Mechanisms underlying the cardioinhibitory and pressor responses elicited from the medullary neurons in the gigantocellular tegmental field of cats

A stimulation of the gigantocellular tegmental field (FTG) in the medulla oblongata often increases systemic arterial blood pressure (SAP) and decreases heart rate (HR). We investigated if the cardioinhibitory/depressor areas, including the nucleus ambiguus (NA), the dorsal motor nucleus of vagus (DMV) and the caudal ventrolateral medulla (CVLM), underlied the functional expression of FTG neurons in regulating cardiovascular responses. In 73 chloralose-urethane anesthetized cats, the HR, SAP and vertebral nerve activity (VNA) were recorded. Neurons in the FTG, NA, DMV and CVLM were stimulated by microinjection of sodium glutamate (25 mM Glu, 70 nl). To study if the NA, DMV, and CVLM relayed the cardioinhibitory messages from the FTG, 24 mM kainic acid (KA, 100 nl) was used as an excitotoxic agent to lesion neurons in the NA, DMV or CVLM. We found that the cardioinhibition induced by FTG stimulation was significantly reduced by KA lesioning of the ipsilateral NA or DMV. Subsequently, a bilateral KA lesion of NA or DMV abolished the cardioinhibitory responses of FTG. Compared to the consequence of KA lesion of the DMV, only a smaller bradycardia was induced by FTG stimulation after KA lesion of the NA. The pressor response induced by Glu stimulation of the FTG was reduced by the KA lesion of the CVLM. Such an effect was dominant ipsilaterally. Our findings suggested that both NA and DMV mediated the cardioinhibitory responses of FTG. The pressor message from the FTG neurons might be partly working via a disinhibitory mechanism through the depressor neurons located in the CVLM.

The relationship between FTL and NA, DMV or CVLM in central cardiovascular control

The aim of the present study was to examine the relationship between the lateral tegmental field (FTL), a cardioinhibitory area, with other cardioinhibitory areas, i.e., the ambiguus nucleus (NA) and the dorsal motor nucleus of vagus (DMV) and the caudal ventrolateral medulla (CVLM), a vasopressor inhibitory area. In 55 cats anesthetized with chloralose (40 mg/kg) and urethane (400 mg/kg), the cardiovascular responses of heart rate (HR), systemic arterial blood pressure (SAP) and vertebral nerve activity (VNA) were recorded. The FTL, NA, DMV and CVLM were identified first by stimulation (rectangular pulses in 80 Hz, 0.5 ms, 50-100 microA) and then confirmed by microinjection of sodium glutamate (Glu, 0.25M, 70 nl). In studying the influence of NA, DMV, or CVLM lesion on the Gluinduced responses in FTL, kainic acid (KA, 24 mM, 100 nl) was microinjected into the NA, DMV or CVLM. FTL stimulation produced an average decrease of HR by 55%. After KA lesioning of the ipsilateral NA or the DMV, the decreased HR induced by FTL was significantly diminished. After subsequent lesion of the contralateral DMV or NA, the bradycardia of FTL was abolished. The reduction of resting HR was more intense after lesioning the NA than DMV and with the left side more than that of the right side. These studies suggest that the cardioinhibitory responses of FTL are mediated through both NA and DMV with predominance of the former, while the hypotensive effect of FTL is mediated through CVLM. The precise pathway responsible for the FTL-induced bradycardia and hypotension is to be determined.

Dynamic changes of touch- and laser heat-evoked field potentials of primary somatosensory cortex in awake and pentobarbital-anesthetized rats

In this investigation, changes of mechanical- (MEP) and laser-evoked potentials (LEP) in rat primary somatosensory cortex during the course of pentobarbital (PB) anesthesia were examined. Temporal analysis of changes in the magnitude and latency of MEP and LEP, EEG activity, gross motor behaviors, and the tail flick response following laser stimulation before, during, and after PB administration (50 mg/kg, i.p.) was performed and correlated in chronically implanted rats. During the wakeful condition, there were two major cortical components each following mechanical stimulation (MEP1 and MEP2, n=17) and laser stimulation (LEP1 and LEP2, n=10), respectively. After PB administration, the positive peak in MEP1 was enhanced, and all other components disappeared. These components returned with different time courses. Two hours after PB administration, when the rat had spontaneous movements and flexor reflexes, LEP2 showed reversed polarity. MEP2 returned gradually 3 h after PB administration when the rat regained its ability to execute coordinated movements. After 4 h, LEP1 began to reappear and LEP2 returned to its negative polarity. We found that PB facilitated Abeta fiber-related cortical evoked potential (MEP1), while differentially inhibited Adelta and C fiber-related components (MEP2, LEP1 and LEP2). Characterization of these anesthesia-induced changes in cortical output may be useful in studying the neural basis of tactile and pain sensations.

Frequency coding ability of the somatosensory thalamocortical system and its modulation by anesthesia depth

The purposes of the present study were to characterize and compare the mid-tail cortical and thalamic somatosensory evoked potentials (SEPs), and to examine how the depth of the barbiturate anesthesia affected them. After the tail representative locations of sacrococcygeal dorsal root (S2 or S3), thalamus (ventroposterior lateral nucleus, VPL) and primary somatosensory cortex (SI) were set up for recording, the rats were infused serially with diluted sodium pentobarbital solution beginning from light (5 to 10 mg/kg/hr) to deep (30 to 40 mg/kg/hr) and then stop infusion (recovery). The effects of anesthetic depth on SEPs were examined of dorsal root, thalamic and cortical field potentials evoked by mid-tail stimulation of various stimulation intensities (100 microA to 2mA, step 100 pA, at 2 Hz) and frequencies (0.5 to 11 Hz, step 0.5 to 1 Hz, at 3T). The depth of anesthesia did not affect the strength-response curves of the SEPs. In contrast, the depth of anesthesia differentially influenced the frequency following capabilities of different recording sites. Under light anesthesia, thalamic SEP was only significantly affected with stimulation frequencies higher than 8 Hz, whereas cortical SEP was significantly affected with 2 Hz or higher. Under deep anesthesia, thalamic SEP evoked by low frequency tail stimulation was not significantly changed. In contrast, cortical SEP was affected much strongly so that under 1 Hz stimulation, a significant difference could be observed. We concluded, therefore, that thalamus was only partially responsible for the limited frequency following capability of the SI, and that the main effect of pentobarbital was on the cortical level. From the data obtained, an exponentially decaying curve could be observed for the cortical SEP under different stimulation frequencies. The decay constant showed a 50% change with a change in anesthesia depth. We propose that the decay constant could be used as a sensitive index for the monitoring of anesthetic depth.

Cardiac and pulmonary vagal neurons receive excitatory chemoreceptor input

The effects of hypercapnia and hypocapnia on the activities of the cardiac and pulmonary vagal single fibers were examined in the decerebrated, unanesthetized, paralyzed, and vagotomized cats. The animals breathed 100% O2. Fractional end tidal CO2 concentration was raised to 9% by adding CO2 into the O2 inlet. Average discharge rate of efferent cardiac vagal units (n=10) increased from 1.0+/-0.3 to 2.2+/-0.3 Hz. Hypocapnia apnea was produced by hyperventilation. Activities of cardiac vagal units tested (n = 4) showed dramatic decrease (0.1+/-0.0 Hz). Mean arterial blood pressure did not change significantly under these conditions. In contrast, only instantaneous firing rate during inspiration was significantly increased for efferent pulmonary vagal units (n = 11) during hypercapnia. The activities of the 3 pulmonary vagal units tested with hypocapnia decreased significantly. We concluded that cardiac and pulmonary vagal neurons were excited by chemoreceptor input.

Algorithmic complexity as an index of cortical function in awake and pentobarbital-anesthetized rats

This study introduces algorithmic complexity to measure characteristics of brain functions. The EEG of the rat was recorded with implanted electrodes. The normalized complexity value was relatively independent of data length, and it showed a simpler and easier calculation characteristic than other non-linear indexes. The complexity index revealed significant differences among awake, asleep, and anesthetized states. It may be useful in tracking short-term and long-term changes in brain functions, such as anesthetized depth, drug effects, or sleep-wakefulness.

Comparison of touch- and laser heat-evoked cortical field potentials in conscious rats

Field potentials and multiunit activities from chronically implanted cortical electrodes were used to study tactile and nociceptive information processing from the tail of the rat. Fourteen stainless steel screws implanted in the skull were used as electrodes to record field potentials in different cortical areas. Electrical, mechanical, and laser pulses were applied to the tail to induce evoked cortical field potentials. Evoked responses were compared before and after sodium pentobarbital anesthesia (50 mg/kg, i.p.). In both electrical- and mechanical-evoked potential (EEP and MEP) studies, two major peaks were found in the conscious animal. The polarity of the late component was modified after pentobarbital anesthesia. In the laser-evoked potential (LEP) study, two distinct negative peaks were found. Both peaks were very sensitive to anesthesia. Following quantitative analysis, our data suggest that the first positive peak of EEP and MEP corresponded to the activation of the Abeta fiber, the second negative peak of MEP and the first peak of LEP corresponded to Adelta fiber activation, while the second peak of LEP corresponded to C fiber activation. The absolute magnitudes of all cortical components were positively related to the intensity of the stimulation. From spatial mapping analysis, a localized concentric source of field potential was observed in the primary somatosensory cortex (SI) only after activation of the Abeta fiber. Larger responsive cortical areas were found in response to Adelta and C fiber activation. In an intracortical recording experiment, both tactile and nociceptive stimulation evoked heightened unit activity changes at latencies corresponding to respective field potentials. We conclude that different cortical areas are involved in the processing of A and C fiber afferent inputs, and barbiturate anesthesia modifies their processing.

A multichannel system for recording and analysis of cortical field potentials in freely moving rats

A system has been developed to record and analyze the cortical electrical activity from 16 different sites in freely moving rats. The hardware includes a 16-channel amplifier system whose high input impedance, low noise, small size, light weight and shielded multistrand connecting cable allow high quality multichannel recording of field potentials. The software developed for this system consists of data acquisition, data analysis and topographic mapping of cortical-evoked potentials as well as electroencephalograms. Cortical field potentials evoked by CO2-laser stimulation were compared between wakeful and pentobarbital-treated conditions. To investigate the background interference produced by sleep spindle, three kinds of reference-free methods (the Wilson, local average and weighted average methods) were utilized to compare the coherence between field potentials obtained from two cerebral hemispheres using monopolar vs. reference-free recordings.

Quantitative relationship between fluctuations of blood pressure and sympathetic nerve activity in pentobarbital anesthetized rats

Transfer function analysis was used to examine the coupling between the sympathetic nerve activity (SNA) and the blood pressure (BP) fluctuations. In pentobarbital anesthetized Wistar rats, linear regression of the relationship between frequency (X-axis) and the logarithmic transfer magnitude, i.e. log (BP power density/renal SNA power density) (Y-axis), in the low frequency range (0.016-0.85 Hz) revealed an excellent fit (r = 0.97-0.98). Comparing the regression lines, rats under large dose of pentobarbital anesthesia (40 mg/kg, i.v. single dose) had significantly smaller intercept and slope values compared to rats under small dose of pentobarbital anesthesia (12.5 mg/kg). When intercept and slope values were compared between intact and acutely sinoaortic denervated rats, no significant difference were found. The results suggest that sympathetic modulation of vasomotor tone may be a major factor in generating BP fluctuations between 0.016 and 0.85 Hz in rats. Furthermore, these results support the possibility of using low frequency spectral power of BP to quantitatively estimate the fluctuations of SNA for rats under pentobarbital anesthesia if anesthetic depth is controlled.

A single minute lesion around the ventral respiratory group in medulla produces fatal apnea in cats

In 35 adult cats anesthetized with intraperitoneal chloralose and urethane, the ventrolateral medulla was explored by microinjection of kainic acid (KA, 24 mM, 200 nl) with metal electrode-tubing or glass micropipette to determine regions which elicit persistent apnea. Persistent apnea is defined as: (1) In spontaneously breathing cats, termination of respiration over 3 min with a decrease of the mean systemic arterial pressure (MSAP) to 25 mm Hg. (2) In animals under artificial ventilation and paralyzed by gallamine, cessation of bilateral phrenic nerve (PNA) activities over 25 min. The apnea producing area was located dorsal to the rostral pole of the lateral reticular nucleus, ventromedial to the ambiguous nucleus and immediately caudal to the retrofacial nucleus. Functionally, this region includes the rostral part of the ventral respiratory group (rVRG) encompassing the pre-BOtzinger area. We define this region as the VRG apnea producing area (VRG-Apa). Fatal apneusis was observed under following conditions: (1) Persistent apnea was produced after a single KA microinjection in one side of the VRG-Apa (5 animals). Microinjection of sodium glutamate (0.25 M, 70-200 nl) in the same area produced only brief apnea, while microinjection of kynurenic acid (0.1 M, 200 nl) showed little effect on the respiration but slightly increased the SAP. (2) Positioning an electrode nearby but not in the VRG-Apa with or without KA injection did not produce apnea. But when a second electrode insertion to the opposite VRG-Apa immediately produced persistent apnea even without KA injection (6 animals). (3) Midsagittal division of the medulla 0-5 mm rostral to the obex produced persistent silence of PNA on both sides in artificial ventilated animals (7 animals), while similar division 0-5 mm caudal to the obex (4 animals) produced a brief but reversible quiescence of PNA. In conclusion, findings of the present study support the existence of a restricted region of VRG-Apa. VRG-Apa on both sides are closely connected, and integrity of both VRG-Apa is essential for normal respiration.

Attenuation of cardiac but not vascular component in baroreflex of spontaneously hypertensive rats

The cardiac and vascular components of the baroreceptor reflex in spontaneously hypertensive rat (SHR) and stroke-prone spontaneously hypertensive rat (SHRSP) were compared against their counterparts in normotensive Wistar Kyoto rat (WKY). SHR, SHRSP and WKY of 12-16 weeks old were chronically instrumented for intra-arterial recording of blood pressure. Intravenous injections of phenylephrine and nitroprusside were used to challenge their baroreflex. The products of blood pressure change and the half time required for the pressure to return to the control value were used as the quantitative estimation of the blood pressure stabilizing capability. The cardiac component of the baroreflex was obtained from the change in the blood pressure stabilizing capability after blockade of beta and muscarinic receptors by atenolol and atropine, respectively. The vascular component was obtained by subtracting the cardiac component from the total stabilizing capability which was the difference after blockade with a ganglionic transmission blocker, hexamethonium. We found the cardiac component of the baroreflex of the hypertensive rats was significantly less sensitive than that of the WKY. In contrast, the vascular component of the baroreflex of the three strains did not differ significantly. Therefore, we concluded that the 12-16 week old SHRs were able to maintain a stable blood pressure due to the intact vascular component of the baroreflex.

The depressor caudal ventrolateral medulla: its correlation with the pressor dorsomedial and ventrolateral medulla and the depressor paramedian reticular nucleus

The functional correlation of the depressor caudal ventrolateral medulla (CVLM) with the two pressor regions, i.e. rostral ventrolateral medulla (RVLM) and dorsomedial medulla (DM), and with another inhibitory region, i.e. the paramedian reticular nucleus (PRN), were studied in cats anesthetized intraperitoneally with chloralose (40 mg/kg) and urethane (400 mg/kg). Systemic arterial pressure (SAP), heart rate (HR) and the sympathetic vertebral nerve activity (VNA) were recorded. The correct location of CVLM, RVLM or DM was determined by their specific responses, i.e. decreases of SAP, HR and VNA, for CVLM increases of these parameters for RVLM and DM, elicited first by electrical stimulation (80 Hz, 0.5 ms, 50-100 microA) then followed by microinjection of glutamate (Glu, 0.25 M, 70 nl). The depressor action of PRN was produced by electrical stimulation only. It was found that the depressor responses caused by the CVLM stimulation were greatly reduced 2 h after lesioning either the RVLM or DM by microinjection of kainic acid (KA, 24 mM, 200 nl) ipsilateral to the side of CVLM stimulation. The CVLM responses were further reduced after the remaining side of RVLM or DM was lesioned. The reduction of the CVLM-depressor responses was more apparent after the RVLM than DM lesioning. Data suggest that the CVLM-depressor responses are mediated through inhibition of the sympathetic-pressor neurons in both RVLM and DM with predominance of the former. Lesioning the PRN by KA and/or combination with DC electrolytic lesion reduced the CVLM-induced depressor responses. In turn, lesioning the CVLM by KA reduced the PRN-induced depressor responses. The reduction in the later manipulation was more apparent in the PRN-depressor responses than the CVLM-depressor responses. Data suggest that part of the PRN depressor action is mediated through activation of the CVLM.

Vagal innervation of the gastrointestinal tract arises from dorsal motor nucleus while that of the heart largely from nucleus ambiguus in the cat

The origin of medullary cells that form the cardiac vagal branch and the vagal branches in the lower thorax innervating the gastrointestinal (GI) tract was studied using horseradish peroxidase (HRP), a retrograde transport tracer in the cat. The distributions of parasympathetic postganglionic neurons of the heart were studied with acetylcholinesterase histochemistry. Intracardiac ganglionic neurons were found mainly in the connective tissue surrounding the base of the pulmonary arteries and in an area in and dorsal to the interatrial septum. Following injection of HRP into the subepicardum where most of the cardiac postganglionic neurons reside, 91% of the labelled neurons were found bilaterally distributed in the nucleus ambiguus (NA). A small population of labelled neurons was found in the dorsal motor nucleus of the vagus (DMV) and an intermediate zone (IZ) between the two nuclei. When HRP was injected into the left or right cardiopulmonary vagus branch, labelled neurons were found exclusively in the ipsilateral NA, DMV and IZ with a predominance in the NA. In the thorax, after they course around the heart, the left and right thoracic vagus nerves divides into a left and a right branch, respectively. The left branch of the left thoracic vagus joins the left branch of the right thoracic vagus to form the anterior vagus nerve at 3 cm above the diaphragm. The right branch of the right thoracic vagus nerve joins the right branch of the left thoracic vagus to form the posterior vagus nerve. After application of HRP into the right or the left branch of the left thoracic vagus, HRP labelled cells were found in the left DMV. Similarly, after application of HRP into the left or the right branch of the right thoracic vagus, labelled cells were found in the right DMV. On the other hand, when HRP was injected into the anterior vagus, labelled neurons were found bilaterally in the DMV. This suggests that all rostral branches of the thoracic vagus have their origin in the ipsilateral DMV, and intermixing occurs only at the caudal level near the diaphragm. Findings of the present experiments suggest that parasympathetic preganglionic neurons innervating the GI tract are located exclusively in the DMV while those of the heart are located mainly in the NA. Within the DMV, GI vagal neurons were found medially from the level 0-2.5 mm rostral to the obex. In contrast, cardiac vagal neurons were found in the lateral edge of the DMV at the level 0-1 mm rostral to the obex.

A simple method for the construction of a recording-injection microelectrode with glass-insulated microwire

A rapid method for the production of a glass-insulated microwire electrode is described. A microwire was threaded into a glass capillary which was then pulled on a vertical pipette puller. A conical tip of the microwire was formed when the strongly heated glass capillary broke together with the wire in it. A tight seal of the glass-insulated microwire electrode between the glass and the metal was accomplished with silicone glue. The manufactured electrode performed consistently at different immersion depths, and yielded stable recordings of single units in the cerebral cortex and the medulla of rats. The strength and low impedance characteristics of the glass-insulated microwire electrode may make it useful for the recording of single units in deep brain structures. Furthermore, the electrode can be easily combined with another glass micropipette to form a dual recording-injection microelectrode unit.

Frequency dependent sympathetic modulation of vasomotor tone in the anesthetized rat

The hypothesis that sympathetic nerve system modulates a specific frequency range of blood pressure fluctuation was tested by electrical stimulation of the medullary sympathetic excitatory sites in anesthetized, paralyzed, vagotomized, cardiac sympathetic blocked, baroreceptor transected and angiotensin II converting enzyme inhibited rats. The frequency tested ranged from 0.02 to 1.7 Hz. For blood pressure fluctuation within this range there was no specific sympathetic reactive zone. Instead, low frequency fluctuation of sympathetic flow produced blood pressure fluctuation of the same frequency. Transfer magnitude of renal sympathetic activity to blood pressure decrease logarithmically with the increase of stimulation frequency. The relationship between the sympathetic spectral power (P(SND), (microV.s)2/Hz) and the blood pressure spectral power (P(BP), mmHg2/Hz) was found as P(BP)=10(1.3) x P(SND) x 10(-4.7x(frequency)). This transfer function demonstrates that when blood pressure fluctuation is used to estimate the sympathetic activity, it should be frequency weighted.

[A survey on sex knowledge and medical demand of the cases in Kaohsiung city adolescent health clinic]

The purpose of this survey is to study the sex knowledge of adolescents, and to analyze their need in sex consultation and related health problem in Kaohsiung city. A total of 1,000 study subjects were recruited from May 1991 to May 1994. A self-administered questionnaire and medical records were used to obtain related information. The results were as follows: 1. The male to female ratio of study subjects was 1:2. Half of them were students, 44.1% had sexual experience, and the mean +/- standard deviation of age at first sex experience was 19.1 +/- 2.8 years. 2. The average percentage of correct knowledge was as low as 67.6%. It indicated an inadequacy of sex knowledge in adolescents. Females had better knowledge than males. Subjects who had graduated from senior high schools had better knowledge than those graduated from middle schools. No association was found between the score of sex knowledge and occupation. 3. 12.5% of study subjects believed that "masturbation" might cause neurasthenia, kidney malfunction and loss of memory, while 11.9% recognized that "nocturnal emission" might result in abnormal ejaculation, mental aberration and guilty feelings. Furthermore, 3.8% considered that kissing, hugging or sleeping together might cause pregnancy. 4. Most adolescents felt that "guidance on sex knowledge" was the major reason for them to visit the adolescent clinic and "obstetric and gynecological problems" was the second most important. 5. Males and females have the same prevalence of sex experience, and 50.6% of them did not practice contraception. 88.9% subjects had a high risk of getting pregnancy. 6. Males had a higher percentage of more than one heterosexual partner than females did. There was a higher percentage of people with a high education level having a fixed heterosexual partner than that of those with a low education level.

Purification and characterization of a novel 70-kDa brain protein associated with seizure activities

Using ion exchange HPLC and ammonium sulfate precipitation, we have purified a 70-kDa protein (P70) specific to the cobalt-induced epileptogenic cortex of rat cerebrum and determined certain of its biochemical properties. P70 has a similar isoelectric point (pI; 4.6-4.8), amino acid composition and N-terminal amino acid sequence to rat serum albumin (RSA). Intracortical application of purified P70 to the motor area of normal rat cerebrum induces both ECoG seizure discharges and behavioral seizures. The data suggest that P70 is a novel albumin-like protein linked to the generation of seizure activities. However, it can be clearly distinguished from RSA, since it is able to produce seizure, is a glycoprotein and can be readily separated from RSA by 2-dimensional electrophoresis.

Enhanced sympathetic reactivity to glutamate stimulation in medulla oblongata of spontaneously hypertensive rats

The distribution and reactivity of vasomotor sites in the ventrolateral (VLM) and dorsomedial medulla (DMM) of stroke-prone spontaneously hypertensive rats (SHRSP), spontaneously hypertensive rats (SHR), and Wistar-Kyoto rats (WKY) were compared. Rats were anesthetized with alpha-chloralose and urethan. Baroreceptor denervation and vagotomy were performed. L-Glutamate (Glu, 10 mM, 30 nl) was microinjected into the DMM or VLM to identify vasoactive sites. The extent and the patterns of distribution of these sites in the three strains of rats were similar. The dose-response curve of the vasoactive site was studied with 1-500 pmol of Glu. The maximum responses of blood pressure and renal sympathetic activity were larger and threshold doses of Glu were lower in hypertensive rats. The significance of the differences among the strains was analyzed before and after adjustment for baseline pressure or activity. Most of the differences were statistically significant before baseline adjustment. After baseline adjustment, many differences between the SHRSP and the WKY remained significant. However, the only significant difference detected between the SHR and the WKY was the threshold dose for eliciting renal sympathetic change in the caudal VLM. These results suggest that there may be a general increase in excitability of the vasomotor neurons in the medulla of the hypertensive rats.

Effect of conduction distance on amplitude and area of compound action potentials of A fiber and C fiber

We used 24 sacral dorsal roots of the rat to analyze amplitude and area changes of biphasic and monophasic compound action potentials (CAPs) at 4 conduction distances. Both the CAPs of the A-fiber and C-fiber were analyzed. The changes were examined with the paired t test and linear regression. All the variables decreased linearly with increasing conduction distance except area of monophasic CAP, which remained constant throughout. CAP data were also compared between the S1 and S2 roots by using the pooled t test. Only area of monophasic CAP showed good correspondence with the anatomical data. Therefore, area of monophasic CAP is suggested as the best parameter for representing the functional state of a nerve.

Study of the hemodynamic contributing factors of spontaneously hypertensive rats in the early stage of established hypertension

The neural and nonneural factors contributing to maintain the hemodynamic status in 14 to 16 weeks old stroke prone spontaneously hypertensive rats (SHRSP) and spontaneously hypertensive rats (SHR) were compared with those of the age matched normotensive Wistar Kyoto (WKY) rats under chloralose-urethane anesthesia. The ascending aortic blood flow, arterial blood pressure and heart rate were measured under resting condition, ganglionic blockade by hexamethonium, 5 mg/kg i.v. and maximum vasodilation by hexamethonium and 0.07 mg/kg nitroprusside. The neural component (hexamethonium blockable component) was the major factor in the maintenance of resting blood pressure and total peripheral resistance index (TPRI) in the above three strains of rats. In contrast, the residual component after hexamethonium and nitroprusside administrations was the most important controlling factor for cardiac index (CI). In SHRSPs, the neural component of TPRI and residual component of CI were both significantly higher than those of WKYs by 75% and 47%, respectively. In SHRs, the residual component of CI was 52% higher than that of WKYs. These results suggest that both the increased neural component of TPRI and nonneural component of CI are important contributing factors for the blood pressure increase in the early stage of established hypertension in SHRSPs. On the other hand, in the age matched SHRs, the most important contributing factor for hypertension is the increased nonneural component of CI. Considering the differences between these two strains of hypertensive rats, the neural component of TPRI is the major factor responsible for the different levels of hypertension in SHRSPs and SHRs.

Differential effects on sympathetic nerve activities elicited by activation of neurons in the pressor areas of dorsal and rostral ventrolateral medulla in cats

Changes of the nerve activity of the sympathetic renal and vertebral nerves were elicited by microinjection of sodium glutamate (50 nmol/100 nl) into the pressor areas of the dorsal (DM) and rostral ventrolateral medulla (RVLM) in cats under urethane-chloralose anesthesia. Animals were bilaterally vagotomized, artificially ventilated, and paralyzed with gallamine triethiodide. The vertebral nerve activity always increased when pressor responses were induced by DM or RVLM stimulation. However, the effects of medullary stimulation on the renal nerve activity were variable. Three types of renal nerve responses concomitant with the pressor responses were observed in either baroreceptor-intact or baroreceptor-denervated cats. They were: (1) augmentation (type I); (2) attenuation (type II); and (3) insignificant change (type III). Type I responses were often elicited by RVLM stimulation whereas type II responses were often elicited by DM stimulation. Findings suggested that neurons integrating these sympathetic nerve activities were not equally distributed in the pressor areas of DM and RVLM. This result supports the notion that neurons located in different pressor areas of the brainstem exert differential effects over different sympathetic nerve activities.

Coexistence of autonomic and somatic mechanisms in the pressor areas of medulla in cats

The effects of electrical stimulation and microinjection of sodium glutamate (0.5 M) in the sympathetic pressor areas of the dorsal medulla (DM), ventrolateral medulla (VLM), and parvocellular nucleus (PVC) on the knee jerk, crossed extension, and evoked potential of the L5 ventral root produced by intermittent electrical stimulation were studied in 98 adult cats anesthetized with chloralose and urethane. During electrical and glutamate stimulation of these pressor areas, in addition to the rise of systemic arterial blood pressure marked inhibition of the spinal reflex was produced, indicating presence of neuronal perikarya responsible for these actions. Mild to moderate augmentation of spinal reflexes was also observed during brain stimulation but only in a few cases. The magnitude of the somatic effects among the pressor areas of the VLM, DM, and PVC subsequent to glutamate activation was about the same. Induced spinal reflex inhibition, independent from the baroreceptor and vagal influence, remained essentially unaltered after acute midcollicular decerebration. The inhibition was also observed in cats decerebellated 8-10 days in advance. The inhibition was not affected after bilateral electrolytic- or kainic-acid-induced lesions in the paramedian reticular nucleus (PRN). On the contrary, PRN-induced spinal reflex inhibition was attenuated after bilateral lesions in the DM or VLM. Data suggest that there coexists neuronal subpopulations in the VLM, DM, and PVC that can affect both the sympathetic pressor systems and spinal reflexes.

Presence of neuronal cell bodies in the sympathetic pressor areas of dorsal and ventrolateral medulla inhibiting phrenic nerve discharge in cats

To examine whether neuronal cell bodies (perikarya) in the pressor areas of dorsal medulla or ventrolateral medulla also modulate respiratory function, phrenic nerve activity was monitored and correlated with the pressor response in chloralose-urethane anaesthetized cats. The animals were paralyzed and artificially ventilated maintaining the end-tidal fractional concentration of CO2 at 0.04-0.05. The same pressor point in the dorsal or ventrolateral medulla was stimulated electrically (rectangular pulse of 20-200 microA, 80 Hz and 0.5 ms) and then chemically (0.25-0.5 M sodium glutamate, 80-200 nl). Areas producing pressor effects in either the dorsal or ventrolateral medulla produced a current-dependent decrease of phrenic discharge. The decrease in Pna was significant when the electrical current reached 50 microA or above. It occurred immediately before the onset of increase in blood pressure. Injection of glutamate to the same pressor point in either the dorsal or ventrolateral medulla produced a similar decrease in phrenic nerve activity. The results suggest that in the pressor areas of dorsal and ventrolateral medulla there are neuronal perikarya that can increase systemic arterial pressure and inhibit phrenic nerve activity. Whether the same or separate neurones are responsible for these responses is to be determined.

Interactive program for spectral and area analysis of compound action potentials of A-fiber and C-fiber

An interactive program was described to correct the baseline wandering of the compound action potentials (CAPs) of C-fiber, to calculate the area and the peak amplitude of CAPs, and to analyze their spectral distribution. Using this program, we found the optimal bandpass of the filter for recording CAPs to be from 10 Hz to 3 kHz.

Differential actions of the medial region of caudal medulla on autonomic nerve activities

1. The inhibitory effects produced by activation of the medial region of caudal medulla on activities of the left and right cardiac sympathetic, vagus and greater splanchnic nerves were studied in chloralose-urethane anaesthetized cats. 2. Electrical stimulation of the medial region produced an 80-92% inhibition of the sympathetic nerve activities, and a 45% and 58% inhibition of the left and right cardiac vagal nerve activities, respectively. There were no significant differences between effects elicited in the left and right autonomic nerves. Similar but smaller inhibitory effects were produced by micro-injection of sodium glutamate (0.5 mol/L) or DL-homocysteic acid (50 mmol/L) to the same medullary sites. 3. These data suggest that neurons residing in the medial medullary region exert strong inhibitory effects on autonomic nerve activities. Since the vasculature is principally innervated by sympathetic nerves, inhibition of sympathetic nerve activities might be the principal factor responsible for the depressor effects caused by activation of the medial region of caudal medulla. The heart is innervated both by sympathetic and parasympathetic nerves. Thus, their simultaneous inhibition during activation of the medial region elicits only a weak and variable inhibition of the heart.

Electrophysiological study of spinothalamic inputs to ventrolateral and adjacent thalamic nuclei of the cat

1. Extracellular and intracellular methods were used to record from fibers and neurons in the ventral lateral (VL) and adjacent nuclei of the cat thalamus. The receptive fields of the recorded units were analyzed and the units tested for inputs from the medial lemniscus (ML) and spinothalamic tract (STT) by electrical stimulation of the dorsal columns (DC) and ventrolateral funiculus (VLF) at the C2-3 spinal level. 2. Thirty-eight STT fibers were isolated in the thalamus. Their conduction velocities ranged from 15 to 75 m/s (mode 36 m/s). Adequate stimuli were found for 23 of these fibers. Seventeen were low-threshold (LT), 3 were wide-dynamic-range (WDR), and 3 were high-threshold (HT) units. 3. Five STT fibers were intra-axonally injected. Three were sufficiently well filled for analysis of their terminal fields. An intermediate-velocity STT fiber (conduction velocity 38 m/s) had a 4.3-microns axon and a single large terminal field in the central lateral nucleus (CL). The other two STT fibers were smaller, with diameters of 2.5 and 2.3 microns, conduction velocities of 15 and 19 m/s, and terminal fields made up of a few small boutons at the borders of the ventral posterior lateral nucleus (VPL). 4. Of 319 neurons isolated, 14 out of 129 (10.8%) in VL, 14 out of 76 (18.4%) in the VPL or ventral posterior medial (VPM) nucleus, 27 out of 64 (42.2%) in the CL nucleus, and 5 out of 50 (10%) in the reticular nucleus (R) responded at latencies less than 50 ms to VLF stimuli. A train of three pulses was more effective in driving VLF-responding neurons in all these nuclei than a single pulse. VLF-responding cells were widely dispersed in VL, concentrated in a focus in CL, and distributed around the borders of VPL. Most of those in VL and a small number in CL could be antidromically activated by stimulation of motor cortex. 5. Latencies of presynaptic responses (STT fibers) to VLF stimulation were short and varied from 0.8 to 3.9 ms (mode 1.6 ms). Despite this, very few fast-responding neurons were found. These were six VPL neurons (2.5 to 4 ms), one VL neuron (3 ms), and four CL neurons (3-4 ms). The initial spike latencies of the majority of thalamic neurons responding to VLF stimulation appeared in two peaks, one between 6 and 8 ms and the other at 10-15 ms.(ABSTRACT TRUNCATED AT 400 WORDS)

A modified "triangular pulse" stimulator for C-fibers stimulation

A low-cost, battery-powered stimulator is described. This device generates asymmetric current pulse with fast rising phase and slower exponential decay. The current intensity and the time constant of the exponential decay can be independently and continuously varied. An example of using this stimulator to selectively activate C-fibers is demonstrated. In this case the total charge injected in one stimulation is only 67 nanocolumb, which is much smaller than that injected by conventional DC polarization technique. Detailed information about the circuit design is described.

Inhibition of spinal reflexes by paramedian reticular nucleus

The inhibitory actions of the paramedian reticular nucleus (PRN), and its neighbouring structures, i.e., midline raphe nuclei (MRN) and dorsal medullary depressor area (DMD) on the knee jerk (KnJ) and crossed extension movement (CEM) induced by central sciatic stimulation and on the L5 ventral root response (EVRR) evoked by central tibial stimulation, were studied in cats under urethane (400 mg/kg) and alpha-chloralose (40 mg/kg) anesthesia alone, IP or further paralyzed with atracurium besylate (0.5 mg/kg/30 min), IV. Electrical stimulation of the above areas with rectangular pulses (80 Hz, 1.0 msec, 100-200 microA) decreased systemic arterial blood pressure (SAP) in an average value of: 36 +/- 3 mmHg for PRN; 19 +/- 2 mmHg for MRN; and 23 +/- 3 mmHg for DMD. The KnJ and CEM were almost completely suppressed by simultaneous PRN stimulation. The EVRR, including mono- and polysynaptic spinal reflexes with transmission velocity from 10 to 60 m/sec or above, were also suppressed. MRN stimulation only inhibited the KnJ, CEM and polysynaptic spinal reflexes with transmission velocities between 25 and 60 m/sec, but facilitated spinal reflexes with conduction velocities below 10 m/sec. On the other hand, DMD stimulation resulted in small suppression of KnJ, CEM and inhibition of polysynaptic spinal reflexes with conduction velocities between 25 and 60 m/sec. Even though MRN and DMD partially inhibited polysynaptic spinal reflexes, the magnitude of such inhibition was much smaller than that produced by PRN (-20% and -22% vs. -48%). The above-mentioned PRN effects on SAP and EVRR persisted in chronic animals decerebellated 9-12 days before.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of thalamic nociceptive neurons activated from the tail of the rat

The purpose of the present study was to map systematically in the thalamus the distribution of neurons processing nociceptive information from the tail of the rat. Pentobarbital-anesthetized and gallamine-paralyzed rats were used. Glass microelectrodes were used to record extracellularly from thalamic neurons. Noxious radiant heat stimuli were applied to the tail with a tail-flick apparatus, and the recorded neurons were localized with horseradish peroxidase deposits or by marking electrodes left in situ. A number of 121 neurons were tested of which 45 responded. Of these, 13 were located in the ventrobasal complex (VB), 17 were located in the central lateral nucleus and the parafascicular nucleus of the intralaminar nuclei (ILN). The rest of the responding neurons were located in the posterior group, the reticular thalamic nucleus, and the zona incerta. The nucleus submedius was not examined specifically. It is concluded that the VB and the ILN are two of the most important thalamic nuclei for processing nociceptive information from the tail of the rat.

Control of phrenic nerve activity and blood pressure by the medullary raphe nuclei in cats

Electrical and chemical stimulation methods were used to determine the topographic organization of the medullary raphe nuclei (MRN) in controlling the systemic arterial blood pressure (BP) and phrenic nerve activities (PNA). Decerebrated, unanesthetized and bilateral vagotomized cats were used. Effective points in the MRN were systematically explored with constant current stimulation. We found stimulation of the rostral MRN produced a decrease in PNA amplitude and increase in BP and PNA frequency. Stimulation of the caudal MRN produced increases in BP and the amplitude and frequency of PNA. Microinjection of glutamate solution into the caudal or the rostral MRN points produced qualitatively similar results. Thus, we concluded that the caudal MRN neurons had excitatory connections whereas the rostral MRN neurons had excitatory and inhibitory connections to the cardiovascular preganglionic neurons and the phrenic nerve motoneurons.

Morphology of physiologically characterized medial lemniscal axons terminating in cat ventral posterior thalamic nucleus

1. Medial lemniscal axons were identified by extra- and intracellular recording in the thalamic ventral posterior lateral nucleus (VPL) of cats and injected intracellularly with horseradish peroxidase (HRP). 2. Axons were characterized in terms of their latencies of response to stimulation of the medial lemniscus in the medulla, their receptive fields, and the temporal patterns of their discharge in response to stimulation of the receptive field with natural, hand-held stimuli. One-hundred sixty-six axons were placed in five operational groups: hair transient (Ht) (n = 41); hair sustained (Hs) (n = 45); pressure transient (Pt) (n = 14); pressure sustained (Ps) (n = 27), and deep or joint (Jt) (n = 39). 3. There was a tendency for Jt axons to have their terminations in anterodorsal parts of VPL and for those in the four cutaneous categories to have theirs in more central parts of the nucleus. 4. Nineteen injected axons with receptive fields mainly on the distal forelimb were subjected to detailed morphological analysis in terms of extent of terminal field and number of boutons. All axons ended in localized terminal fields that were more extensive anteroposteriorly than in the other dimensions. All showed an overall similarity and similar ranges of variation. There was a tendency, however, for Jt axons to have the least extensive terminations with fewest boutons. Ps axons had the most extensive terminations and largest number of boutons; Hs axons had small terminations and few boutons but Ht axons had small-to-medium arborizations with many boutons; no Pt axons were sufficiently well stained to enable comparisons of them with the others. There were no marked differences in axon diameter or conduction velocity among the five types. 5. Boutons identified light microscopically tended to be clustered in linear chains along proximal dendrites of relay neurons and electron microscopy revealed that they were terminals making synaptic contacts on relay cell dendrites and on presynaptic dendrites of interneurons. 6. These results reveal more similarities than differences among lemniscal axon terminations in VPL. Further studies of a quantitative nature on stimulus-response coupling and on the geographic distribution of lemniscal synapses on relay neurons will be required to reveal how lemniscal input is translated into relay cell output in VPL.

The morphology of physiologically identified GABAergic neurons in the somatic sensory part of the thalamic reticular nucleus in the cat

Neurons with somatic sensory receptive fields were examined electrophysiologically in the thalamic reticular nucleus of the cat. All cells had receptive fields much larger than those of neurons in the ventral posterior nucleus and were driven by less readily defined somesthetic stimuli. Response latencies to peripheral or medial lemniscal stimulation were, on average, longer than in the ventral posterior nucleus and suggested activation of the reticular nucleus cells by collaterals of thalamocortical relay cell axons arising in the ventral posterior nucleus. When injected intracellularly with horseradish peroxidase, reticular nucleus cells displayed thin axons with intrareticular collaterals and diffuse branches through much of the ventral posterior and posterior thalamic nuclei. Dendrites ended in processes resembling synaptic terminals. Electron microscopic immunocytochemistry of the same part of the reticular nucleus revealed processes immunoreactive for glutamic acid decarboxylase and identifiable as both collateral axon terminals and presynaptic dendrites of GABAergic reticular nucleus cells. These synaptically linked reticular nucleus cells and, in addition, immunoreactive somata and presynaptic dendrites received synapses from at least three varieties of nonimmunoreactive profiles.

Morphological and functional types of neurons in cat ventral posterior thalamic nucleus

Neurons in the thalamic ventral posterior (VB) nucleus of the cat were investigated by extracellular and intracellular recording and by anatomical methods involving either the retrograde transport of horseradish peroxidase (HRP) or the intracellular injection of HRP. Two morphological types of neurons could be detected by retrograde labeling from small injections of HRP in the internal capsule adjacent to VB. These two and one other type, judged to be an interneuron, could also be identified by intracellular staining. Type I cells are large, have thick proximal dendrites which branch in a tuft-like manner, and thick, rapidly conducting axons. They possess few or no dendritic appendages. Type II cells are smaller and have slender proximal dendrites which branch dichotomously and thin, slower conducting axons. Those injected intracellularly are covered in fine, hair-like dendritic appendages. Type III cells are small and have thin processes that give rise to many bulbous dilatations and no obvious axon. Type I and type II cells give off slender axon collaterals in the thalamic reticular nucleus but not in VB. Examples of both types of cell could be antidromically activated from the somatic sensory cortex. Type I and type II cells recovered histologically after intracellular recording included examples of most types of receptive field, including several forms of cutaneous and deep fields, as classified by us in a parallel intra- and extracellular study of unit responses. All but one type I cell, however, responded in a transient manner to peripheral stimulation. The remaining type I cell and all members of an admittedly small sample of type II cells responded in a sustained manner. The sample of recovered interneurons and of units that could not be driven antidromically from the cerebral cortex suggested that they, too, included all receptive field types. We conclude that submodality specificity in VB is not represented by morphological specificity in thalamocortical relay cells or interneurons. Some other functional parameter, such as tonic or phasic responsiveness, may be more obviously correlated with relay cell morphology.

DNA sequences from the adenovirus 2 genome

The sequence of 5,839 nucleotides from the adenovirus 2 genome has been determined and includes the regions between coordinates 32-44% and 66-71%. These regions contain the coding sequences for the 52,55K polypeptide, polypeptide IIIa, penton base, and the N terminus of the 100K polypeptide. Several additional unidentified open reading frames are present, including examples which overlap identified reading frames on the complementary strand and on the same strand. In conjunction with previously published sequences and those described in the accompanying papers (Akusjärvi, G., Aleström, P., Pettersson, M., Lager, M., Jöurnvall, H., and Pettersson, U. (1984) J. Biol. Chem. 259, 13976-13979; Aleström, P., Akusjärvi, G., Lager, M., Yeh-kai, L., and Pettersson, U. (1984) J. Biol. Chem. 259, 13980-13985) a complete sequence of 35,937 nucleotide pairs can now be reconstructed for the adenovirus 2 genome.

Response properties and functional organization of neurons in midline region of medullary reticular formation of cats

Extracellular single-unit recordings were made in the anesthetized cat from neurons within the medullary raphe nuclei and nearby reticular formation. The descending axons from some of these neurons were characterized in terms of length, conduction velocity, and location within the white matter of the spinal cord. The sensory properties were characterized following somatic, baroreceptor, visual, and auditory stimuli. The mean conduction velocities of the descending axons from neurons in the medullary raphe nuclei and in the magnocellular tegmental field (26 m/s) were significantly slower than the mean conduction velocities of units in the regions immediately dorsal to them (50 m/s). Action potentials in neurons in the medullary raphe nuclei and in the magnocellular tegmental field were evoked by anti-dromic stimulation from the dorsolateral portion of the spinal cord (30 of 43, 70%), whereas neurons located in more dorsal regions along the midline and in the reticular formation projected into the ventral columns (18 of 25, 72%). Neurons were most easily activated by a tap stimulus to the body surface. This stimulus activated 84% of the neurons tested. The receptive fields were large, often including the four limbs, back, and head. Tap-sensitive neurons were found throughout the regions investigated. Stimulation of hair receptors activated 37% of neurons tested, whereas 19% responded to a high-intensity cutaneous stimulus (pinch), 35% responded to baroreceptor stimuli, 32% responded to visual stimuli, and 33% responded to auditory stimuli. Neurons responsive to pinch were likely to respond to baroreceptor stimuli and unlikely to respond to visual stimuli. Neurons responsive to visual stimuli were likely to respond to auditory stimuli.

Intracellular staining of physiologically identified neurons and axons in the somatosensory thalamus of the cat

Neurons and axons responding to somesthetic stimulation in the thalamic ventrobasal complex (VB) were characterized electrophysiologically by intracellular recording and then individually injected with horseradish peroxidase. Two types of thalamocortical relay neuron were identified, primarily on the basis of dendritic morphology and axon diameter. Types with cutaneous or deep receptive fields were found in each class. Neither type had collateral axons in VB but each gave branches to the thalamic reticular nucleus (RTN). Small putative interneurons in VB and RTN neurons with somatosensory receptive fields were also injected. The RTN neurons had profusely branched widely ramifying axons in VB and adjoining nuclei. Injected medial lemniscal axons in VB had a range of receptive field properties and conduction velocities and ended in elongated anteroposterior domains with one or more dense concentrations of terminal boutons of varying size and with varying numbers of boutons.

Control of cardiovascular function by electrical stimulation within the medullary raphe region of the cat

An investigation was made of the effect on cardiovascular function of electrical stimulation within the midline medullary region of the anesthetized cat. Stimuli consisted of low-intensity trains of pulses. Stimulation sites were defined histologically and in some experiments, detailed stimulus maps were obtained for the effect of electrical stimulation on mean arterial blood pressure (MABP). In other experiments, measurements were made of changes produced by electrical stimulation on heart rate, cardiac output, cardiac contractility, and total peripheral resistance. Comparisons were made between the effect of stimulation at sites on the midline and sites to 1.5 mm more lateral. At midline sites, electrical stimulation most often produced a depression of the MABP. Effective depressor sites were located preferentially in two regions along the anteroposterior axis of the brain stem. At more lateral sites, electrical stimulation elevated the MABP. At most sites, changes in MABP occurred concomitantly with changes in total peripheral resistance while cardiac output was unchanged. Sites where electrical stimulation directly altered heart rate and cardiac contractility had a different distribution within the medulla compared with sites where stimulation changed the MABP.