The visceral sector of the thalamic reticular nucleus in the rat

doi:10.1016/S0306-4522(01)00316-5

Neuroscience

Volume 106, Issue 4, 31 October 2001, Pages 745-755

https://doi.org/10.1016/S0306-4522(01)00316-5 Get rights and content

Abstract

Visceral sensory perception is subjected to modulation by attention or distraction, like other sensory systems. The thalamic reticular nucleus is a key region in selective attention, effecting a change in the mode of thalamocortical transmission. Each major thalamocortical system is connected with a particular sector of the thalamic reticular nucleus. No connections from the thalamic reticular nucleus have been described to the visceral sensory thalamus. We used axonal tracing techniques to study the possible existence of reciprocal connections between the visceral sensory relay in the lateral ventroposterior parvicellular thalamic nucleus, and the reticular nucleus of the thalamus. We also studied the projections from the visceral sensory cortex, located in the granular insular cortex in the rat, to the reticular nucleus of the thalamus. We found a convergent input from both thalamic and cortical sensory visceral regions to the same sector of the reticular nucleus of the thalamus. This visceral sector in turn sent GABAergic feedback connections to the lateral ventroposterior parvicellular thalamic nucleus. In addition, the visceral thalamus received histaminergic projections from the tuberomammillary nucleus, and noradrenergic projections from the locus coeruleus; both nuclei belong to the ascending activating system.

Our findings indicate that the visceral sensory thalamocortical pathway is connected to the same subcortical structures that provide attention mechanisms for other thalamocortical systems.

Section snippets

Experimental procedures

Sprague–Dawley rats were anesthetized with a mixture of ketamine/xylazine (50/10 mg/kg) i.p. and placed on a stereotaxic apparatus. Under aseptic conditions, they received micropipette pressure injections (3 nl each) aimed at the ventroposterior parvicellular thalamic nucleus (VPpc); the coordinates (Paxinos and Watson, 1986) were: 3.8 mm caudal to bregma, 2.2 mm lateral, and 6.8 mm depth. Another group of rats received tracer injections (3 nl) in the insular cortex, under direct visual

Injection sites

The VPLpc is a small thalamic nucleus that is difficult to define based only on cytoarchitectonics. Moreover, the VPLpc connects to cortical and subcortical areas that are adjacent to gustatory areas related to the VPMpc, which lies just medial to the VPLpc. For these reasons, we used several approaches to make a precise delimitation of the injection sites. We first used Nissl stain to map the spatial relationships of the VPLpc with more clearly defined thalamic structures, like the ventral

Injection sites

The small size of VPLpc made it specially important to analyze in detail the location of the tracer injections. The connections from VPLpc to the insular cortex (Cechetto and Saper, 1987, Allen et al., 1991) proved crucial to assess the placing of the thalamic injections, and to confirm the location of the visceral (as opposed to the gustatory) sector of TRN. We found that only injections that involved VPLpc produced strong anterograde axonal labeling in layer 4 of the granular insular cortex,

Conclusion

We demonstrated the existence of a visceral sensory sector in the TRN, which receives projections from the visceral sensory thalamic nucleus (VPLpc), and from the visceral sensory cortex. The visceral TRN sector, in turn, sends GABAergic projections back to VPLpc.

Acknowledgements

This research was supported by the Lineas Complementarias FONDECYT Grant 8980006. We thank Dr. J. Olavarrı́a for helpful comments on the manuscript, and Margarita Meynard and Paloma González for technical help.

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The visceral sector of the thalamic reticular nucleus in the rat

Abstract

Section snippets

Experimental procedures

Injection sites

Injection sites

Conclusion

Acknowledgements

Gastroenterology

Neurosci. Lett.

Trends Neurosci.

Neurosci. Res.

Brain Res.

Brain Res.

Neuroscience

Electroencephalogr. Clin. Neurophysiol.

Brain Res.

Nucleus gracilis: an integrator for visceral and somatic integration

J. Neurophysiol.

Organization of visceral and limbic connections in the insular cortex of the rat

J. Comp. Neurol.

The parabrachial area: electrophysiological evidence for an involvement in visceral nociceptive processes

J. Neurophysiol.

Responses of neurons in and near the thalamic ventrobasal complex of the rat to stimulation of uterus, cervix, vagina, colon, and skin

J. Neurophysiol.

Evidence for a viscerotopic sensory representation in the cortex and thalamus in the rat

J. Comp. Neurol.

Glutamate inhibits thalamic reticular neurons

J. Neurosci.

A new intrathalamic pathway linking modality-related nuclei in the dorsal thalamus

Nature Neurosci.

The function of the reticular thalamic complex: The searchlight hypothesis

Proc. Natl. Acad. Sci. USA