Central autonomic activation by intracisternal TRH analogue excites gastric splanchnic afferent neurons.
Intracisternal (ic) injection of thyrotropin-releasing hormone (TRH) or its stable analogue RX 77368 influences gastric function via stimulation of vagal muscarinic pathways. In rats, the increase in gastric mucosal blood flow evoked by a low ic dose of RX 77368 occurs via release of calcitonin gene-related peptide from capsaicin-sensitive afferent neurons, most probably of spinal origin. In this study, the effect of low ic doses of RX 77368 on afferent impulse activity in splanchnic single fibers was investigated. The cisterna magna of overnight-fasted, urethan-anesthetized Sprague-Dawley rats was acutely cannulated, and fine splanchnic nerve twigs containing at least one fiber responsive to mechanical probing of the stomach were isolated at a site immediately distal to the left suprarenal ganglion. Unit mechanoreceptive fields were encountered in all portions of the stomach, both superficially and in deeper layers. Splanchnic afferent unit impulse activity was recorded continuously during basal conditions and in response to consecutive ic injections of saline and RX 77368 (15-30 min later; 1.5 or 3 ng). Basal discharge rates ranged from 0 to 154 impulses/min (median = 10.2 impulses/min). A majority of splanchnic single units with ongoing activity increased their mean discharge rate by >/=20% after ic injection of RX 77368 at either 1.5 ng (6/10 units; median increase 63%) or 3 ng (19/24 units; median increase 175%). Five units lacking impulse activity in the 5-min before ic RX 77368 (3 ng) were also excited, with the onset of discharge occurring within 1.0-5.0 min postinjection. In units excited by ic RX 77368, peak discharge occurred 15.6 +/- 1.3 min after injection and was followed by a decline to stable activity levels +info)
Circadian and other rhythmic activity of neurones in the ventromedial nuclei and lateral hypothalamic area.
1. The frequency of firing was simultaneously recorded from single neurones of the ventromedial nuclei (VMN) and the lateral hypothalamic area (LHA) in urethane anaesthetized rats for many hours. 2. There were circadian changes of VMN and LHA neurone activity. The pattern of this circadian rhythm is as follows: throughout the day LHA neurones show higher activity than that of VMN, as indicated by higher frequency and more fluctuations in their rates of firing. In late afternoon the discharge rate of LHA neurones increases further, showing oscillations of short duration. In the early evening hours LHA neurone activity gradually goes down, as the VMN neurones become active. Throughout the night, VMN neurones are more active than those of LHA, just the opposite of the day period. In early morning hours VMN neurones gradually become quiet, while LHA neurones begin to show activity. 3. Superimposed on the circadian rhythm, at certain periods of the day, VMN and LHA neurones showed short duration oscillations in rate of firing, roughly every 7-15 sec and every 3-5 min. 4. Activities in neurones of the VMN and LHA were reciprocally related; a decrease in firing rate of one was associated with an increase in the other. This phenomenon was shown clearly by analysis of auto- and cross-correlation functions of firing patterns of VMN and LHA neurones. 5. The effects of stimulations of the prefrontal cortex and splanchnic afferents on VMN and LHA neurones depended on the basic firing frequency, thus they varied with the time of day. Definite relationships exist between basic firing frequency of a cell and the magnitude of changes evoked by these stimuli. Reactions of VMN and LHA neurones were the opposite in most instances. Septal stimulations (at more than 10/sec) always produced inhibition of LHA neurone activity. 6. Intravenous injection of glucose inhibited LHA neurones and accelerated firing of VMN cells. This was true during the day period as well as at night when background activities of VMN and LHA neurones were different from that of the day. 7. Stimulation of the septal area with subthreshold pulses at a low rate (1-0.3/sec) suppressed or altered oscillations in firing frequency of LHA neurones. Severance of connection between LHA and structures caudal thereto had no effect on LHA neurone firing rates or rhythms. Sections between the septal area and LHA, however, abolished or greatly altered the oscillatory rhythms of LHA cell activity, although spontaneous discharges continued at a somewhat lower rate for periods of hours. 8. Stimulation of suprachiasmatic nuclei with weak intensity and low frequency also changed oscillatory fluctuations in firing of LHA neurones. 9. Possible origins of circadian rhythm and oscillations of short duration in firing pattern of VMN and LHA neurones were discussed. (+info)
Effects of adrenomedullin and PAMP on adrenal catecholamine release in dogs.
We examined the effects of proadrenomedullin-derived peptides on the release of adrenal catecholamines in response to cholinergic stimuli in pentobarbital sodium-anesthetized dogs. Drugs were administered into the adrenal gland through the phrenicoabdominal artery. Splanchnic nerve stimulation (1, 2, and 3 Hz) and ACh injection (0.75, 1.5, and 3 microgram) produced frequency- or dose-dependent increases in adrenal catecholamine output. These responses were unaffected by infusion of adrenomedullin (1, 3, and 10 ng. kg-1. min-1) or its selective antagonist adrenomedullin-(22-52) (5, 15, and 50 ng. kg-1. min-1). Proadrenomedullin NH2-terminal 20 peptide (PAMP; 5, 15, and 50 ng. kg-1. min-1) suppressed both the splanchnic nerve stimulation- and ACh-induced increases in catecholamine output in a dose-dependent manner. PAMP also suppressed the catecholamine release responses to the nicotinic agonist 1, 1-dimethyl-4-phenylpiperazinium (0.5, 1, and 2 microgram) and to muscarine (0.5, 1, and 2 microgram), although the muscarine-induced response was relatively resistant to PAMP. These results suggest that PAMP, but not adrenomedullin, can act as an inhibitory regulator of adrenal catecholamine release in vivo. (+info)
Effects of 17beta-estradiol on the baroreflex control of sympathetic activity in conscious ovariectomized rats.
The effects of chronic treatment with 17beta-estradiol on baroreflex control of sympathetic activity were examined in conscious unrestrained ovariectomized rats. Baroreflex function was evaluated by logistic sigmoidal analysis of the relationships between changes in mean arterial pressure (MABP) and changes in heart rate (HR) and splanchnic nerve activity (SNA) when MABP was rapidly increased to 150 mmHg by intravenous phenylephrine after its reduction to 50 mmHg by intravenous nitroprusside. These baroreflex function curves were similar in vehicle- and estradiol-treated rats. However, after a 30-min infusion of vasopressin in vehicle-treated rats, the curve for HR was shifted downward, and the upper plateau and maximum gain for the SNA curve were reduced. These effects were abolished by estradiol. A 30-min phenylephrine infusion had no effect on the baroreflex curves. Thus estrogen can modulate the action of vasopressin on baroreflex control of sympathetic outflow and thereby participate in cardiovascular regulation. (+info)
Involvement of NMDA and non-NMDA receptors in transmission of spinal visceral nociception in cat.
AIM: To study the role of N-methyl-D-aspartic acid (NMDA) and non-NMDA receptors in processing nociceptive visceral information in the spinal cord. METHODS: The firing of spinal dorsal horn neurons to colorectal distension (3-15 kPa, 20 s) by inflation with air of latex balloon was recorded in 25 anesthetized cats. RESULTS: 1) According to the patterns of responses to colorectal distension, the neurons with increase and decrease in firing were classified as excitatory and inhibitory, respectively. The former consisted of 17 short-latency abrupt (SLA) neurons, 11 short-latency sustained (SLS) neurons, 9 long-latency (LL) neurons. The 15 inhibited (Inh) neurons were recorded. 2) Microelectrophoretic administration of NMDA, quisqualic acid (QA), and kainic acid (KA) activated 67.6%, 78.4%, and 59.5% of the colorectal distension-excited neurons tested. Also, 60%, 86.7%, and 53.3% of Inh neurons were activated by these 3 amino acids. 3) Colorectal distension-induced excitatory responses were reduced by 35% +/- 10% and 65% +/- 14% by a selective NMDA receptor antagonist d,l-2-amino-5-phosphonovalerate (APV) and a selective non-NMDA receptor antagonist 6,7-dinitro-quinoxaline-2,3-dione (DNQX), respectively. Such DNQX-induced inhibition was significantly more potent than that by APV (P < 0.05). Colorectal distension-induced inhibitory responses were partially relieved by 30%-50% in 3/7 Inh neurons by DNQX, but not APV. CONCLUSION: Both NMDA and non-NMDA receptors are involved in transmission and/or modulation of spinal visceral nociceptive information and non-NMDA receptors may play more important role than NMDA receptors. (+info)
Rhythmic sympathetic nerve discharges in an in vitro neonatal rat brain stem-spinal cord preparation.
To understand the origination of sympathetic nerve discharge (SND), I developed an in vitro brain stem-spinal cord preparation from neonatal rats. Ascorbic acid (3 mM) was added into the bath solution to increase the viability of preparations. At 24 degrees C, rhythmic SND (recorded from the splanchnic nerve) was consistently observed, but it became quiescent at <16 degrees C. Respiratory-related SND (rSND) was discernible and was well correlated with C(4) root activity. Power spectral analysis of SND revealed a dominant 2-Hz oscillation. In most preparations (86%), such oscillation was persistent, whereas it only slightly reduced its magnitude after isolation from the brain stem. The removal of neural structures rostral to the superior cerebellar artery (equivalent to the level of facial nuclei) reduced rSND, increased tonic SND, but did not affect the temporal coupling between SND and C(4) root activity. Our data suggest a prominent contribution of SND from the neural mechanisms confined within the neonatal rat spinal cord. This ascorbic acid-enhanced in vitro preparation is a very useful model to study neural mechanisms underlying sympathorespiratory integration. (+info)
Role of ET(B) receptors and nitric oxide in adrenal catecholamine secretion in anesthetized dogs.
We examined the effects of sarafotoxin 6c (S6c), an endothelin-B (ET(B)) receptor agonist, on adrenal catecholamine secretion in response to cholinergic stimuli in pentobarbital sodium-anesthetized dogs. Drugs were administered intra-arterially into the adrenal gland through the phrenicoabdominal artery. Infusion of S6c attenuated increases in adrenal catecholamine output induced by splanchnic nerve stimulation. The inhibitory effect of S6c on the catecholamine secretion response was suppressed with a selective ET(B) receptor antagonist N-cis 2, 6-dimethylpiperidinocarbonyl-L-gamma-methylleucyl-D-1-methoxycarbonyl tryptophanyl-D-norleucine (BQ-788), a nitric oxide synthase (NOS) inhibitor N(omega)-nitro-L-arginine methyl ester, and a neuronal NOS inhibitor 7-nitroindazole monosodium salt (7-NINA). Similar results were obtained with the catecholamine secretion response induced by injection of ACh. 7-NINA alone did not affect these catecholamine secretion responses. These results suggest that ET(B) receptors play an inhibitory role in adrenal catecholamine secretion by activating neuronal NOS, whereas neuronal NOS is unlikely to be involved in regulation of adrenal catecholamine secretion in the absence of simultaneous ET(B) receptor stimulation. (+info)
Bilateral thoracoscopic splanchnicectomy: effects on pancreatic pain and function.
OBJECTIVE: To evaluate prospectively the effect of bilateral thoracoscopic splanchnicectomy on pancreatic pain and function. SUMMARY BACKGROUND DATA: Severe pain is often the dominant symptom in pancreatic disease, despite a wide variety of methods used for symptom relief. Refinement of thoracoscopic technique has led to the introduction of thoracoscopic splanchnicectomy in the treatment of pancreatic pain. METHODS: Forty-four patients, 23 with pancreatic cancer and 21 with chronic pancreatitis, were included in the study and underwent bilateral thoracoscopic splanchnicectomy. Effects on pain (visual analogue scale) and pancreatic function (standard secretin test, basal serum glucose, plasma insulin, and C-peptide) were measured. RESULTS: Four patients (9%) required thoracotomy because of bleeding. There were no procedure-related deaths. The mean duration of follow-up was 3 months for cancer and 43 months for pancreatitis. Pain relief was evident in the first postoperative week and was sustained during follow-up, the average pain score being reduced by 50%. All patients showed a decrease in consumption of analgesics. Neither endocrine nor exocrine function was adversely affected by the procedure. CONCLUSIONS: Bilateral thoracoscopic splanchnicectomy is beneficial in the treatment of pancreatic pain and is not associated with deterioration of pancreatic function. (+info)