孤束核参与室旁核加压素能神经元对大鼠胃缺血-再灌注损伤的调控作用

目的：探讨孤束核（NTS）在下丘脑室旁核（PVN）加压素能神经元对大鼠胃缺血-再灌注损伤（GI-RI）调控中的作用。方法：复制夹闭大鼠腹腔动脉30 min，松开动脉夹血流复灌1 h的GI-RI模型，观察核团内微量注射、电刺激、损毁等对其影响。结果：PVN内注射精氨酸加压素（AVP）能明显减轻GI-RI，且具有剂量-效应依赖关系（r=-0.477, P<0.05）；损毁双侧NTS或NTS内给予AVP受体阻断剂均能取消电刺激PVN对GI-RI的减轻作用；NTS内注射AVP的作用与PVN内注射AVP的效应相似。结论：NTS参与下丘脑室旁核加压素神经元对大鼠胃缺血-再灌注损伤的调控作用，并且是通过其中的AVP受体来实现的。     

Losartan blocks the excitatory effect of peripheral hypertonic stimulation on vasopressinergic neurons in hypothalamic paraventricular nucleus in rats: electrophysiological and immunocytochemical evidence

The effect of peripheral hypertonic stimulation on the neurons of hypothalamic paraventricular nucleus (PVN) was investigated in the present study with both electrophysiological and immunocytochemical methods. The discharge frequency of the neurons with phasic activity in PVN could be increased by intraperitoneal (i.p.) injection of hypertonic saline (HS, 1.5M NaCl) (from 2.8 +/- 0.5 Hz to 5.4 +/- 0.9 Hz, P<0.001). The Fos expression in PVN could be enhanced (from 21.2 +/- 12.9 to 217.3 +/- 38.5 Fos-positive neurons, P<0.001) by i.p. HS and the majority of AVP-positive neurons expressing Fos (91.7 +/- 3.6%) was in magnocellular subdivision of PVN. After intracerebroventricular (i.c.v.) injection of losartan, angiotensin II type 1 (AT1) receptor antagonist (5 microg/microl), the excitatory effect of peripheral hypertonic stimulation on PVN neurons with phasic activity was inhibited significantly, and the number of the neurons co-expressing Fos and AVP in PVN decreased significantly (P<0.001) as well. The result demonstrated that the vasopressinergic neurons in PVN could be excited by peripheral hypertonic stimulation, and this excitation might be mediated by angiotensin II fibers projecting from subfornical organ to PVN.     

Activation within dorsal medullary nuclei following stimulation in the hypothalamic paraventricular nucleus in rats

The influence of the hypothalamic paraventricular nucleus (PVN) on neurones in the dorsal medulla has been examined in 71 urethane/sagatal-anaesthetised rats. Of 536 neurones localised and tested for responses to electrical stimulation of both the vagus and/or the PVN, 378 were synaptically or antidromically activated following vagal stimulation 72 of which were synaptically activated by stimulation within PVN. The majority of those were located at the border between NTS and dorsal motor nucleus of the vagus in caudal NTS. None showed cardiac or ventilatory rhythm. Neurones showing such rhythms were not affected from PVN. Of 89 neurones in dorsal motor nucleus of the vagus, ten were synaptically activated and two synaptically depressed from PVN. PVN activated neurones in NTS tested for responses to stimulation of arterial baroreceptors and carotid body chemoreceptors were either unaffected or inhibited, but gastric inflation excited them. The results suggest a powerful PVN influence on the dorsal medulla, which is largely confined to the ventral and caudal NTS. There is little evidence for an effect on neurones with a cardiovascular function, but the abdominal vagal influence suggests a link with feeding.     

Role of nucleus tractus solitarius 5-HT3 receptors in the defense reaction-induced inhibition of the aortic baroreflex in rats

Different stressful conditions elicit a typical behavior called the defense reaction. Our aim was to determine whether 5-HT3 receptors in the nucleus tractus solitarius (NTS) are involved in 1) the inhibition of the baroreflex bradycardia and 2) the rise in blood pressure, which are known to occur during the defense reaction. In urethane-anesthetized rats, the defense reaction was elicited by electrical stimulation of the dorsomedial nucleus of the hypothalamus (DMH) or the dorsal part of the periaqueductal gray (dPAG). Direct electrical stimulation of the aortic depressor nerve was used to trigger the typical baroreflex responses. Aortic stimulation at high (100-150 microA) and low (50-90 microA) intensity produced a decrease in heart rate of -39 to -44% (relative to baseline, Group 1 responses, n = 113) and -19 to -24% (Group 2 responses, n = 43), respectively. In spontaneously breathing rats, Group 1 and Group 2 bradycardiac responses were inhibited during DMH (-75 +/- 4% and -96 +/- 4%, n = 38 and n = 11, respectively), as well as dPAG (-81 +/- 3% and -95 +/- 4%, n = 36 and n = 10, respectively) stimulation. The aortic baroreflex bradycardia was hardly affected by DMH or dPAG stimulation when bicuculline (5 pmol), a specific GABAA receptor antagonist, had previously been microinjected into the NTS. Likewise, NTS microinjections of granisetron, a specific 5-HT3 receptor antagonist, prevented, in a dose-dependent manner, the baroreflex bradycardia inhibition. In addition, intra-NTS granisetron did not affect the rise in blood pressure induced by either site stimulation. These data show that 5-HT3 receptors in the NTS are involved in the GABAergic inhibition of the aortic baroreflex bradycardia, but not in the rise in blood pressure, occurring during the defense reaction elicited by DMH or dPAG stimulation.     

Inhibition by locus coeruleus on the baroreceptor reflex response in the rat.

We evaluated the modulation of baroreceptor reflex (BRR) response by locus coeruleus (LC) in adult, male Sprague-Dawley rats anesthetized with urethane (1.5 g/kg, i.p.). Under an electrical stimulation condition that did not appreciably alter the basal systemic arterial pressure and heart rate, the LC significantly suppressed the BRR response. Microinjection of L-glutamate (1 nmol, 50 nl) into the LC essentially duplicated this depressant effect. Intracerebroventricular (i.c.v.) administration of the alpha 1-adrenoceptor antagonist, prazosin (6.5 nmol), appreciably blunted the inhibition by LC on the BRR response. Yohimbine (6.5 nmol), the alpha 2-adrenoceptor blocker, however, was ineffective. Direct microinjection of prazosin (50 pmol), but not yohimbine (50 pmol), into the terminal site of baroreceptor afferents at the nucleus tractus solitarii (NTS) also significantly blunted the suppressive effect of LC on the BRR response. These results suggest that the LC may produce an inhibition on the BRR response by a process that involves the alpha 1-adrenoceptors located in the NTS.     

Differential neuronal activation in the hypothalamic paraventricular nucleus and autonomic/neuroendocrine responses to I.C.V. endotoxin

The paraventricular nucleus (PVN) of the hypothalamus is a key site for regulating neuroendocrine and autonomic activities. To study the role of the PVN activation in brain inflammation-induced autonomic/endocrine responses, lipopolysaccharide (LPS; 0.5 or 5 microg) was administered i.c.v. and rats were killed 1, 3 or 6 h after the injection. I.c.v. LPS-0.5 microg did not cause changes in mean arterial pressure (MAP) over 6 h, whereas LPS-5 micro induced a temporary decrease in MAP approximately 30 min after the injection. LPS at either dose increased heart rate. Whereas induction of Fos-like immunoreactivity was confined to the dorsal medial parvocellular division (mpd) of the PVN with the lower dose, labeling was found throughout the PVN with the higher dose. At 3 h, LPS-5 microg also stimulated increases in arginine vasopressin (AVP) heteronuclear RNA levels in the posterior magnocellular and dorsal parvocellular divisions of the PVN at 3 h, and activation of catecholaminergic neurons in the hypothalamus and brainstem. Increases in tyrosine hydroxylase (TH) mRNA levels were found in the locus coeruleus at 6 h. LPS at both doses elevated plasma ACTH levels and corticotropin-releasing factor gene expression in the mpd of the PVN. I.c.v. LPS induced IL-1beta mRNA in the meninges and ventricular ependymal lining at 1 h, and in the periventricular PVN at 3 h. Induction of IL-1beta mRNA was found in the lung at 1 h, and a significant increase in plasma LPS binding protein occurred at 3 h.These findings suggest that PVN activation induced by the lower dose of LPS is related primarily to increases in activity of the HPA axis, whereas the higher dose of LPS more widely activates autonomic regulatory centers including the PVN and also stimulates changes in sympathetic output and hypothalamic AVP synthesis. Activation of the PVN by i.c.v. LPS likely occurs through both central and systemic routes. Differential neuronal activation in the PVN is functionally related to autonomic/endocrine responses elicited by brain inflammation.     

Cardiovascular function of a glutamatergic projection from the hypothalamic paraventricular nucleus to the nucleus tractus solitarius in the rat

Experiments were done in urethane-anesthetized, barodenervated, male Wistar rats. Chemical stimulation of the hypothalamic paraventricular nucleus (PVN) by unilateral microinjections of N-methyl-d-aspartic acid (NMDA) elicited increases in mean arterial pressure (MAP) and greater splanchnic nerve activity (GSNA). The increases in the MAP and GSNA induced by chemical stimulation of the PVN were significantly exaggerated by bilateral microinjections of d(−)-2-amino-7-phosphono-heptanoic acid (d-AP7) and 2,3-dioxo-6-nitro-1,2,3,4-tetrahydro-benzo[f]quinoxaline-7-sulfonamide disodium (NBQX) (ionotropic glutamate receptor antagonists) into the medial subnucleus of the nucleus tractus solitarius (mNTS). These results were confirmed by single unit recordings; i.e. excitation of mNTS barosensitive neurons caused by chemical stimulation of the ipsilateral PVN was blocked by application of d-AP7 and NBQX to these neurons. Bilateral microinjections of d-AP7 and NBQX into the mNTS elicited pressor responses which were significantly attenuated by inhibition of PVN neurons by bilateral microinjections of muscimol. Unilateral microinjections of fluorogold into the mNTS resulted in bilateral retrograde labeling of the PVN neurons. Unilateral microinjections of biotinylated dextran amine into the PVN resulted in anterograde labeling of axons and terminals in the mNTS bilaterally and the labeled terminals exhibited vesicular glutamate transporter-2 immunoreactivity. These results indicated that 1) a tonically active glutamatergic bilateral projection from the PVN to the mNTS exists; 2) bilateral blockade of ionotropic glutamate receptors in the mNTS exaggerates the increases in MAP and GSNA, but not heart rate, to the chemical stimulation of the PVN; and 3) this projection may serve as a restraint mechanism for excitatory cardiovascular effects of PVN stimulation.     

Effects of hypothalamic stimulation on activity of dorsomedial medulla neurons that respond to subdiaphragmatic vagal stimulation

1. Effects of hypothalamic stimulation on activity of dorsomedial medulla neurons that responded to subdiaphragmatic vagal stimulation were investigated in urethan-anesthetized rats. 2. Extracellular recordings were made from 231 neurons in the nucleus of the tractus solitarius (NTS) that fired repetitively in response to single-pulse subdiaphragmatic vagal stimulation and from 320 neurons in the dorsal motor nucleus of the vagal nerve (DMV) that responded antidromically to subdiaphragmatic vagal stimulation. The mean latencies of responses to subdiaphragmatic vagal stimulation were 90.3 +/- 17.1 ms (mean +/- SD) for NTS neurons, and 90.8 +/- 11.2 ms for DMV neurons. This indicated that both afferent and efferent subdiaphragmatic vagal fibers were thin and unmyelinated and had a conduction velocity of approximately 1 m/s. 3. In extracellular recordings from 320 DMV neurons, marked inhibition preceded the antidromic response and subdiaphragmatic vagal stimulation evoked orthodromic spikes in only a few neurons. 4. Intracellular recordings from 66 DMV neurons revealed inhibitory postsynaptic potentials (IPSPs) before the antidromic responses. These IPSPs suppressed spontaneous firing and prevented excitatory postsynaptic potentials (EPSPs) from generating action potentials. 5. Stimulation in all hypothalamic loci studied, the ventromedial hypothalamic nucleus (VMH), the lateral hypothalamic area (LHA), and the paraventricular nucleus (PVN), induced responses with similar characteristics of excitation alone or excitation followed by inhibition in most NTS and DMV neurons. 6. No reciprocal effect of VMH and LHA stimulation was observed on NTS and DMV neurons. 7. Intracellular recordings from DMV neurons revealed monosynaptic EPSPs in response to stimulation of the VMH, the LHA, and the PVN. 8. PVN stimulation evoked significantly more responses in NTS and DMV neurons than VMH stimulation and more responses in DMV neurons than LHA stimulation. This suggests a difference in the number of connections between each hypothalamic site and the dorsomedial medulla. 9. The same dorsomedial medulla neurons were tested with VMH and LHA stimulation. The respective mean latencies of the antidromic and the orthodromic NTS neuron responses were 37.3 +/- 3.2 and 39.6 +/- 12.9 ms for VMH stimulation and 29.8 +/- 5.3 and 31.8 +/- 8.7 ms for LHA stimulation. The mean latencies of the orthodromic DMV neuron responses were 39.4 +/- 8.3 ms for VMH stimulation and 31.1 +/- 5.2 ms for LHA stimulation. The estimated conduction velocity from the VMH to the dorsomedial medulla was approximately 0.25 m/s and from the LHA it was approximately 0.33 m/s, which was significantly faster.(ABSTRACT TRUNCATED AT 400 WORDS)     

Catecholamine synapses and contents in the paraventricular hypothalamic nucleus and nucleus tractus solitarius of DOCA-salt hypertensive rats

Central catecholamine (CA) neurons in the nucleus tractus solitarius (NTS) and paraventricular hypothalamic nucleus (PVN) were studied in Wistar rats that had been unilaterally nephrectomized. The experimental animals were then treated with deoxycorticosterone acetate (DOCA) and salt water. The control animals were treated with the vehicle and tap water. Blood pressure of animals 4 weeks after DOCA/salt treatment was significantly elevated when compared to control rats. Morphologically, CA terminals showed no noticeable changes in the DOCA/salt hypertensive rats. Furthermore, the density of CA terminals either in the NTS or in the PVN of the DOCA/salt hypertensive rats was not statistically different from that of normotensive controls, suggesting that salt does not cause lesions or destruction of CA terminals. However, an extensive electron-microscopic morphometric analysis indicated that there was an enhancement of CA synaptogenesis (expressed by increased synaptic frequency among all CA boutons labeled with 5-hydroxydopamine) in the PVN, but not in the NTS of DOCA/salt hypertensive rats. In addition, the high-performance liquid chromatography revealed decreased CA contents in the PVN, but not in the NTS, of DOCA/salt hypertensive animals. Since synapses are primary sites for neurotransmitter release, the above results collectively suggest that more CA synapses formed in the PVN may reflect a net CA release from CA terminals resulting in the decreased CA content in the axonal terminals. Such an increased CA release and enhanced CA synaptogenesis may consequently enhance CA function in the PVN of hypertensive rats 4 weeks after DOCA/salt treatment, and relate to the development and/or maintenance of hypertension in the DOCA/salt rats.     

Right atrial stretch activates neurons in autonomic brain regions that project to the rostral ventrolateral medulla in the rat

Activation of the cardiac mechanoreceptors results in changes in sympathetic nerve activity and plays an important role in the responses elicited by elevated blood volume. Stimulation of the reflex influences several key autonomic regions, namely the paraventricular nucleus (PVN), the nucleus of the tractus solitarius (NTS) and the caudal ventrolateral medulla (CVLM). Neurons in these regions project directly to the rostral ventrolateral medulla (RVLM), a critical region in the generation of sympathetic vasomotor tone. The aim of the present experiments was to determine whether neurons in the PVN, NTS and CVLM that are activated by cardiac mechanoreceptor stimulation also project to the RVLM. Animals were prepared, under general anesthesia, by microinjection of a retrogradely transported tracer into the pressor region of the RVLM, and the placement of a balloon-tipped cannula at the junction of the right atrium and the superior vena cava. On the experimental day, in conscious rats, the balloon was inflated to stimulate cardiac mechanoreceptors (n = 9), or left uninflated (control, n = 8). Compared with controls, there was a significantly increased number of Fos-immunoreactive neurons (a marker of activation) in both the PVN (2.5-fold) and NTS (two-fold), but this was not seen in the CVLM. Compared with controls, a significant number of the neurons in the PVN (8%) and NTS (4.0%) that projected to the RVLM were activated. The data suggest that subgroups of RVLM-projecting neurons located in the PVN and NTS are involved in the central reflex pathway activated by cardiac mechanoreceptor stimulation.     

Glucocorticoid modulation of atrial natriuretic peptide, oxytocin, vasopressin and Fos expression in response to osmotic, angiotensinergic and cholinergic stimulation

The regulation of fluid and electrolyte homeostasis involves the participation of several neuropeptides and hormones that utilize hypothalamic cholinergic, alpha-adrenergic and angiotensinergic neurotransmitters and pathways. Additionally, it has been suggested that hypothalamus-pituitary-adrenal axis activity modulates hormonal responses to blood volume expansion. In the present study, we evaluated the effect of dexamethasone on atrial natriuretic peptide (ANP), oxytocin (OT) and vasopressin (AVP) responses to i.c.v. microinjections of 0.15 M and 0.30 M NaCl, angiotensin-II (ANG-II) and carbachol. We also evaluated the Fos protein immunoreactivity in the median preoptic (MnPO), paraventricular (PVN) and supraoptic (SON) nuclei. Male Wistar rats received an i.p. injection of dexamethasone (1 mg/kg) or vehicle (0.15 M NaCl) 2 h before the i.c.v. microinjections. Blood samples for plasma ANP, OT, AVP and corticosterone determinations were collected at 5 and 20 min after stimulus. Another set of rats was perfused 120 min after stimulation. A significant increase in plasma ANP, OT, AVP and corticosterone levels was observed at 5 and 20 min after each central stimulation compared with isotonic saline-injected group. Pre-treatment with dexamethasone decreased plasma corticosterone and OT levels, with no changes in the AVP secretion. On the other hand, dexamethasone induced a significant increase in plasma ANP levels. A significant increase in the number of Fos immunoreactive neurons was observed in the MnPO, PVN and SON after i.c.v. stimulations. Pre-treatment with dexamethasone induced a significant decrease in Fos immunoreactivity in these nuclei compared with the vehicle. These results indicate that central osmotic, cholinergic, and angiotensinergic stimuli activate MnPO, PVN and SON, with a subsequent OT, AVP, and ANP release. The present data also suggest that these responses are modulated by glucocorticoids.     

GABA may function tonically via GABA(A) receptors to inhibit hypotension and bradycardia by L-DOPA microinjected into depressor sites of the nucleus tractus solitarii in anesthetized rats

We have proposed that DOPA is a transmitter of the primary baroreceptor afferents terminating in the rat nucleus tractus solitarii (NTS). GABA is a putative inhibitory neuromodulator for baroreflex inputs in the NTS. GABA may inhibit DOPAergic transmission. Drugs were microinjected into depressor sites of the NTS in anesthetized rats. DOPA (10-60 ng) elicited dose-dependent depressor responses. GABA (3-300 ng) elicited dose-dependent pressor responses. Nipecotic acid (100 ng) elicited pressor responses. Bicuculline (10 ng) elicited depressor responses. Responses to DOPA (30 ng) were inhibited by pretreatment with GABA and nipecotic acid, but potentiated by bicuculline, when vascular responses to pretreated drugs returned to basal levels. DOPA ME, a competitive DOPA antagonist, did not displace specific [3H]GABA binding. Prior DOPA ME (1 microg) inhibited by one-half pressor responses to 300 ng GABA. GABA seems to inhibit tonically via GABA(A) receptors depressor responses to DOPA and to elicit pressor responses partially by inhibition of tonic function of endogenous DOPA to activate depressor sites in the NTS. These findings further support the above proposal.     

Cholinergic input to the supraoptic nucleus increases Fos expression and body temperature in rats

To examine the role played by cholinergic input and processes in the supraoptic nucleus (SON) in the control of body temperature and water intake in rats, we used microdialysis to stimulate and analyze SON without disturbing the behavior of unanesthetized rats. After microdialysis, we also investigated immunoreactivity for c-Fos protein in the brain as an index of neuronal activation. Stimulation with neostigmine, an acetylcholine esterase inhibitor, through the microdialysis probe increased the extracellular concentration of acetylcholine in the SON. This cholinergic stimulation dose-dependently increased body temperature but did not significantly change the water intake. The stimulation markedly increased c-Fos-like immunoreactivity (Fos-IR) in the SON and certain hypothalamic areas, including the paraventricular nucleus (PVN) and median preoptic nucleus (MnPO). Fos-IR was also evident in certain regions of the pons and brainstem, including the locus ceruleus (LC), area postrema (AP), and nucleus of the solitary tract (NTS). Addition of atropine, a muscarinic receptor antagonist, to the dialysis medium containing neostigmine attenuated the increase of Fos-IR and suppressed the neostigmine-induced responses in body temperature. These results suggest that cholinergic input and activation of the muscarinic cholinoceptive neurons in the SON contribute to the regulation of body temperature. Activation of noradrenergic pathways in the brainstem including LC and NTS may be involved in the thermoregulation mechanism.     

Involvement of central beta-adrenoceptors in the tachycardia induced by water immersion stress in rats

The purpose of the present study was to investigate whether central beta-adrenoceptors are involved in stress-induced cardiovascular responses in rats. Using a biotelemetry system, blood pressure and heart rate were measured at rest and during stress induced by immersion in 1 cm-deep water. Intracerebroventricular (i.c.v.) injections of a nonselective beta-adrenoceptor antagonist, DL-propranolol (5 or 50 microg), significantly and dose dependently attenuated the tachycardia induced by water immersion stress (drug-induced reduction of tachycardia at 5 min after the start of stress: 61.4 +/- 13.2% for 5 microg, 72.5 +/- 8.2% for 50 microg). The same doses of DL-propranolol had no effect on the resting heart rate. Injection (i.c.v.) of a lower dose (5 microg) of D-propranolol--which has a lower potency as a beta-adrenoceptor antagonist than DL-propranolol, but a similar local anesthetic, membrane-stabilizing activity--did not attenuate the stress-induced tachycardia, although a higher dose (50 microg) did. Intravenous administration of DL-propranolol (5 or 50 microg) significantly attenuated the stress-induced tachycardia (drug-induced reduction of tachycardia at 5 min after the start of stress: 20.0 +/- 7.5% for 5 microg, 42.4 +/- 3.4% for 50 microg). However, the attenuation was much smaller than in the i.c.v. DL-propranolol-injected group. The i.c.v. injection of the 50 microg dose of DL-propranolol significantly augmented both the resting blood pressure and the pressor response to water immersion stress, whereas the lower dose (5 microg) had no effect. The i.c.v. injection of 50 microg D-propranolol also augmented, although not significantly, the resting blood pressure and the pressor response to stress. These results suggest that central beta-adrenoceptors are involved in the tachycardia induced by water immersion stress in rats.     

NMDA receptor antagonism blocks the cardiovascular responses to microinjection of trans-ACPD into the NTS of awake rats

The possible interaction of glutamatergic metabotropic agonists and N-methyl- d -aspartate (NMDA) receptors was investigated in the nucleus tractus solitarii (NTS) of awake rats. The cardiovascular responses to unilateral microinjection of trans -1-amino-1,3-cyclopentanediocarboxylic acid ( trans -ACPD; 250 pmol/50 nL) into the NTS ( n = 8) produced hypotension (−64 ± 4 mmHg) and bradycardic (−206 ± 11 bpm) responses, which were blocked by previous microinjection of 2-amino-5-phosphonovaleric acid (AP-5; 10 nmol/50 nL), a selective antagonist of NMDA ionotropic receptors, into the same site. Intravenous injection of methyl-atropine blocked both the bradycardic and hypotensive responses to microinjection of trans -ACPD into the NTS, indicating that the hypotension was secondary to the intense bradycardic response. The data also showed that the bradycardic and hypotensive responses to microinjection of an NMDA agonist (10 pmol/50 nL) into the NTS were not affected by previous microinjection of α-methyl-4-carboxyphenylglycine (MCPG; 5 nmol/50 nL), a non-selective antagonist of metabotropic receptors. The results showing that the cardiovascular responses to microinjection of trans -ACPD into the NTS were blocked by AP-5 indicate that the responses to metabotropic agonists in the NTS involves NMDA receptors.     

Central cardiovascular effects of calcitonin gene-related peptide: interaction with noradrenaline in the nucleus tractus solitarius of rats

Summary The haemodynamic responses to microinjections of rat or human calcitonin gene-related peptide (CGRP) into the nucleus tractus solitarius (NTS) of rats were studied. 40 fmol rCGRP did not significantly modify cardiovascular parameters, but 0.2 pmol decreased blood pressure and heart rate (HR), whereas 2 pmol produced a pressor response with no effect on HR. hCGRP elicited a transient fall in blood pressure when administered at the highest dose (2 pmol), but had no effects when given at 0.2 pmol. A possible functional relationship with catecholamines was also investigated. The hypotensive response to 20 nmol noradrenaline (NA) was significantly modified by simultaneous administration of a low dose (40 fmol, ineffective alone) of rCGRP. When rCGRP (40 fmol) was coinjected simultaneously with an ineffective dose (10 pmol) of NA, a hypotensive response was observed. Our results provide evidence that rCGRP may play a role in the control of cardiovascular homeostasis in the NTS, and suggest a functional interaction between this peptide and NA.     

Paraventricular nucleus influence on renal sympathetic activity in vasopressin gene-deleted rats

In Wistar rats, an increase in renal sympathetic activity is induced by activation of presympathetic neurones in the paraventricular nucleus (PVN) and reflexly by a mild venous haemorrhage. Both stimuli are dependent on the release of vasopressin and glutamate at spinal synapses. The significance of the supraspinal pathway and the co-operative interaction of vasopressin with an excitatory amino acid is unclear. The present study examines this in Brattleboro rats, which have a natural vasopressin gene deletion. The responses were compared with Long-Evans rats, from which Brattleboro rats are derived. All rats were anaesthetized with a mixture of urethane (650 mg kg(-1) i.v.) and chloralose (50 mg kg(-1) i.v.). Recordings were made of blood pressure, heart rate and renal sympathetic nerve activity (RSNA). Microinjection of d,l-homocysteic acid (DLH, 0.2 m, 100 nl) at sites restricted to the PVN elicited significant increases in RSNA (P < 0.001) in both strains of rats. These changes were significantly reduced (P < 0.01) in Long-Evans rats by intrathecal application to the spinal cord of either a V(1a) antagonist or a glutamate antagonist (kynurenic acid), whereas in Brattleboro rats the changes were significantly reduced (P < 0.05) only by kynurenic acid. Removal of 1 ml of venous blood in Long-Evans rats increased RSNA by 28 +/- 4% (P < 0.01), which was significantly reduced (P < 0.05) by prior intrathecal application of either the V(1a) antagonist or by kynurenic acid. The same test in Brattleboro rats caused a significantly greater (P < 0.05) increase (63 +/- 14.7%) in RSNA which, in contrast to Long-Evans rats, was unchanged by intrathecal application of the V(1a) antagonist, being significantly reduced (P < 0.01) only by intrathecal kynurenic acid. Thus, in Brattleboro rats, the lack of vasopressin in the brain sympathetic pathways appears to be compensated, acutely, by glutamate-releasing pathways. This might indicate that, in normal rats, vasopressin is more important in maintaining longer term adjustments to stressors.     

Swallowing responses induced by microinjection of glutamate and glutamate agonists into the nucleus tractus solitarius of ketamine-anesthetized rats

Summary Swallowing is a patterned motor activity generated by neurons located within the nucleus tractus solitarius (NTS). An excitatory amino acid (EAA) neurotransmitter, such as glutamate (GLU), is suspected of being involved in the initiation of swallowing by NTS neuronal components. However, swallowing can still be elicited in animals anesthetized with ketamine, an antagonist of the N-methyl-D-aspartate (NMDA) subclass of EAA receptors. The present experiments were therefore designed to investigate the influence of EAA administration within the NTS on the swallowing motor acitivity of rats anesthetized with ketamine. Pressure microinjections of GLU in doses ranging from 25 to 500 pmol elicited swallowing. This effect was dose-dependent and was not reproduced when control injections of the vehicle solution were performed. Microinjections of the GLU agonists, quisqualate (QUIS) and NMDA, in doses ranging between 2.5 and 50 pmol, also induced swallowing motor activities. QUIS, like GLU, elicited a short series of swallows at a brief latency while NMDA generated long-lasting rhythmic swallowing with a longer latency. Swallowing induced by GLU microinjections (100 pmol) was suppressed almost completely by local pretreatment with either the broad spectrum EAA receptor antagonist, gamma-D-glutamylglycine (250 pmol), or the more selective non-NMDA antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (50–100 pmol), but not by pretreatment with the selective NMDA antagonist, DL-2-amino-5-phosponovalerate (250 pmol). On the other hand, pretreatment with DL-2-amino-5-phosphonovalerate (50 pmol) suppressed the deglutitions induced by NMDA microinjections (10 pmol) but not those elicited by QUIS microinjections (10 pmol). These results provide evidence that swallowing can be induced by activation of EAA receptors of both the NMDA and the non-NMDA subclasses located within the NTS. Furthermore they indicate that both subclasses may still be active in ketamine-anesthetized animals.     

Cardiovascular actions of adrenocorticotropin microinjections into the nucleus tractus solitarius of the rat

The presence of adrenocorticotropin (ACTH) containing cells and melanocortin (MC) receptors has been reported in the nucleus tractus solitarius (NTS) of the rat. The importance of the NTS in the regulation of cardiovascular function is also well established. Based on these reports, it was hypothesized that ACTH acting within the NTS may modulate the central regulation of cardiovascular function. To test this hypothesis, cardiovascular effects of ACTH in the NTS were investigated in intact urethane-anesthetized and unanesthetized decerebrate, artificially ventilated, adult male Wistar rats. Microinjections of ACTH (0, 0.5, 1, 2, and 4 mM) into the medial subnucleus of NTS (mNTS) elicited decreases in mean arterial pressure (MAP; 0+/-0, 24.4+/-3.5, 35.7+/-4.3, 44.5+/-5.8 and 53.7+/-5.6 mm Hg, respectively) and heart rate (HR; 0+/-0, 25.7+/-5.3, 35.5+/-6.4, 47.5+/-12.1 and 55.0+/-5.6 beats/min, respectively). The onset and duration of the responses to microinjections of ACTH (0.5-4 mM) were 5-10 s and 45-120 s, respectively. Control microinjections of artificial cerebrospinal fluid (aCSF) did not elicit any response. The volume of all microinjections was 100 nl. The concentrations of ACTH that elicited depressor and bradycardic responses when microinjected into the mNTS (e.g. 1 or 2 mM, 100 nl), did not elicit a response when injected i.v. (n=5) or i.c.v. (n=2) indicating that there was no leakage of the drug from the injection site in the mNTS. Microinjections of MC3/4 receptor antagonists (acetyl-[Nle(4), Asp(5), d-2-Nal(7), Lys(10)]-cyclo-alpha-MSH amide, fragments 4-10 (SHU9119) and agouti-related protein (83-132) amide) into the mNTS blocked the responses to ACTH. Microinjections of ACTH (2 mM) into the mNTS decreased efferent greater splanchnic nerve activity. Bilateral vagotomy significantly attenuated ACTH-induced bradycardia. These results indicated that: 1) microinjections of ACTH into the mNTS elicited depressor and bradycardic responses, 2) these responses were mediated via MC3/4 receptors, 3) the depressor effects were mediated via a decrease in the activity of the sympathetic nervous system, and 4) the bradycardic responses were vagally mediated.