Rat Medulla Oblongata Research Articles

Site-specific effects of apelin-13 in the rat medulla oblongata on arterial pressure and respiration

Apelin peptides are now known to be endogenous ligands at the orphan G-protein coupled receptor, APJ. Apelin and its receptor have been found in the brainstem and shown to have a role in haemodynamic homeostasis when injected intravenously. The physiological role of this peptide and its receptor centrally are yet to be elucidated. In this study, urethane anaesthetised, paralysed and ventilated male Sprague–Dawley rats (350–450 g, n=4) were used to investigate the action of apelin-13 microinjected directly into the nucleus tractus solitarius (NTS) and the rostral ventrolateral medulla (RVLM) on arterial pressure and phrenic nerve activity. Apelin-13 microinjections (4 mmol/l, 50 nl) into the NTS resulted in either apnea or decreased phrenic nerve discharge amplitude by up to 30%. In the RVLM, apelin-13 caused either a 100–200% increase, or a 10–30% increase in phrenic nerve discharge amplitude depending on the exact site of injection. Increases of 10–20 mm Hg in arterial pressure were also evoked from both the NTS and the RVLM. These data suggest a role for apelin-13 in arterial pressure and respiratory control in the NTS and the RVLM.

Atypical on-, off- and neutral cells in the rostral ventromedial medulla oblongata in rat.

It is generally assumed that the response pattern of on-, off- and neutral cells in the rostral ventromedial medulla (RVM) to noxious stimulation is independent of stimulation site. But recent studies have shown that a remarkable number of RVM neurons do not have whole-body receptive fields. These so-called atypical neurons were extracellularly recorded in lightly anaesthetized rats. The receptive fields to noxious thermal and mechanical stimulation applied to the tail, the extremities and the craniofacial region were determined in 57 RVM neurons. In 24 atypical off-cells, 12 on-cells and 21 neutral cells, the response pattern evoked by noxious pinch to the nose, forehead and ear most frequently differed from the responses to noxious tail heat. The modulatory effects of intravenously administered morphine were examined in 21 cells. In contrast to the general assumption that morphine activates off-cells, inhibits on-cells and has no effect on neutral cells, in atypical RVM neurons 5 of 6 off-cells, 2 of 6 on-cells and 5 out 9 neutral cells showed a different response pattern to systemical administration of morphine. The results show that a RVM cell classification that is exclusively based on the behaviour to noxious tail heat can neither sufficiently predict the response pattern to different noxious stimuli, especially in the craniofacial region, nor reliably predict the modulatory effect of morphine in RVM neurons. The fact that the neutral cells responded in an off or on manner to noxious stimulation different from noxious tail heat and that morphine modulated activity in many neutral cells suggests that these cells are probably subtypes of on- and off-cells.

It’s Renin in the Brain

Since the first description of renin, angiotensinogen and angiotensin as well as converting enzyme and angiotensin receptors in the brain exactly 30 years ago,1–5⇓⇓⇓⇓ there was a heated debate, whether an endogenous intrinsic brain renin- angiotensin system (RAS) exists or not.6,7⇓ For a long time, the “believers” of local angiotensin II generation by the brain RAS were in a minority. Even at a symposium 1981, celebrating the 10-year anniversary of the discovery of the brain RAS, there was skepticism and the question whether the “renin-like” enzyme in brain was identical with cathepsins, tonin, or other proteases was a matter of debate. Historically, it is interesting that the presence in the brain of other classically peripheral peptides such as insulin, glucagon, and substance P was accepted without identification of the local synthetic pathway and less controversial than angiotensin as neuropeptide. Open letters, public debates, and personal accusations nourished sometimes emotional controversy whether angiotensin could be generated locally in tissue. The brain was a model for angiotensin generating pathways in other extrarenal tissues because the blood-brain barrier, which is impermeable for proteins and peptides, made it more unlikely that the RAS components measured in the brain were contaminations from the plasma. Angiotensin has extremely powerful effects on the brain that synergistically increase blood volume and blood pressure, eg, by stimulation of water intake and salt appetite, release of various pituitary hormones, increase of sympathetic tone, and decrease of baroreceptor reflex.7 The local generation of angiotensin II in the brain by an endogenous intrinsic RAS could therefore be extremely important for cardiovascular control and beyond. With the advent of transgenic technology, novel approaches to study the mechanistic and functional aspects of the brain RAS became available. Renin and angiotensinogen could be overexpressed or ablated …

Naloxone-Precipitated Morphine Withdrawal Elicits Increases in c-fos mRNA Expression in Restricted Regions of the Infant Rat Brain

This paper is the first report of a genetic index for morphine withdrawal in infant rats. We examined the effects of naloxone (2 mg/kg) on c-fos mRNA levels in brains of infant and adult rats following repeated treatment with morphine (20 mg/kg, once daily for 5 days). One hour after a single administration of naloxone (naloxone challenge), an increase in c-fos mRNA was observed in the olfactory bulb, hypothalamus and medulla oblongata of infant rats, and in the olfactory bulb and hypothalamus, but not in the medulla oblongata of adult rats. The c-fos mRNA levels returned to control levels 6 h after the naloxone challenge. The increase in c-fos mRNA levels was followed by body weight loss in both infant and adult rats. When MK-801, a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, was co-administered along with morphine, it inhibited the naloxone-induced increases in c-fos mRNA levels in infant rats following repeated morphine administration. These results suggest that physical dependence develops in infant rats following repeated morphine administration and that the increment of c-fos mRNA levels is a useful indicator for naloxone-precipitated morphine withdrawal in infant as well as in adult rats.

Differential Expression of Prolactin Releasing Peptide and Tyrosine Hydroxylase in Fibers Derived from the Same Neurons in the Rat.

We found differential expression of two neuronal markers in nerve fibers that came from the same neuronal somata. Prolactin releasing peptide (PrRP) and tyrosine hydroxylase (TH), a catecholamine synthesis rate-limiting enzyme, were differentially distributed in distinct fibers derived from the same neuronal cell body located in the rat medulla oblongata. All PrRP-immunoreactive neurons were catecholaminergic at the cell body level in the nucleus tractus solitarius (NTS) and in the ventral and lateral reticular nuclei (VLRN). However, in the terminal areas such as the bed nucleus of the stria terminalis (BNST) and paraventricular nucleus (PVN), where fibers are projected from both PrRP and TH positive neurons in the NTS and VLRN, dense PrRP immunoreactive fibers were observed that did not contain TH. In the medulla oblongata, proximal fibers near a neuronal cell body that contained both TH and PrRP were diverged into mainly PrRP-positive or mainly TH-positive fibers. These results suggest that TH and PrRP are differentially expressed between fibers from the same cell body. The fibers containing predominantly PrRP have been detected at birth, so the machinery to transport PrRP and TH separately may be established at an embryonic stage.

Neurotransmitter Levels in Brains of Chronically Jiawey Siwu-Treated Rats

Levels of monoamines and metabolites, excitatory amino acids, and gamma-aminobutyric acid (GABA) were investigated in discrete brain areas of chronic Jiawey Siwu (JS)-treated rats. Male Sprague-Dawley rats were dosed orally for 3 months with normal saline or JS at 0.21, 1.05 or 4.2 g/kg/day. Body weights of these four groups were similar over 3 months. Most effects of JS revealed a dose dependency with levels of neurotransmitters. Levels of norepinephrine (NE) and epinephrine (EPI) in cerebral cortex; EPI, vanillylmandelic acid (VMA), dopamine (DA) and 5-hydroxytryptamine (5-HT) in medulla oblongata; DA in midbrain; NE and 5-HT in amygdala; and 5-HT in hypothalamus had decreased in JS-treated rats. 3-Methoxytyramine (3-MT) in cerebral cortex; 5-hydroxyindole-3-acetic acid (5-HIAA) in medulla oblongata; NE, 3-MT and homovanillic acid (HVA) in pons; EPI and 3-MT in midbrain; 3-MT and HVA in amygdala; 3-MT, 3,4-dihydroxyphenylacetic acid (DOPAC), HVA and 5-HIAA in cerebellum; HVA in hypothalamus; and DOPAC and HVA in hippocampus had all increased in JS-treated rats. In pons, 5-HT increased with low and decreased with high JS doses. Ratios of DA/3-MT in pons and midbrain; DA/HVA in pons and cerebellum; and 5-HT/5-HIAA in medulla oblongata, cerebellum and hypothalamus had decreased. Furthermore, aspartate (ASP) and glutamate (GLU) levels had decreased in cerebral cortex, midbrain, hypothalamus and hippocampus or amygdala, and increased in pons. GABA levels were reduced in cerebral cortex, and higher in medulla oblongata, pons, amygdala, cerebellum, hippocampus and striatum of JS-treated rats. These results indicate that the synthesis and (or) metabolism of NE, DA, EPI and 5-HT, and the levels of ASP, GLU and GABA in rat brains were differentially regionally altered by JS, which may contribute to the central manifestations of JS treatment.

Ventrolateral neurons of medullary organotypic cultures: intracellular pH regulation and bioelectric activity

The hypothesized role of the intracellular pH (pH i) as a proximate stimulus for central chemosensitive neurons is reviewed on the basis of data obtained from organotypic cultures of the medulla oblongata (obex level) of new born rats (OMC). Within OMC a subset of neurons responds to hypercapnia as do neurons in the same (or similar) brain areas in vivo. Maneuvers altering intra- and/or extracellular pH (pH o) such as hypercapnia, bicarbonate-withdrawal, or ammonium pre-pulses, evoked well defined changes of the neuronal pH i. During hypercapnia (pH o 7.0) or bicarbonate-withdrawal (pH o 7.4) most ventrolateral neurons adopted a pH i which was ≤0.2 pH units below the steady state pH i, while signs of pH i-regulation occurred only in a small fraction of neurons. During all treatments leading to intracellular acidosis, bioelectric activity of chemosensitive neurons increased and was often indistinguishable from the response to hypercapnia, regardless of whether pH o was unchanged, decreased or increased during the treatment. These data strongly suggest that the pH i acts as proximate stimulus. The mode of acid extrusion of chemosensitive neurons is, therefore, of major importance for the control of central chemosensitivity. Immunocytochemical data, pH i measurements and neuropharmacological studies with novel drugs pointed to the Na +/H + exchanger subtype 3 (NHE3) as a main acid extruder in ventrolateral chemosensitive neurons. Possible functions and neuropharmacological strategies arising from this very local NHE3 expression are discussed.

The projections of the midbrain periaqueductal grey to the pons and medulla oblongata in rats.

It is now established that stimulation of the ventrolateral midbrain periaqueductal grey (PAG) evokes inhibition of nociceptive spinal neurons, which results in analgesia and a powerful attenuation of pain behaviour. It is postulated that the PAG exerts this inhibitory effect on spinal nociceptive functions through the activation of descending serotonergic and noradrenergic pathways that arise from the rostral ventromedial medulla (RVM) and pontine noradrenergic nuclei. To investigate the neuroanatomical substrate of this functional link between the PAG and RVM, as well as the pontine noradrenergic nuclei in the rat, we labelled axons that project from the ventrolateral PAG to various regions of the pons and medulla oblongata using the anterograde tracing substance, Phaseolus vulgaris leucoagglutinin. We demonstrated that some of PAG efferents really do terminate in the RVM and pontine noradrenergic nuclei, but a substantial proportion of them project to the intermediate subdivision of the pontobulbar reticular formation. Combining the axonal tracing with serotonin- and tyrosine-hydroxylase-immunohistochemistry, we also found that, in contrast to previous results, PAG efferents make relatively few appositions with serotonin- and tyrosine-hydroxylase-immunoreactive neurons in the RVM and pontine noradrenergic nuclei; most of them terminate in nonimmunoreactive territories. The results suggest that the ventrolateral PAG may activate a complex pontobulbar neuronal assembly including neurons in the intermediate subdivision of the pontobulbar reticular formation, serotonin- and tyrosine-hydroxylase-immunoreactive and nonimmunoreactive neurons in the RVM and pontine noradrenergic nuclei. This pontobulbar neural circuitry, then, may mediate the PAG-evoked activities towards the spinal dorsal horn resulting in the inhibition of spinal nociceptive functions.

γ-Aminobutyric Acid Receptor (GABAA) Subunits in Rat Nucleus Tractus Solitarii (NTS) Revealed by Polymerase Chain Reaction (PCR) and Immunohistochemistry

Expression of mRNAs encoding seven GABAA receptor subunits (α1, α2, α3, α5, β2, β3, γ2) in the nucleus tractus solitarii (NTS) of rat medulla oblongata was examined by reverse transcription-polymerase chain reaction (RT-PCR). All subunit mRNAs, except α5, were clearly detected. Band densities produced by α1, α3, β3, and γ2 subunits were greater than those corresponding to β2 and α2 transcripts. The localization of these subunits in tissue sections through NTS was examined by immunohistochemistry. The differential patterns of immunoreactivity in neuronal somata and dendrites of NTS neurons were generally in agreement with the PCR results, confirming that mRNA expression is correlated with receptor protein synthesis. At ultrastructural level, α1, α3, β2/3, and γ2 subunits were localized in both cytoplasmic and subsynaptic sites, the latter often apposed to GABA immunoreactive synapses. These results suggest that ionotropic receptors comprising the α1, α3, β2/3, and γ2 may mediate inhibitory GABA responses in the NTS.

Nitric oxide producing neurones in the rat medulla oblongata that project to nucleus tractus solitarii

The production of nitric oxide in neurones of the rat medulla oblongata that project to the nucleus tractus solitarii (NTS) was examined by simultaneous immunohistochemical detection of nitric oxide synthase (NOS) and of cholera toxin B-subunit (CTb), which was injected into the caudal zone of the NTS. Neurones immunoreactive for CTb and neurones immunoreactive for NOS were widely co-distributed and found in almost all the anatomical divisions of the medulla. Dual-labelled cells, containing both CTb and NOS immunoreactivities were more numerous ipsilaterally to the injection sites. They were concentrated principally in the more rostral zone of the NTS, raphé nuclei, dorsal, intermediate and lateral reticular areas, spinal trigeminal and paratrigeminal nuclei and the external cuneate and medial vestibular nuclei. Isolated dual-labelled neurones were also scattered throughout most of the divisions of the reticular formation. These observations indicate that many areas of the medulla that are known to relay somatosensory and viscerosensory inputs contain NOS immunoreactive neurones that project to the NTS, and may, therefore, contribute to the dense NOS-immunoreactive innervation of the NTS. The release of nitric oxide from the axon terminals of these neurones may modulate autonomic responses generated by NTS neurones in relation to peripheral sensory stimuli, and thus ultimately regulate sympathetic and/or parasympathetic outflow.

Rhombex‐29, a novel gene of the PLP/DM20‐M6 family cloned from rat medulla oblongata by differential display

Rhombex‐29, a novel gene of the PLP/DM20‐M6 family cloned from rat medulla oblongata by differential display

The effects of the mediodorsal nucleus of the thalamus on respiratory neurons of the medulla oblongata and respiration in rats in conditions of hypoxia.

The effects of the associated mediodorsal nucleus of the thalamus on spike activity of respiratory neurons in the medulla oblongata and on respiration were studied in normal conditions and in oxygen insufficiency. At normal atmospheric pressure, before animals were elevated to low pressures, electrical stimulation of the mediodorsal nucleus of the thalamus had predominantly inhibitory effects. At the initial phase of hypoxia, at a "height" of 4,000-5,000 m, hypoxic activation of neuron discharge frequency occurred. with an increase in the frequency of respiration. In these conditions, the inhibitory effect of stimulation of the mediodorsal nucleus of the thalamus was less marked than in normoxic conditions. The opposite effect occurred at the second phase of hypoxia (7,500-8,000 m)-inhibition of activity in the medulla oblongata and thalamic center. In severe hypoxia, there was inhibition of neuron spike activity and a decrease in the frequency of respiration, which became superficial; in these conditions, the inhibitory effect of the thalamus was insignificant.

Immunohistochemical localization of substance P receptors in the midline glia of the developing rat medulla oblongata with special reference to the formation of raphe nuclei

Immunohistochemical localization of the substance P receptor (SPR) was examined in the developing rat medulla oblongata, with special reference to the development of substance P (SP)-immunoreactive neurons which form the medullary raphe nuclei. During development, SPR immunoreactivity was detected in cells lying lateral to the medullary midline from embryonic day 13 (E13) to postnatal day 5 (P5). The SPR-positive cell bodies were located close to the fourth ventricle, and bore long processes extending to the ventral pial surface. This SPR immunoreactivity co-localized with staining for monoclonal antibody 1D11, a specific marker of immature astrocytes. Substance P (SP)-immunoreactive neurons were first detected at E14 in the ventrolateral part of the medulla. By E16 their number had increased and they were arrayed in two rows closely parallel to the SPR-immunoreactive processes of non-neuronal cells. By P1, two separate SP-immunoreactive cell clusters could be recognized at the midline, representing dorsally the nascent raphe pallidus and ventrally the raphe obscurus. In addition, many SP-immunoreactive fibers traveled rostrocaudally in the medulla oblongata, juxtaposed to the midline sheets of SPR-immunoreactive long processes. SPR-immunoreactive processes at the midline were also immunoreactive for S-100, a glia-specific calcium-binding protein that is known to promote axonal growth of raphe neurons. These results suggest that SPR-expressing immature glial cells at the medullary midline are involved in the development of SP-immunoreactive raphe neurons, both in the formation of the medullary raphe nuclei and in axon guidance and growth.

Distribution of dopamine-immunoreactive fibers in the rat brainstem

We describe the distribution of axons immunoreactive for dopamine in pons and medulla oblongata of rat under normal conditions or after inhibition of monoamine oxidase or dopamine β-hydroxylase. In the pons of non-treated animal, fairly dense plexuses of dopamine-immunoreactive varicose fibers were found in the locus coeruleus, dorsal parabrachial and dorsal raphe nuclei, central gray and reticular formation dorsal to the superior olive. In the medulla oblongata, the immunoreactive fibers were abundant in the dorsal vagal complex, lateral paragigantocellular nucleus, midline raphe nuclei and spinal trigeminal nucleus. Monoamine oxidase inhibition made it possible to increase the intensity of immunoreactivity and consequently the number of labeled fibers in these areas, indicating that dopamine is perpetually oxidized by monoamine oxidase, and consequently in low concentration under normal conditions. Sparse dopamine-immunoreactive fibers were observed in the pontine gray, motor trigeminal nucleus, inferior olive and major axon bundles such as the dorsal and ventral tegmental bundles, where numerous noradrenergic fibers have been reported. In axons of these areas, intense dopamine-immunoreactivity was seen only after inhibition of dopamine-β-hydroxylase. It appears that dopamine is released and oxidized in response to autonomic changes such as hypoxia, hemorrhage, and cardiovascular variation in the caudal brainstem, as we have described elsewhere.

Effects of β-Endorphin on Norepinephrine Release in Hypertension

Recent studies have suggested an involvement of the endogenous opioid system in blood pressure control. The purpose of the present study was to determine the role of beta-endorphin in the regulation of sympathetic nervous activity in the central nervous system of hypertension. The effects of beta-endorphin on the electrically evoked release of [3H]norepinephrine (NE) were investigated in superfused slices of rat medulla oblongata. Beta-endorphin inhibited the stimulation-evoked NE release in a dose-dependent manner in rat medulla oblongata. In the medulla oblongata of spontaneously hypertensive rats (SHR), the inhibitory effect of beta-endorphin on the stimulation-evoked NE release was significantly smaller than in the medulla oblongata of Wistar-Kyoto rats. These results showed that beta-endorphin might reduce NE release in rat medulla oblongata. Furthermore, the lesser inhibitory effect of beta-endorphin on NE release in SHR might suggest that the opioid peptide could be involved in the regulation of central sympathetic nervous activity in hypertension.

Amylin compared with calcitonin: competitive binding studies in rat brain and antinociceptive activity

Binding studies for rat amylin (AMY) and salmon calcitonin (sCT) were performed on rat membranes prepared from pons and medulla oblongata of rats. The aim was to see whether specific binding sites for AMY and/or for sCT present in these areas could be relevant to some of the biological activities of the two peptides. Binding sites specific for [ 125 I ]AMY are present in the pons-medulla of rat brain as AMY, but not sCT, was able to displace radiolabeled AMY binding with an IC 50=3.7±0.5×10 −10 M. In contrast, binding of [ 125 I ]sCT was displaced by both sCT and AMY, although with different potencies, the IC 50 for sCT being 1±0.1×10 −11 M, and for AMY, 1.8±0.08×10 −7 M. The functional significance of the presence of these binding sites was evaluated in two different nociceptive tests, hot-plate and tail-flick. In the tail-flick test neither AMY (5–10 μg/rat, i.c.v.) nor sCT (10 μg/rat i.c.v.) showed antinociceptive activity, whereas in the hot-plate test AMY (10 μg/rat, i.c.v.) significantly increased the response latencies as did sCT (250 ng/rat, i.c.v.). These results demonstrated that a 40-fold greater dose of AMY is necessary to produce a comparable antinociceptive effect to that exerted by sCT. These findings are in accordance with the low affinity of AMY for sCT binding sites in rat pons-medulla. It is therefore suggested that the central inhibitory activity of AMY on pain perception involves interaction with sCT receptors whereas the selective AMY binding sites subserve other (as yet unknown) functions.

Rhombex-29, a novel gene of the PLP/DM20-M6 family cloned from rat medulla oblongata by differential display.

The ventral medullary surface (VMS) is known as the site of the central chemosensitive neurons. These neurons sense excess CO(2)/H(+) dissolved in the cerebrospinal fluid that superfuses the VMS and induce hyperventilation. We hypothesized that genes specific for hyperventilation are expressed much more highly in VMS neurons than in extra-VMS neurons in other parts of the central nervous system (CNS). Applying the differential display technique to the brain of adult rats, we differentiated the mRNAs of the VMS neurons from those of cerebral cortex neurons. Seventeen candidate clones were selected, and their sequences were analyzed. Among these 17 clones, one encodes a novel four-transmembrane protein, which we named rat Rhombex-29. Structural analysis and the phylogenic tree showed that rat Rhombex-29 is homologous to the major CNS myelin protein PLP/DM20-M6 family and belongs to the intermediate type between mouse M6b and shark DMgamma. As the embryos grew into adult rats, constant expression of rat Rhombex-29 mRNA was found in the brain. Hypercapnic stimulation increased expression of rat Rhombex-29 mRNA in the VMS neurons but not in the cerebral cortex neurons. These results indicate that the VMS neurons are endowed with a novel gene, rat Rhombex-29, that is sensitive to H(+).

Respiratory pacemaker cells responsive to CO(2) in the upper medulla: dose response and effects of mediators.

We previously reported on the presence of respiratory pacemaker cells that are highly sensitive to CO(2), in a region of the medulla oblongata in the fetal rat, 2 mm rostral to the obex. We now report on the CO(2) dose responses of these cells, as well as their responsiveness to certain chemical agents known to affect breathing in the fetus. Twenty-day-old fetal Sprague Dawley rats were block-dissected, and the cells of target areas were dissociated as previously described. Neuronal cells were plated on a medullary background and placed in the incubator with 10% CO(2) for 2-3 weeks. Cells were then studied using patch-clamp techniques. Pacemaker cells with single or bursting potentials showed responsiveness to CO(2) starting with pulses of 10 msec. Irregular beating or silent cells had poor or absent responsiveness to CO(2). Pacemaker cells responded to norepinephrine with increased firing potential; this action was blocked by metropolol. PGE(2) had no effect on pacemaker-cell activity, but indomethacin increased the spike frequency from 336+/-41 to 384+/- 65 spikes/min. Morphine stimulated the pacemaker cells from 205+/-25 to 272+/-29 spikes/min; this was blocked by naloxone. Finally, a placental extract, which inhibited breathing in the unanesthetized fetal sheep preparation, increased the activity of pacemaker cells from 301+/-35 to 452+/-52 spikes/min. In all of the above, irregular beating cells responded poorly and silent cells did not respond. The findings indicate that these pacemaker cells are uniquely designed to respond to CO(2) and have some properties which allow them to respond to certain chemical mediators in a manner similar to that of the whole respiratory system in vivo.

Influence of Clitoria Ternatea Extracts on Memory and Central Cholinergic Activity in Rats

Clitoria ternatea , commonly known as Shankpushpi, is widely used in the traditional Indian system of medicine as a brain tonic and is believed to promote memory and intelligence. We examined the effectiveness of alcoholic extracts of aerial and root parts of C. ternatea at 300 and 500 mg/kg doses orally in rats in attenuating electroshock-induced amnesia. Extracts at 300 mg/kg dose produced significant memory retention, and the root parts were found to be more effective. In order to delineate the possible mechanism through which C. ternatea elicits the anti-amnesic effects, we studied its influence on central cholinergic activity by estimating the acetylcholine content of the whole brain and acetylcholinesterase activity at different regions of the rat brain, viz., cerebral cortex, midbrain, medulla oblongata and cerebellum. Our results suggest that C. ternatea extracts increase rat brain acetylcholine content and acetyl cholinesterase a ctivity in a similar fashion to the standard cerebro protective drug Pyritinol.

Hypotension activates neuropeptide Y-containing neurons in the rat medulla oblongata

The present study was designed to determine whether neurons within cardiovascular control nuclei of the rat brainstem that become activated following a hypotensive insult also possess the capacity to utilize neuropeptide Y. Adult male Wistar–Kyoto rats were injected with glyceryl trinitrate (10 mg/kg, i.p.) or vehicle, and 4 h later anaesthetized (pentobarbitone, 60 mg/kg, i.p.) and transcardially perfused. The brains were removed and processed by standard two-colour peroxidase immunohistochemistry. Activated cells were determined by incubation with a primary antibody to Fos protein, which was followed by a second incubation with a primary antibody to neuropeptide Y for double labelling of Fos-positive cells. Compared to vehicle, glyceryl trinitrate-induced hypotension caused a marked induction of Fos protein in the caudal one-third of the nucleus tractus solitarius (bregma −14 to −13.3 mm), which tailed off rapidly in more rostral sections. Following hypotension, significant populations of activated cells were also observed in the rostral and caudal ventrolateral medulla. In the caudal nucleus tractus solitarius and the posterior part of the medial nucleus tractus solitarius, respectively, 15 of 104 and 40 of 120 Fos-positive cells exhibited cytoplasmic neuropeptide Y immunoreactivity following hypotension, compared to seven of 40 and 15 of 40 in vehicle-treated rats, indicating a significant (two- to three-fold) increase in double-labelled cells following systemic glyceryl trinitrate ( P<0.05, unpaired t-test). In contrast, in the anterior part of the medial nucleus tractus solitarius, the number of double-labelled cells did not change following hypotension. An increase in double-labelled cells was also observed in the rostral ventrolateral medulla (2.5-fold increase compared to vehicle) and caudal ventrolateral medulla (5.8-fold increase compared to vehicle) following hypotension. These data indicate that, in the rat, neuropeptide Y-containing neurons are involved in the central response to a hypotensive challenge. The primary regions where neuropeptide Y-containing neurons appear to be activated are the caudal one-third of the nucleus tractus solitarius and the caudal ventrolateral medulla/rostral ventrolateral medulla, which are key nuclei associated with the integration of the baroreceptor heart rate reflex and sympathetic vasomotor outflow.