Topographic organization ot spinal ana trigeminal somatosensory pathways to the rat parabrachial and Kölliker—fuse nuclei

Abstract

We examined the organization of somatosensory projections to the parabrachial (PB) and Kölliker-Fuse (KF) nuclei by employing the retrograde and anterograde axonal transport of Fluorogold and Phaseolus vulgaris-leucoagglutinin (PHA-L), respectively. Small PHA-L injections were made into different parts of the spinal trigeminal complex, including the paratrigeminal nucleus, and into different segments and laminae of the spinal dorsal horn. The subnuclear distribution of axonal labeling in the PB and KF was mapped with a camera lucida. Our results show that the somatosensory input to the PB and KF is highly organized. Neurons in the spinal trigeminal nuclei project predominantly to the KF and to the ventral portion of the external lateral PB. Neurons in the paratrigeminal nucleus project to the ventral lateral PB, the external medial PB, and to caudal aspects of the medial PB. These findings were supported by retrograde tracing experiments with Fluorogold. Spinal cord neurons located in the superficial dorsal horn (laminae I-II) of upper cervical segments project specifically to the ventral portion of the external lateral PB and, although more sparsely, to various other lateral PB nuclei. In contrast, neurons in the superficial dorsal horn of thoracic and lumbar spinal segments project mainly to the dorsal lateral and the central lateral PB. Finally, neurons in the lateral reticulated area and the lateral spinal nucleus of all spinal segments project almost exclusively to the internal lateral PB, whereas neurons in the respective nuclei of upper cervical segments also project to the KF. From our data we conclude that the somatosensory projections to the PB and KF are topographically organized. It is assumed that these pathways, which run from trigeminal and spinal neurons through the PB and KF to various forebrain, medullary, and spinal nuclei, form functionally different neural circuits that are involved in somatoautonomic processing.

Transneuronal Labeling of a Nociceptive Pathway, the Spino-(Trigemino-)Parabrachio-Amygdaloid, in the Rat

“…Previous anatomical studies have, however, failed to demonstrate a significant projection from the spinal dorsal horns and trigeminal nucleus caudalis (TNC) to the elPB (Blomqvist et al, 1989). Rather, afferents from nociceptive regions of the dorsal horn, laminae I and V, terminate in nuclei located in the lateral parabrachial area surrounding the elPB, none of which project to the amygdala (Bernard et al, 1995;Feil and Herbert, 1995;Saper, 1995).…”

“…The extensive dendritic labeling of elPB neurons after Fluoro-gold injections provides clues to how the connection is made. The dendrites of elPB neurons retrogradely labeled from the Ce extended into spinal lamina I terminal areas in the lateral parabrachial complex (Bernard et al, 1995;Feil and Herbert, 1995). Ultrastructural analysis has, in fact, demonstrated synaptic contacts between spinal afferents and the dendrites of amygdala- projecting neurons in the lateral parabrachial area (Ma and Peschanski, 1988).…”

“…Previous anatomical studies have, however, failed to demonstrate a significant projection from the spinal dorsal horns and trigeminal nucleus caudalis (TNC) to the elPB (Blomqvist et al, 1989). Rather, afferents from nociceptive regions of the dorsal horn, laminae I and V, terminate in nuclei located in the lateral parabrachial area surrounding the elPB, none of which project to the amygdala (Bernard et al, 1995;Feil and Herbert, 1995;Saper, 1995).To explain this discrepancy, it has been proposed that elPB neurons might have long dendrites that extend into the external nuclear layer where spinal and trigeminal afferents terminate (Blomqvist et al, 1989;Saper, 1995). There is ultrastructural evidence that spinal and trigeminal afferents contact amygdala projection neurons in the lateral parabrachial area (Ma and Peschanski, 1988), but in this study, neither the laminae of origin of the spinal and trigeminal neurons nor the subnuclear location of these synapses within the lateral parabrachial complex was determined.…”

Respiratory Rhythm Entrainment by Somatic Afferent Stimulation

“…However, our data also suggests a potential role for spinal somatosensory pathways in activating the inspiratory on-switching neurons in this region. Support for this comes from the direct projection of dorsal horn neurons to the ipsilateral dorsolateral parabrachial nucleus (Cechetto et al, 1985;Bernard et al, 1995;Feil and Herbert, 1995).…”

NMDA and GABAAreceptors in the rat Kölliker‐Fuse area control cardiorespiratory responses evoked by trigeminal ethmoidal nerve stimulation

“…Herbert et al 1990) and from spinal and trigeminal neurons which are the primary relays for sensory afferent information from the upper airways and the face (Panneton et al 1994;Feil & Herbert, 1995). In the present study, we focus on the role of the KF in mediating the nasotrigeminal reflex.…”