Orthograde axonal transport studies of projections from the zona incerta and pretectum to the basilar pontine nuclei in the rat

Abstract

This study employed orthogradely transported axonal tracers to demonstrate, in the rat, projections that reach the basilar pontine nuclei from the zona incerta or pretectal nuclei. Except for the most rostral levels, all subdivisions of the zona incerta give rise to substantive basilar pontine projections. Although some topographic differences exist among the temination patterns of various subdivisions, no clear somatotopically organized scheme is apparent. Most incertopontine axons descend to the basilar pons in association with fibers of the medial lemniscus or crus cerebri and reach ipsilateral ventral and medial pontine gray regions. A sparse number of terminals are evident in the contralateral medial pontine gray. The anterior pretectal axons also descend with the medial lemniscus and crus cerebri to enter exclusively the ipsilateral basilar pons where they terminate most densely in ventral and medial regions. Dual orthograde labeling experiments indicate that some pretectal terminal fields in the pontine gray are shared with incertopontine projections and with afferents from the dorsal column nuclei. This potential convergence of basilar pontine afferent projections is significant in light of 1) the known somatosensory input to the zona incerta and pretectum and 2), the fractured somatotopy of peripheral cutaneous inputs that arrive in the cerebellar cortex via mossy fibers. The present studies also employed electron microscopy to identify synaptic boutons formed by incerto- and pretectopontine axons, and they proved to be remarkably similar. Each is a medium to small-sized bouton that contains spheroidal synaptic vesicles and forms asymmetric membrane specializations. Most incerto- and pretectopontine boutons participate in glomerular synaptic complexes that include a single, centrally located bouton contacted on its perimeter by several types of dendritic profiles including shafts and spine-like appendages. A relatively small number of labeled boutons of either type contacts single, isolated dendritic elements in the neuropil. Taken together, these findings suggest that some basilar pontine neurons might receive convergent inputs from the zona incerta and pretectum as well as other somatosensory-related systems such as the dorsal column nuclei and sensorimotor cortex.

Amygdala Modulation of Cerebellar Learning

“…Also consistent with the foregoing anterograde tracing experiment, retrograde labeling in the CeA was exclusively ipsilateral. These data confirm a previous report (Mihailoff et al, 1989) and provide an anatomical basis for understanding the functional gating properties of CeA in auditory eyeblink conditioning.…”

“…8 A, B). The descending trajectory of BDA-labeled elements originating in the CeA were observed to be almost exclusively ipsilateral and mostly conformed to previous descriptions of the ventral amygdalofugal pathway (Hopkins, 1975;Hopkins and Holstege, 1978;Krettek and Price, 1978;Price and Amaral, 1981;Mihailoff, 1995). These caudally projecting axons were followed from the subthalamic nucleus, between the lateral aspect of the substantia nigra par compacta and red nucleus, and further through the mesencephalic reticular formation.…”

“…Axonal tract tracers were used to investigate whether the CeA could affect cerebellar learning via a direct projection to the CS pathway. (Mihailoff et al, 1989;Siegel et al, 2015). Robust anterograde labeling of axons and terminals were found in the ipsilateral BPN.…”

Three-Dimensional Topography of Corticopontine Projections from Rat Barrel Cortex: Correlations with Corticostriatal Organization

“…In the neostriatum, such local integration is also indicated by the partially overlapping projections from individual SI whisker barrels (Alloway et al, 1999). It is less clear whether pontine projections from the SI whisker barrel cortex overlap with projections from cortical regions representing other modalities (Ruigrok and Cella, 1995;Brodal and Bjaalie, 1997;Schwarz and Thier, 1999), or to what degree terminal fields from subcortical sources of pontine afferents (Kosinski et al, 1986(Kosinski et al, , 1988Aas, 1989;Aas and Brodal, 1989;Lee and Mihailoff, 1990;Mihailoff, 1995) (for review, see Ruigrok and Cella, 1995;Allen and Hopkins, 1998;Liu and Mihailoff, 1999) overlap with projections from SI.…”

Organization of the zona incerta in the macaque: An electron microscopic study

“…The ZI also has connections with the dorsal column and trigeminal nuclei (Ricardo, 1981;Roger and Cadusseau, 1985;Romanowski et al, 1985;Carstens et al, 1990), the dorsal thalamus (Ahlenius, 1978;Herkenham, 1979;Ricardo, 1981;Watanabe and Kawana, 1982;Roger and Cadusseau, 1985;Romanowski et al, 1985), the substantia nigra (Ricardo, 1981;Paré et al, 1988;Carstens et al, 1990), the mesencephalic reticular formation, including the pedunculopontine tegmental nucleus, parabrachial area, periaqueductal gray, and nucleus reticularis tegmentis pontis (NRTP) (Ricardo, 1980(Ricardo, , 1981Watanabe and Kawana, 1982;Roger and Cadusseau, 1985;Romanowski et al, 1985;Beitz, 1989;Carstens et al, 1990) the basilar pons (Mihailoff et al, 1989;Mihailoff, 1995), the perioculomotor nuclei, including the interstitial nucleus of Cajal, nucleus of Darkschewitsch, and nuclei of the posterior commissure (Ricardo, 1981), and the cerebellum (Faull and Carman, 1978;Roger and Cadusseau, 1985).…”