Biomedical subjects

Caroline Dufresne

Publications and source records attributed to Caroline Dufresne.

4 recordsLinked to original sources

PubMed2005

Cholinergic modulation of vibrissal receptive fields in trigeminal nuclei.

In sensory systems, it is usually considered that mesopontine cholinergic neurons exert their modulatory action in the thalamus by enhancing the relay of sensory messages during states of neural network desynchronization. Here, we report a projection heretofore unknown of these cholinergic cells to the interpolar division of the brainstem trigeminal complex in rats. After FluoroGold injection in the interpolar nucleus, a number of retrogradely labeled cells were found bilaterally in the pedunculopontine tegmental nucleus, and immunostaining revealed that the vast majority of these cells were also positive for choline acetyltransferase. Immunostaining for the acetylcholine vesicular transporter confirmed the presence of cholinergic terminals in the interpolar nucleus, where electron microscopy showed that they make symmetric and asymmetric synaptic contacts with dendrites and axon terminals. In agreement with these anatomical data, recordings in slices showed that the cholinergic agonist carbachol depolarizes large-sized interpolaris cells and increases their excitability. Local application of carbachol in vivo enhances responses to adjacent whiskers, whereas systemic administration of the cholinergic antagonist scopolamine produces an opposite effect. Together, these results show that mesopontine cholinergic neurons exert a direct, effective control over receptive field size at the very first relay stations of the vibrissal system in rodents. As far as receptive field synthesis in the lemniscal pathway relies on intersubnuclear projections from the spinal complex, it follows that cholinergic modulation of sensory transmission in the interpolar nucleus will have a direct bearing on the type of messages that is forwarded to the thalamus and cerebral cortex.

Acetylcholine↗

PubMed2005

Feedforward inhibitory control of sensory information in higher-order thalamic nuclei.

Sensory stimuli evoke strong responses in thalamic relay cells, which ensure a faithful relay of information to the neocortex. However, relay cells of the posterior thalamic nuclear group in rodents, despite receiving significant trigeminal input, respond poorly to vibrissa deflection. Here we show that sensory transmission in this nucleus is impeded by fast feedforward inhibition mediated by GABAergic neurons of the zona incerta. Intracellular recordings of posterior group neurons revealed that the first synaptic event after whisker deflection is a prominent inhibition. Whisker-evoked EPSPs with fast rise time and longer onset latency are unveiled only after lesioning the zona incerta. Excitation survives barrel cortex lesion, demonstrating its peripheral origin. Electron microscopic data confirm that trigeminal axons make large synaptic terminals on the proximal dendrites of posterior group cells and on the somata of incertal neurons. Thus, the connectivity of the system allows an unusual situation in which inhibition precedes ascending excitation resulting in efficient shunting of the responses. The dominance of inhibition over excitation strongly suggests that the paralemniscal pathway is not designed to relay inputs triggered by passive whisker deflection. Instead, we propose that this pathway operates through disinhibition, and that the posterior group forwards to the cerebral cortex sensory information that is contingent on motor instructions.

Action Potentials↗

PubMed2005

The vibrissal system as a model of thalamic operations.

The highly segregated organization of the vibrissal system of rodents offers a unique opportunity to address key issues about thalamic operations in primary sensory and second order thalamic nuclei. In this short review, evidence showing that reticular thalamic neurons and relay cells with receptive fields on the same vibrissa form topographically closed loop connections has been summarized. Within whisker-related thalamic modules, termed barreloids, reticular axons synapse onto the cell bodies and dendrites of residing neurons as well as onto the distal dendrites of neurons that are located in adjacent barreloids. This arrangement provides a substrate for a mechanism of lateral inhibition whereby the spread of dendritic trees among surrounding barreloids determines whisker-specific patterns of lateral inhibition. The relay of sensory inputs in the posterior group, a second order nucleus associated with the vibrissal system is also examined. It is shown that in lightly anesthetized rats posterior group cells are tonically inhibited by GABAergic neurons of the ventral division of zona incerta. These observations suggest that a mechanism of disinhibition controls transmission of sensory signals in the posterior group nucleus. We further propose that disinhibition operates in a top-down manner, via motor instructions sent by cortex to brainstem and spinal cord. In this way posterior group nucleus would forward to the cerebral cortex sensory information that is contingent upon its action.

Afferent Pathways↗

PubMed2004

Vasectomy surgical techniques: a systematic review.

BACKGROUND: A wide variety of surgical techniques are used to perform vasectomy. The purpose of this systematic review was to assess if any surgical techniques to isolate or occlude the vas are associated with better outcomes in terms of occlusive and contraceptive effectiveness, and complications. METHODS: We searched MEDLINE (1966-June 2003), EMBASE (1980-June 2003), reference lists of retrieved articles, urology textbooks, and our own files looking for studies comparing two or more vasectomy surgical techniques and reporting on effectiveness and complications. From 2,058 titles or abstracts, two independent reviewers identified 224 as potentially relevant. Full reports of 219 articles were retrieved and final selection was made by the same two independent reviewers using the same criteria as for the initial selection. Discrepancies were resolved by involving a third reviewer. Data were extracted and methodological quality of selected studies was assessed by two independent reviewers. Studies were divided in broad categories (isolation, occlusion, and combined isolation and occlusion techniques) and sub-categories of specific surgical techniques performed. Qualitative analyses and syntheses were done. RESULTS: Of 31 comparative studies (37 articles), only four were randomized clinical trials, most studies were observational and retrospective. Overall methodological quality was low. From nine studies on vas isolation, there is good evidence that the no-scalpel vasectomy approach decreases the risk of surgical complications, namely hematoma/bleeding and infection, compared with incisional techniques. Five comparative studies including one high quality randomized clinical trial provided good evidence that fascial interposition (FI) increases the occlusive effectiveness of ligation and excision. Results of 11 comparative studies suggest that FI with cautery of the vas lumen provides the highest level of occlusive effectiveness, even when leaving the testicular end open. Otherwise, firm evidence to support any occlusion technique in terms of increased effectiveness or decreased risk of complications is lacking. CONCLUSIONS: Current evidence supports no-scalpel vasectomy as the safest surgical approach to isolate the vas when performing vasectomy. Adding FI increases effectiveness beyond ligation and excision alone. Occlusive effectiveness appears to be further improved by combining FI with cautery. Methodologically sound prospective controlled studies should be conducted to evaluate specific occlusion techniques further.

Humans↗