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At least 73 records · Page 4Linked to original sources
PubMed1995

The dorsal midbrain anticonvulsant zone--III. Effects of efferent pathway transections on suppression of electroshock seizures and defence-like reactions produced by local injections of bicuculline.

Having provided an anatomical description of the efferent projections of the dorsal midbrain anticonvulsant zone [Shehab S. et al. (1995) Neuroscience 65, 681-695], our purpose in the present study was to establish which outputs from this region are responsible for mediating the anticonvulsant and behavioural properties of dorsal midbrain activation. The ability of unilateral injections of bicuculline into the dorsal midbrain anticonvulsant zone to suppress tonic hindlimb extension in the electroshock model of epilepsy was tested before and after three different knife cuts: (i) a transection of ipsilateral descending projections on the same side as the injection of bicuculline; (ii) an identical cut except it was placed contralateral to the injection; (iii) a cut which transected rostral projecting fibres from the dorsal midbrain anticonvulsant zone including most ipsilateral ascending and crossed descending projections. A fourth group of operated control animals was included to establish a baseline for the schedule of repeated testing. Qualitative observations of behaviour were taken immediately prior to administration of the electroshocks. Unilateral transection of ipsilateral descending efferents prevented the suppression of electroshock-induced hindlimb extension by injections of bicuculline into the dorsal midbrain anticonvulsant zone on the same side of the brain. Both the control cuts on the opposite side of the brain and the rostral cuts were ineffective. Transection of the ipsilateral descending projection on the same side as the injection of bicuculline also reduced the incidence of defensive reactions induced by the GABA antagonist, including explosive motor behaviour, oral attack and vocalization. Damage to this projection on the opposite side had little effect on the expression of behavioural reactions, neither did transection of the ascending efferents. These data suggest that ipsilateral descending efferents are critical for the suppression of electroshock-induced extension of the hindlimbs and the expression of defensive reactions elicited by activation of the dorsal midbrain.

Animals↗
PubMed1988

Calcitonin gene-related peptide containing autonomic efferent pathways to the pelvic ganglia of the rat.

Indirect immunofluorescence method was employed to investigate the involvement of calcitonin gene-related peptide (CGRP) in the autonomic efferent innervations of the pelvic visceral organs of the rat. Cells labeled with Fast blue (FB) injected into the pelvic ganglia were observed in the sacral parasympathetic nucleus; about 30% of these neurons showed CGRP-like immunoreactivity. These CGRP-like immunoreactive neurons were located in the dorsomedial part of the sacral parasympathetic nucleus, extending their dendrites mediolaterally. FB-labeled cells were also found in the upper lumbar level (L1, L2) of the spinal cord. Some of these neurons also showed CGRP-like immunoreactivity. CGRP-like immunoreactive varicose fibers were seen in the pelvic ganglia surrounding individual ganglion cells. Considerable amount of these fibers were not affected by sensory deafferentation, so they probably originated from autonomic efferent neurons.

Animals↗
PubMed1995

Involvement of cochlear efferent pathways in protective effects elicited with binaural loud sound exposure in cats.

1. Studies in guinea pigs have shown that the crossed olivocochlear efferent [crossed olivocochlear bundle (OCB)] pathways can reduce the cochlear neural desensitization caused by loud sounds. In one experimental paradigm, binaural loud sound exposure produced less damage than did monaural exposure, and various tests confirmed that this could be attributed to the OCB. In contrast, a study in cats has shown no such protection from the OCB for binaural exposures. There are some methodological differences between the cat and guinea pig studies that could account for the difference. The present study was carried out to determine whether two factors, namely anesthetic or exposure frequency, could account for the difference. Experiments were carried out in cats using barbiturate anesthesia, as in the guinea pig experiments. 2. Using a unilateral middle ear muscle (MEM) tenotomy, it was confirmed that under Nembutal anesthesia the MEM did not affect the threshold losses to monaural or binaural exposure. However, comparing results for monaural versus binaural 11-kHz exposures, there were significantly less threshold losses to the binaural exposure, independent of the presence of the MEM. No such difference between monaural and binaural exposures was seen for 3-kHz exposures. 3. By employing unilateral surgical strategies such as MEM tenotomy and/or various brain stem incisions, it was confirmed that the protection with binaural compared with monaural 11-kHz exposure was due specifically to the OCB. In unilaterally deefferented animals, binaural 11-kHz exposure always produced lower threshold losses on the OCB-intact side than on the OCB-cut side, regardless of the status of the MEM. Brain stem cuts that affected other rostrally or laterally located structures but not the OCB produced similar threshold losses bilaterally after binaural exposure, and the losses were comparable with the protected levels seen in other cases with intact OCB and binaural exposure. These data confirmed that when using an exposure frequency very similar to that used in the guinea pig experiments, a protective OCB effect could be demonstrated in cats, as previously seen in guinea pigs. The MEMs appeared to be inactive in barbiturate-anesthetized animals and were not activated by 3-, 7-, or 11-kHz exposures at 100 dB SPL for 10 min. The companion manuscript demonstrates this same effect across a wider range of exposures.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed2000

Whiskers, barrels, and cortical efferent pathways in gap crossing by rats.

Rats can readily be trained to jump a gap of around 16 cm in the dark and a considerably larger gap in the light for a food reward. In the light, they use vision to estimate the distance to be jumped. In the dark, they use their vibrissae at the farthest distances. Bilateral whisker shaving or barrel field lesions reduce the gap crossed in the dark by about 2 cm. Information from the barrel fields reaches motor areas via cortico-cortical, basal ganglia, or cerebellar pathways. The cells of origin of the ponto-cerebellar pathway are segregated in layer Vb of the barrel field. Efferent axons of Vb cells occupy a central position within the basis pedunculi and terminate on cells in the pontine nuclei. Pontine cells, in turn, project to the cerebellar cortex as mossy fibers. We trained normal rats to cross a gap in the light and in a dark alley that was illuminated with an infra-red source. When the performance was stable, we made unilateral lesions in the central region of the basis pedunculi, which interrupted connections from the barrel field to the pons while leaving cortico-cortical and basal ganglia pathways intact. Whisking was not affected on either side by the lesion, and the rats with unilateral peduncle lesions crossed gaps of the same distance as they did pre-operatively. Shaving the whiskers on the side of the face that retains its input to the pontine nuclei reduced the maximal gap jumped in the dark by the same amount as bilateral whisker shaving. Performance in the light was not affected. Regrowth of the shaved whiskers was associated with the recovery of the maximum distance crossed in the dark. In control cases, shaving the whiskers on the other side of the face did not reduce the distance jumped in the dark or in the light. These results suggest that the cerebellum must receive whisker information from the barrel fields for whisker-guided jumps.

Animals↗
PubMed1997

Sympathetic efferent pathways projecting to the bladder neck and proximal urethra in the rat.

The sympathetic innervation of the rat bladder neck and proximal urethra (BN/PU) was investigated by measuring BN/PU pressure responses to electrical stimulation of a left lumbar splanchnic nerve (LSN) following consecutive transections of more distal nerves. L2-L6 LSN stimulation increased BN/PU pressure. BN/PU pressure responses did not change after section of the right hypogastric nerve (HGN) but significantly decreased after subsequent sectioning of the commissural branches (CB-MPG) between the right and left major pelvic ganglia (MPG) (22%) and the commissural branches (CB-APG) between right and left accessory pelvic ganglia (APG) (30%). In other animals BN/PU pressure responses were slightly decreased (< 11%) after sectioning the left HGN and then significantly decreased by subsequent sectioning of the CB-MPG (< 21%) and CB-APG (< 36%). BN/PU pressure responses were decreased by sectioning the branches from the MPG to the APG (25%) or postganglionic nerves (MPG-PN) from the MPG to the BN/PU (37%). When the HGN on one side and all branches from the MPG on the contralateral side except for the CB-MPG were transected, increases in BN/PU intraluminal pressure were still elicited by LSN stimulation but were eliminated by transection of the CB-MPG. These results indicate that the left lumbar sympathetic pathway to the BN/PU passes through multiple crossing points at the level of the inferior mesenteric ganglion, MPG and APG and that this pathway could maintain closure of the internal urethral sphincter following various unilateral neural injuries.

Animals↗