 120-min experimental period. The injection site was verified pharmacologically at the end of each experiment by bilateral microinjection of 10 nmol of tyramine and observing a further decrease in mean arterial pressure and a reduction in heart rate. Pretreatment of the C1 area bilaterally with reserpine 24 hr earlier significantly reduced the hypotensive responses to microinjections of both propranolol and tyramine whereas the hypotensive response to the direct acting agonist clonidine was unchanged. These results demonstrate that the C1 area of the rostral ventrolateral medulla is a site for a central hypotensive action of propranolol. Moreover, the data provide further evidence that the hypotensive action of centrally administered propranolol results from a drug-induced release of norepinephrine from central noradrenergic neurons.

Animals↗
PubMed1987

Clonidine displacing substance is biologically active on smooth muscle.

A substance has been isolated from brain which potently inhibits the binding of clonidine to brain membranes (clonidine displacing substance, CDS). We sought to determine if CDS is biologically active on smooth muscle. CDS had no effect on vascular smooth muscle. In contrast, CDS potently contracted rat gastric fundus strips in a dose dependent manner. The contractile effect of CDS was not blocked by antagonists selective for biologically active substances known to contract the fundus strip. These results demonstrate that CDS has a unique and potent ability to selectively contract smooth muscle.

Animals↗
PubMed1987

Topographic organization of convergent projections to the thalamus from the inferior colliculus and spinal cord in the rat.

The purpose of this study was to identify thalamic areas receiving convergent sensory inputs from acoustic and spinal projection systems in the rat. The topographic distribution of afferents to the thalamus from the inferior colliculus and spinal cord was examined by using WGA-HRP as an anterograde axonal tracer. Following injections in the inferior colliculus, terminal labeling was present in ventral, medial, and dorsal divisions of the medial genicuate body (MGB) and in adjacent areas of the posterior thalamus, including the posterior limitans nucleus, the posterior intralaminar nucleus, the marginal zone, the peripeduncular region, the lateral or parvicellular part of the subparafascicular nucleus, and a region intercalated between the posterior limitans nucleus and the suprageniculate nucleus. In the caudal thalamus spinal projections remained in the reticular formation medial to the collicular terminal field. At intermediate levels of the MG, however, the spinal projection began to overlap the collicular field, terminating in the medial division of the MG and in the posterior intralaminar nucleus, the marginal zone, the lateral subparafascicular nucleus, and the area between the suprageniculate and posterior limitans nuclei. More rostrally, the convergent field expanded to include aspects of the dorsal MG division. The extent to which afferent projections to the thalamus from the inferior colliculus and spinal cord converge is thus graded in the caudorostral plane, with the greatest overlap occurring at the level of the rostral third of the MGB. These observations identify potential areas of acoustic and somesthetic integration and may account for observations of neuronal plasticity in the thalamus in response to the pairing of acoustic and somesthetic inputs.

Afferent Pathways↗
PubMed1987

Organization of central adrenergic pathways: I. Relationships of ventrolateral medullary projections to the hypothalamus and spinal cord.

We studied the organization of projections from the C1 adrenergic and A1 noradrenergic cell groups in the ventrolateral medulla (VLM) to the hypothalamus and the spinal cord by using a combination of retrograde transport of fluorescent tracers and immunocytochemistry. Three issues were addressed. Neurons in the VLM that stain immunohistochemically for phenylethanolamine N-methyltransferase (PNMT) have been assumed to be adrenergic. However, the presence of PNMT-immunoreactive neurons in the hypothalamus that do not stain for tyrosine hydroxylase (TH) prompted us to re-evaluate the VLM by an elution-restaining immunohistochemical procedure. We confirmed that nearly all of the rostral medullary PNMT-immunoreactive neurons also stained for TH. By contrast, in the caudal medulla, very few TH-positive neurons stained for PNMT. Neurons of the C1 group in the rostral VLM project both to the thoracic spinal cord and to the hypothalamus. To determine whether individual C1 neurons send collaterals to the hypothalamus and spinal cord, we injected different-colored fluorescent dyes (diamidino yellow or fast blue) into the thoracic spinal gray matter and either the median preoptic (MnPO) or paraventricular (PVH) nuclei of the hypothalamus. Very few double-labeled neurons were found in the VLM, indicating that hypothalamic and spinal cord projections arise from almost completely independent populations of cells. Approximately half of the neurons projecting to the spinal cord from rostral VLM were not immunoreactive for TH or PNMT, indicating that a substantial part of this projection is noncatecholaminergic. The MnPO and the PVH both receive extensive catecholaminergic inputs from the VLM. We also used fluorescent retrograde tracers to determine whether individual VLM neurons send collaterals to both hypothalamic sites. Approximately 20% of neurons projecting to the MnPO in the rostral two thirds of the VLM also sent collaterials to the PVH, nearly all of these neurons being TH-positive. The collateralization of the VLM catecholaminergic projection to the hypothalamus may provide an anatomical substrate for integration of fore-brain participation in cardiovascular regulation. In contrast, the adrenergic projection from the VLM to the intermediolateral column of the spinal cord arises from a separate population of neurons.

Adrenergic Fibers↗
PubMed1987

Local cholinergic mechanisms participate in the increase in cortical cerebral blood flow elicited by electrical stimulation of the fastigial nucleus in rat.

We sought to determine whether the increase in regional cerebral blood flow (rCBF) elicited within the cerebral cortex (CX) by electrical stimulation of the fastigial nucleus (FN) of the cerebellum is: prevented by local application of the muscarinic cholinergic receptor antagonist, atropine and temporally correlated with a stimulus-locked release of acetylcholine (ACh) from the cortical surface. Rats were anesthetized, paralyzed, ventilated, with arterial blood gases controlled and arterial pressure maintained within the autoregulated range. Bilateral craniotomies were performed over a standardized region of the sensory motor CX and superfusion devices stereotaxically positioned on the cortical surface. Cortical surface temperature, as well as pH, pCO2 and pO2 of the solutions applied to the cortex were also carefully controlled. rCBF was measured in dissected regions of frontal (FCX), parietal (PCX), and occipital cortices (OCX), caudate nucleus (CN), and hippocampus (HIPP) by the Kety principle using [14C]iodoantipyrine as indicator. Resting rCBF (ml/100 g/min) in unoperated control animals ranged from 70 +/- 5 in HIPP to 95 +/- 7 in PCX and was unaffected by bilateral craniotomies and placement of superfusion devices containing Kreb's bicarbonate buffer (vehicle) on the cortical surface. Local application of atropine (ATR, 100 microM) to the right PCX via the superfusion device did not affect resting rCBF. With FN stimulation rCBF increased bilaterally and symmetrically in all areas up to 227% in PCX. ATR application attenuated by 59% the FN-elicited increase in rCBF on the ipsilateral frontoparietal CX, without affecting blood flow in adjacent structures. ATR did not affect cortical cerebrovasodilation produced by hypercarbia (arterial pCO2 = 59.0 +/- 1.4 mm Hg). FN-stimulation resulted in a small (22%) but significant (P less than 0.05, n = 9) reduction in the release of [3H]ACh from the cortical surface, while supramaximal depolarization with 55 mM K+ increased [3H]ACh release by 251%. These studies indicate that: increases in cortical rCBF elicited by FN stimulation, but not hypercarbia, are in large part mediated by local muscarinic cholinergic receptors; resting rCBF is not tonically affected by muscarinic receptor activation; and the release of ACh from the cortical surface is, in general, reduced during FN-stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1987

Phenylethanolamine N-methyltransferase-containing neurons in the rostral ventrolateral medulla of the rat. I. Normal ultrastructure.

The electron microscopic localization of the adrenaline-synthesizing enzyme, phenylethanolamine N-methyltransferase (PNMT) was examined in the rostral ventrolateral medulla (RVL) of adult rats. The brains were fixed by perfusion with 3.75% acrolein and 2.0% paraformaldehyde in phosphate buffer. Coronal Vibratome sections through the RVL were immunocytochemically labeled using a rabbit polyclonal antiserum to PNMT and the peroxidase-antiperoxidase method. A semi-quantitative ultrastructure analysis revealed that the perikarya constituted 9% of the total immunoreactive profiles observed in the RVL. The labeled somata were large (18-24 microns) and were characterized by an indented nucleus and abundant cytoplasm with numerous mitochondria. An average of 136.8 +/- 11.6 mitochondria were present per 100 microns2 cytoplasm, which is 38% greater than the numbers found for PNMT-immunoreactive neurons in the nucleus of the solitary tract. Moreover, the labeled somata were often found in direct apposition to the basal lamina of small capillaries and neighboring astrocytic processes. The remaining labeled profiles were neuronal processes of which 72% were dendrites. Both the PNMT-labeled somata and dendrites received primarily symmetric contacts from unlabeled axon terminals. Only a few axons and terminals containing immunoreactivity for PNMT were observed. The axons were both unmyelinated and myelinated. The PNMT-immunoreactive terminals were characterized by a mixed population of vesicles and by the formation of synaptic junctions with both unlabeled dendrites and PNMT-labeled perikarya and dendrites. The ultrastructural morphology and proximity to blood vessels and glia suggest a high metabolic activity and possibly a chemosensory function of PNMT neurons in the RVL. The existence of myelinated and unmyelinated axons could imply that PNMT-containing neurons have different conduction velocities in efferent pathways to the spinal cord or other brain regions. Furthermore, the multiple types of synaptic interactions between labeled and unlabeled axons and dendrites support the concept that adrenergic neurons modulate and are modulated by neurons containing the same or other putative transmitters in the RVL.

Adrenergic Fibers↗
PubMed1987

Phenylethanolamine N-methyltransferase-containing neurons in the rostral ventrolateral medulla. II. Synaptic relationships with GABAergic terminals.

The ultrastructural morphology of terminals synthesizing gamma-aminobutyric acid (GABA), as indicated by peroxidase immunoreactivity for its synthetic enzyme L-glutamate decarboxylase (GAD), was examined in the rostral ventrolateral medulla (RVL) of the adult rat brain. The objective of the study was to determine the types of synaptic associations between the GABAergic terminals and other neurons in the RVL, particularly the C1-adrenergic neurons containing phenylethanolamine N-methyltransferase (PNMT). The brains were fixed by perfusion with 3.75% acrolein and 2.0% paraformaldehyde in phosphate buffer. Coronal Vibratome sections through the RVL were singly labeled with a sheep antiserum to GAD using the peroxidase-antiperoxidase (PAP) method. Additional sections were dually labeled using the PAP technique for the GAD antiserum and immunogold labeling for a rabbit antiserum against PNMT. Ultrastructural analysis revealed that peroxidase labeling for GAD was localized primarily to axons and axon terminals in both single and dual labeled material. The axons were small and unmyelinated. The GAD-labeled terminals were 0.5-2.0 microns in diameter and contained a large population of small clear vesicles usually associated with a few mitochondria. These terminals formed synapses with many dendrites, a few nerve cell bodies and axon terminals. The junctions were all symmetric and the postsynaptic structures failed to exhibit immunoreactivity when processed only for GAD labeling. In sections incubated with both GAD and PNMT antisera, the peroxidase-labeled GABAergic terminals formed symmetric synapses with nerve cell bodies and dendrites showing immunogold labeling for PNMT. In addition, the GAD-labeled terminals were presynaptic to other dendrites which appeared to have equal access to the antisera and gold markers, but failed to exhibit detectable immunoreactivity for PNMT. Both the PNMT-labeled and unlabeled somata and dendrites also received symmetric and asymmetric contacts from terminals containing neither GAD nor PNMT-immunoreactivity. We conclude that GABA is at least one of the inhibitory transmitters regulating adrenergic as well as non-adrenergic outflow from the RVL.

Adrenergic Fibers↗