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PubMed1990

Morphological plasticity in efferent pathways to the urinary bladder of the rat following urethral obstruction.

Partial urethral ligation in female Wistar rats produces changes in the neural control of the lower urinary tract including bladder hyperactivity and facilitation of a spinal micturition reflex pathway. To gain insight into the mechanisms underlying these changes, axonal tracing studies were conducted to examine the postganglionic efferent limb of the micturition reflex pathway which originates in the major pelvic ganglion (MPG). Forty microliters of the tracer Fluoro-Gold (4%) were injected into the right side of the bladder in urethral-obstructed (n = 10) and control (n = 4) rats 6 weeks after urethral ligation or sham surgery. As a control Fast blue (40 microliters, 5%) was injected into the colon to label neurons in the MPG innervating the intestine. Obstructed rats exhibited a 6-fold increase (p less than 0.001) in bladder weight (0.848 gm) compared to controls (0.148 gm). A significant increase (p less than 0.001) in the size of labeled bladder postganglionic neurons in the MPG was noted in obstructed rats (576.4 microns 2, n = 4) as compared to controls (299.6 microns 2). However, labeled, colon postganglionic neurons in the MPG in obstructed (312.9 microns 2) rats were not enlarged compared to controls (359.4 microns 2). Neuronal hypertrophy was not associated with a change in the number of labeled MPG neurons in control and obstructed groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Autonomic responses and efferent pathways from the insular cortex in the rat.

The anatomical distribution of autonomic, particularly cardiovascular, responses originating in the insular cortex was examined by using systematic electrical microstimulation. The localization of these responses to cell bodies in the insular cortex was demonstrated by using microinjection of the excitatory amino acid, D,L-homocysteic acid. The efferents from the cardiovascular responsive sites were traced by iontophoretic injection of the anterograde axonal tracer Phaseoleus vulgaris leucoagglutinin (PHA-L). Two distinct patterns of cardiovascular response were elicited from the insular cortex: an increase in arterial pressure accompanied by tachycardia or a decrease in arterial pressure with bradycardia. The pressor responses were obtained by stimulation of the rostral half of the posterior insular cortex while depressor sites were located in the caudal part of the posterior insular area. Both types of site were primarily located in the dysgranular and agranular insular cortex. Gastric motility changes originated from a separate but adjacent region immediately rostral to the cardiovascular responsive sites in the anterior insular cortex. Tracing of efferents with PHA-L indicated a number of differences in connectivity between the pressor and depressor sites. Pressor sites had substantially more intense connections with other limbic regions including the infralimbic cortex, the amygdala, the bed nucleus of the stria terminalis and the medial dorsal and intralaminar nuclei of the thalamus. Alternatively, the depressor region of the insular cortex more heavily innervated sensory areas of the brain including layer I of the primary somatosensory cortex, a peripheral region of the sensory relay nuclei of the thalamus and the caudal spinal trigeminal nucleus. In addition, there were topographical differences in the projection to the lateral hypothalamic area, the primary site of autonomic outflow for these responses from the insular cortex. These differences in connectivity may provide the anatomic substrate for the specific cardiovascular responses and behaviors integrated in the insular cortex.

Animals↗
PubMed1997

Sympathetic efferent pathways projecting bilaterally to the vas deferens in the rat.

BACKGROUND: The laterality of the signals passing through the splanchnic nerves to the vas deferens has not been well studied. METHODS: The present study was designed to determine the bilateral distribution of sympathetic nerves to the rat vasa deferentia by measuring intravasal pressure (VP) responses to electrical stimulation of left lumbar splanchnic nerves (LSN) following consecutive transections of more distal nerves. RESULTS: L2-L6 LSN stimulation increased VP bilaterally. Left VP responses decreased slightly (< 20%) after section of the right hypogastric nerve (HGN) and then were abolished by subsequent section of branches (B-M-APG) between the left major pelvic (MPG) and accessory pelvic ganglia (APG). Left VP responses were decreased by > 80% after section of left HGN, not changed further by subsequent section of commissural branches (CB-MPG) between the MPG, and completely eliminated by section of commissural branches between the APG (CB-APG). Right VP responses were decreased slightly (< 20%) by section of the left HGN and then abolished by section of the right B-M-APG. These responses were also decreased by > 70% by section of right HGN, not changed by section of CB-MPG, but then completely eliminated by section of CB-APG. CONCLUSIONS: These results indicate that the left lumbar sympathetic pathway to the vas deferens is distributed bilaterally and exhibits two crossing points at the level of the inferior mesenteric ganglion and APG.

Adrenergic Fibers↗
PubMed1991

Efferent pathway of the amygdala involved in conditioned fear as measured with the fear-potentiated startle paradigm.

Fear-potentiated startle in the rat is a measure of conditioned fear that is blocked by lesions of the central nucleus of the amygdala. In a companion study, Rosen, Hitchcock, Sananes, Miserendino, and Davis (1991) demonstrated a direct anatomical projection from the central nucleus to the brainstem startle reflex circuit. In the present study, fear-potentiated startle was blocked by lesions that interrupted this pathway at 3 different levels or by a crossed lesion that interrupted the pathway at its source on one side and at a more caudal level on the other side. Although synaptic relays have not been ruled out entirely, the data suggest that the direct projection from the central nucleus of the amygdala to the startle circuit mediates the expression of fear-potentiated startle. These findings are consistent with the literature indicating that efferent projections from the central nucleus to various brainstem structures are involved in the expression of several conditioned fear responses.

Amygdala↗
PubMed1989

Organization of afferent and efferent pathways in the pudendal nerve of the female cat.

Application of horseradish peroxidase to the pudendal nerve in the female cat labelled lumbosacral afferent and efferent neurons and their processes. Afferent axons entered the spinal cord primarily at the S1 and S2 segments and traveled rostrocaudally in Lissauer's tract and the dorsal columns. A distinctive component of the dorsal column projection was located at the lamina I-dorsal column border as a densely labelled, compact bundle that distributed fibers to the dorsal horn at spinal levels near the segments of entry of the afferent axons. Afferent terminal labelling was located in the marginal zone, the intermediate gray matter, and the dorsal gray commissure in the lumbosacral and coccygeal spinal cord. A well-defined terminal field restricted to the S1 and rostral S2 segments was present in the medial third of the nucleus proprius and substantia gelatinosa. Labelled motoneurons in Onuf's nucleus (S1 and S2) exhibited longitudinal dendrites that extended rostrocaudally within the nucleus and three groups of transverse dendrites that emanated periodically from the nucleus and passed to the ventrolateral funiculus, the intermediate gray, and the dorsal gray commissure. Components of the pudendal nerve that innervate the anal and urethral sphincters were also labelled by injecting HRP into the respective sphincter muscles. Motoneurons innervating the anal and urethral sphincters were located in the dorsomedial and ventrolateral divisions, respectively, of Onuf's nucleus. Afferent projections from the two sphincters were similar; the most prominent terminations were present in the marginal zone, intermediate gray, and dorsal gray commissure. These results are discussed with respect to the physiological function of the pudendal nerve and its relationship with sacral autonomic pathways.

Afferent Pathways↗
PubMed1990

[Dorsal root potential evoked by stimulation of periaqueductal gray and its efferent pathway analysis in rats].

When periaqueductal gray (PAG) was stimulated with concentric electrodes, a steady negative potential called PAG-DRP was recorded from L5 dorsal root. PAG-DRP with properties of spatial and temporal summation propagates decrementally along the dorsal root and is inhibited by picrotoxin. Lesions of NRM had no effect on the PAG-DRP evoked by stimulation of dorsal PAG, but showed obvious reduction up to about 40% on the PAG-DRP evoked by stimulation of ventral PAG. It is suggested that the descending inhibition of PAG includes some presynaptic inhibition and that the ventral PAG-DRP is relayed partly via NRM while the dorsal PAG-DRP is not associated with NRM.

Animals↗
PubMed1998

Sympathetic efferent pathways projecting to the vas deferens.

The abdominal and pelvic sympathetic nervous system controlling the vas deferens has elaborate mechanisms to preserve its function against various injuries. The main sympathetic signals to the vas deferens proceed the common pathway in mammalians, which consists of the lumbar splanchnic nerve, caudal mesenteric plexus, hypogastric nerve, pelvic plexus and its branches. On the way of this common pathway, some signals cross to the other side of the body at the level of the caudal mesenteric plexus and/or the pelvic plexus. The preganglionic axons passing through the hypogastric nerve very likely provide a bilateral innervation to postganglionic neurons in the pelvic plexuses, which also exhibit crossing to the bilateral vasa deferentia. The sympathetic nerves originating from the thoracic spinal cord are of minor importance in contraction of the vas deferens but possibly influence it by the hormonal system consisting of the major splanchnic nerve and the adrenal medulla. When the common pathway is interrupted, various compensatory mechanisms are generated: enhancement of the remaining sympathetic pathways or reorganization of synaptic connection in the pelvic plexus. Surgical reconstruction of the transected hypogastric nerve is possible and cross-innervation mechanism via the hypogastric nerve can also be preserved. Elevation of intraluminal pressure at the cauda epididymis/proximal vas deferens induced by nerve impulse pushes the spermatozoa out to the ampulla and distention of the wall of the ampulla triggers its contraction to emit the content into the urethra. After seminal emission, a portion of the seminal fluid remaining in the vas deferens moves in a retrograde direction to the cauda epididymis for the next emission. It remains to be seen whether similar mechanisms in animals are at work in humans.

Adrenal Medulla↗
PubMedDate not supplied

Projections from V1 to lateral suprasylvian cortex: an efferent pathway in the cat's visual cortex that originates preferentially from CO blob columns.

The patchy pattern of retrograde labeling produced by injections of anatomical tracers into the lateral suprasylvian (LS) visual area was compared to the cytochrome oxidase (CO) blobs in cat visual cortex. Following large injections of anatomical tracers in LS, retrograde labeling formed an irregular lattice of patches with a spacing of slightly less than 1 mm in area 17, and slightly greater than 1 mm in area 18. By comparing labeling in alternate serial sections, patches of LS-projecting cells in both areas were found to align with CO blobs. The conclusion of alignment between CO blob columns and patches of LS-projecting cells was confirmed by a quantitative analysis which showed a significant correlation between the local density of LS-projecting cells in reconstructions of charted cells and the intensity of CO staining in the CO-reacted sections. As for areas 17 and 18, labeling in other afferent areas of LS was also patchy with a spacing on the order of 1 mm except for area 19 where we found patches of LS-projecting cells with a larger spacing, roughly 2 mm. No matching fluctuations in CO density could be discerned in area 19, however. In conjunction with recent evidence that CO blob columns in cats receive strong input from Y-cells of the lateral geniculate nucleus (Boyd & Matsubara, 1996; Shoham, et al., 1996), these data support the hypothesis (Shipp & Grant, 1991) that the patches of LS-projecting cells correspond to Y-cell input columns. As a relationship between the CO architecture and certain classes of efferent cells has previously been shown in primates, these findings show new similarities between CO blobs in different mammalian species.

Animals↗
PubMed1984

Central representation and functional connections of afferent and efferent pathways of Helix pomatia L. lip nerves.

Localization and distribution of cerebral neurones sending axons into the three pairs of Helix pomatia lip nerves were investigated by the method of retrograde axonal NiCl2 transport. Using electrophysiological technics (extracellular recordings) the dependence of lip nerve's activity on inputs of other lip nerves was studied after application of various types of stimuli to the lip of semi-intact preparations. All lip nerves have neuronal representation in each lobe of the cerebral ganglia but in different proportions. Labelled neurones were located mainly on the ventral surface of the cerebral ganglia, most of them projecting to the medial, the least to the inner lip nerve. Lip nerves differ from each other according to the proportions of neurones of various size. They share in the axons of large (55-70 microns) and medium sized (30-40 microns) neurones in the order inner greater than outer greater than medial and medial greater than outer greater than inner lip nerve, respectively. Most neurones projecting to different nerves are located in discrete groups. According to the electrophysiological results the medial lip nerve has the most prominent afferent, while the inner one has the strongest efferent activity. Both the afferent and efferent activities of the outer lip nerve proved to be the least significant compared to the other lip nerves. Contralateral cerebral connections play an important role in the sensory information processing. The sensory input of a given nerve usually activates the contralateral member of another pair of lip nerves. Mechano- and chemo-afferent pathways have almost the same properties but there are some differences in latencies and other parameters.

Afferent Pathways↗
PubMed1989

[Pressor response induced by glutamate injection into caudal ventrolateral part of periaqueductal gray matter and its efferent pathway in brain-stem].

In urethane-anesthetized, tubocurarine-immobilized artificially ventilated rats, the following results were observed: (1) Sodium glutamate (Glu) microinjection into the caudal ventrolateral part of the periaqueductal gray matter (PAG) produced a marked rise in blood pressure. (2) This effect was attenuated by phentolamine or propranolol but not by atropine, injected bilaterally into the rostral ventrolateral medulla (RVL), indicating that this pressor response is mediated by RVL and alpha- and beta-receptors. (3) Propranolol-injection into RVL also attenuated the pressor response induced by electrical stimulation of the nucleus parabrachialis ventralis (NPV), while the pressor response initiated by injecting Glu into the same area (NPV) was not affected. Taken together with the previous findings that phentolamine blocks the pressor response produced by NPV-electrostimulation, but not of Glu-injection into NPV, the above results suggest that neurons in the caudal ventrolateral part of PAG may either send axons passing through the nucleus parabrachialis (NPB) and directly acting upon beta-receptors in RVL, or relay in NPB and act indirectly on alpha-receptors in RVL to produce the pressor response.

Animals↗
PubMed2000

Sympathetic efferent pathways projecting to the prostate in the dog.

BACKGROUND: The laterality of the signals passing through the splanchnic nerves to each lobe of the prostate has not been studied. METHODS: Bilateral distribution of sympathetic signal to both lobes of the canine prostate was determined by measuring contraction of the prostate by stimulation of thoracolumbar splanchnic nerves with or without transection of unilateral hypogastric nerve (HGN). RESULTS: The 2nd-5th lumbar splanchnic nerve (LSN) stimulation elicited prostatic contraction. Twenty-five of 27 right LSN stimulations elicited contraction of the lobe, 21 bilaterally and 4 unilaterally. Twenty-three of 25 left LSN stimulations elicited contraction of the lobe, 22 bilaterally and one unilaterally. The above stimulations did not elicit a dominant response in the lobe of the stimulated side. After transection of the right HGN, right and left LSN stimulation elicited contraction of the lobe bilaterally and did not induce dominant response in the lobe of the non-lesioned side. After transection of the left HGN, similar results were obtained. CONCLUSIONS: The results indicate that each of the LSNs sends signals to bilateral lobes via multiple routes with two crossing sites at the level of the caudal mesenteric plexus and prostate, and that the signals elicit contraction of the lobe without a dominant side.

Animals↗
PubMed1986

Efferent pathways from the region of the subfornical organ to hypothalamic paraventricular nucleus: an electrophysiological study in the rat.

Twenty-three neurons in the region of the subfornical organ (SFO) were antidromically activated by electrical stimulation of the hypothalamic paraventricular nucleus (PVN) in male rats under urethane anesthesia. Microiontophoretically (MIPh) applied angiotensin II (AII) excited the activity of all units in the region of the SFO and the effect of AII was blocked by MIPh applied saralasin (Sar), an AII antagonist, but not by atropine (Atr), a muscarinic antagonist. In these units, 12 were also excited by MIPh applied acetylcholine (ACh) while 11 were not affected and the effect of ACh was attenuated by not only MIPh applied Atr, but also Sar, suggesting that not only neurons specific for AII, but also neurons sensitive to both AII and ACh project to the PVN in the region of the SFO. Intravenously administered AII excited the activity of both types of units in the region of the SFO. Microinjected AII or ACh into the region of the SFO excited the activity of putative vasopressin (VP)-secreting units in the PVN. These results suggest that neurons projecting to the PVN in the region of the SFO may act to enhance the activity of putative VP-secreting neurons in the PVN in response to circulating AII.

Acetylcholine↗
PubMed2006

A novel pressor area at the medullo-cervical junction that is not dependent on the RVLM: efferent pathways and chemical mediators.

Chemical stimulation of a region extending from the most caudal ventrolateral medulla into the upper cervical spinal cord evoked large sympathetically mediated pressor responses. These responses were not dependent on the integrity of the rostral ventrolateral medulla (RVLM) and may be mediated by glutamatergic neurons embedded in the white matter that project to the thoracic spinal cord. We term this new region the medullo-cervical pressor area (MCPA). This region is distinct from the caudal pressor area, because blockade of the RVLM with muscimol inhibited this pressor response but not that evoked from the MCPA. This is the first study to provide functional evidence for a cardiovascular role for neurons in the cervical spinal cord white matter that innervate sympathetic preganglionic neurons (Jansen and Loewy, 1997). Using retrograde tracing, in combination with immunohistochemistry and in situ hybridization, we identified two groups of spinally projecting neurons in the region. Approximately 50% of neurons in one group were excitatory because they contained vesicular glutamate transporter 1 (VGluT1)/VGluT2 mRNA, whereas the other contained a mixed population of neurons, some of which contained either VGluT1/VGluT2 or GAD67 (glutamic acid decarboxylase 67) mRNA. Despite the fact that activation of the MCPA causes potent sympathoexcitation, it does not act to restore arterial pressure after chemical lesion of the RVLM so that a role for this novel descending sympathoexcitatory region remains to be elucidated.

Adrenergic alpha-Agonists↗
PubMed2001

Sympathetic efferent pathways projecting to the vagina in the dog.

The level of the thoracolumbar sympathetic outflow projecting to the vagina and the laterality of the signals passing through the splanchnic nerves to the vagina have not been well understood. This study was undertaken to explore the sympathetic innervation of the canine vagina by measuring intraluminal pressure of the vagina and contraction of the vaginal wall by electrical stimulation of each of the thoracolumbar splanchnic nerves with or without transection of unilateral hypogastric nerve (HGN). The 2nd-4th lumbar splanchnic nerve (LSN) stimulation elicited elevation of intraluminal pressure of the vagina and contraction of the vaginal wall. In contrast, intermesenteric plexus stimulations caused no response in both the vaginal pressure and the wall itself. On the right side, 12 of 27 LSNs that were stimulated elicited elevation of vaginal pressure and 16 of 32 LSN stimulations caused contraction of the wall, 10 increases in tension and 6 reductions. On the left side, 14 of 26 LSN stimulations elicited elevation of vaginal pressure and 12 of 27 LSN stimulations caused contraction of the wall, 5 increases in tension and 7 reductions. After transection of the right HGN, 6 of 14 right LSN stimulations elicited elevation of vaginal pressure and 10 of 15 right LSN stimulations caused contraction of the wall, 9 increases in tension and 1 reduction. After transection of the left HGN, 13 of 19 left LSN stimulations elicited elevation of vaginal pressure and 10 of 18 left LSN stimulations caused contraction of the wall. 4 increases in tension and 6 reductions. The results indicate that each of the L2-L4 LSNs on either side sends signals to the canine vagina via multiple routes with a crossing site at the level of the caudal mesenteric plexus (CMP).

Animals↗
PubMed2001

Locomotor activity induced by the non-competitive N-methyl-D-aspartate antagonist, MK-801: role of nucleus accumbens efferent pathways.

We have recently shown that focal administration of dizocilpine hydrogen maleate (MK-801, a non-competitive N-methyl-D-aspartate antagonist) within the nucleus accumbens increases locomotor activity in a dopamine-independent manner. The purpose of this study was to investigate the neural network underlying locomotor stimulation induced by N-methyl-D-aspartate receptor blockade in the accumbens. In the first experiment, we examined the effect of different doses (1, 5 and 25 nmol) of the active and inactive enantiomers of the N-methyl-D-aspartate antagonist, (+)- and (-)-MK-801, respectively, focally administered in the nucleus accumbens. Only the active enantiomer induced a significant increase in locomotor activity; furthermore, the effect induced by the two highest doses of (+)-MK-801 was significantly different from that induced by (-)-MK-801. In the second part of the study, we performed ibotenic acid lesions to the major output nuclei of the accumbens, the ventral pallidum, mediodorsal thalamus, ventrolateral/ventromedial thalamus and pedunculopontine tegmental nucleus, to observe their effect on locomotor activity induced by focal (+)-MK-801 (25 nmol) administration into the accumbens. None of the lesions had any effect on spontaneous locomotor activity. Hyperactivity induced by accumbens MK-801 administrations was unaffected by ibotenic acid lesions of the pedunculopontine tegmental nucleus, while lesions of the mediodorsal thalamus induced only a partial inhibition. In contrast, ibotenic acid lesions of the ventral pallidum and ventrolateral/ventromedial thalamus completely blocked the motor response induced by accumbens MK-801. These data indicate that the intact mediodorsal thalamus, which has been proposed as a part of the loop that relays accumbens information to the prefrontal cortex, does not seem to be a structure of primary importance in MK-801 locomotor activity. On the contrary, the motor nuclei of the thalamus appear to play a more relevant role, suggesting that different neural substrates may mediate dopamine and glutamate functional output from the nucleus accumbens.

Animals↗
PubMed1993

Lesions of the hippocampal efferent pathway (fimbria-fornix) do not alter sensitivity of adrenocorticotropin to feedback inhibition by corticosterone in rats.

The hypothalamic-pituitary-adrenal (HPA) axis controls the diurnal and stress-induced release of adrenal corticosteroids into the general blood circulation. In turn, corticosteroids inhibit the HPA axis under basal conditions and during stress through occupation of their receptors (types I and II) in the brain by closing a negative feedback loop. The primary site in the brain at which corticosteroids act to inhibit the HPA axis has not been identified. High concentrations of both types of receptors are found in neurons of the hippocampal formation, a structure which has been reported by some, but not others, to control activity within the HPA axis by serving as a major negative feedback site. In many of these past studies, blood was collected after extensive handling or exposure to ether, conditions which do not favor the detection of basal hormone concentrations. To address these controversies, we tested the feedback sensitivity of the anterior pituitary hormone responsible for corticosteroid production, adrenocorticotropin (ACTH), to corticosterone (B), the main corticosteroid in rats, in total fornix- and, as controls, cortex-lesioned rats. All rats were given vascular catheters to avoid any handling-induced differences in plasma B or ACTH when sampling blood. In some experiments, fornix- and cortex-lesioned rats were adrenalectomized and given 1 of 3 doses of exogenous B provided in a subcutaneous pellet to ensure that plasma B was equal in different lesion groups. We hypothesized that if the hippocampal formation were an important site of B-mediated inhibition of the HPA axis, fornix-lesioned rats would have higher plasma B as a result of increased endogenous secretion in the morning or the evening compared to cortex-lesioned rats in rats with adrenal glands. In addition, we hypothesized that adrenalectomized fornix-lesioned rats given the same low to moderate levels of exogenous constant B would have higher basal and stress-induced ACTH than cortex-lesioned rats. Diurnal plasma B was not affected by fornix lesions in intact rats. Moreover, basal ACTH measured in the morning and the evening and stress-induced ACTH was the same in adrenalectomized fornix- and cortex-lesioned rats with constant exogenous B. We conclude, therefore, that information about occupancy of B receptors in the hippocampus carried by the fornix primarily subserves functions which do not directly regulate activity in the HPA axis.

Adrenalectomy↗