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The olivary pretectal nucleus is the first central connection in the pupillary light reflex pathway, the circuit that adjusts the diameter of the pupil in response to ambient light levels. This study investigated aspects of the morphology and connectivity of the olivary pretectal nucleus in macaque monkeys by use of anterograde and retrograde tracers. Within the pretectum, the vast majority of neurons projecting to the preganglionic Edinger–Westphal nucleus were found within the olivary pretectal nucleus. Most of these neurons had somata located at the periphery of the nucleus and their heavily branched dendrites extended into the core of the nucleus. Retinal terminals were concentrated within the borders of the olivary pretectal nucleus. Ultrastructural examination of these terminals showed that they had clear spherical vesicles, occasional dense-core vesicles, and made asymmetric synaptic contacts. Retrogradely labeled cells projecting to the preganglionic Edinger–Westphal nucleus displayed relatively few somatic contacts. Double labeling indicated that these neurons receive direct retinal input. The concentration of retinal terminals within the nucleus and the extensive dendritic trees of the olivary projection cells provide a substrate for very large receptive fields. In some species, pretectal commissural connections are a substrate for balancing the direct and consensual pupillary responses to produce pupils of equal size. In the macaque, there was little evidence for such a commissural projection based on either anterograde or retrograde tracing. This may be due to the fact that each macaque retina provides nearly equal density projections to the ipsilateral and contralateral olivary pretectal nucleus.

Search-and-rescue pilot Kacey Fairing returned home to Montana determined to put the past behind her and start a new life. But that won't be easy: her new partner is the man who broke her heart.

Historically, the central mesencephalic reticular formation has been regarded as a purely horizontal gaze center based on the fact that electrical stimulation of this region produces horizontal saccades, it provides monosynaptic input to medial rectus motoneurons, and cells recorded in this region often display a peak in firing when horizontal saccades are made. We tested the proposition that the central mesencephalic reticular formation is purely a horizontal gaze center by examining whether this region also supplies terminals to superior rectus and levator palpebrae superioris motoneurons, both of which fire when making vertical eye movements. The experiments were carried out using dual tracer techniques at the light and electron microscopic level in macaque monkeys. Injections of biotinylated dextran amine or Phaseolus vulgaris leukoagglutinin into the central mesencephalic reticular formation produced anterogradely labeled terminals that were in synaptic contact with superior rectus and levator palpebrae superioris motoneurons that had been retrogradely labeled. These results indicate that this region is not purely connected with horizontal gaze motoneurons. In addition, we found that the number of contacts on vertical gaze motoneurons increased with more rostral injections involving the mesencephalic reticular formation adjacent to the interstitial nucleus of Cajal. This suggests that there is a caudal to rostral gradient for horizontal to vertical saccades, respectively, represented within the midbrain reticular formation. Finally, we utilized post-embedding immunohistochemistry to show that a portion of the labeled terminals were GABAergic, indicating they likely originate from downgaze premotor neurons.

Since most gaze shifts are to targets that lie at a different distance from the viewer than the current target, gaze changes commonly require a change in the angle between the eyes. As part of this response, lens curvature must also be adjusted with respect to target distance by the ciliary muscle. It has been suggested that projections by the cerebellar fastigial and posterior interposed nuclei to the supraoculomotor area (SOA), which lies immediately dorsal to the oculomotor nucleus and contains near response neurons, support this behavior. However, the SOA also contains motoneurons that supply multiply innervated muscle fibers (MIFs) and the dendrites of levator palpebrae superioris motoneurons. To better determine the targets of the fastigial nucleus in the SOA, we placed an anterograde tracer into this cerebellar nucleus in Macaca fascicularis monkeys and a retrograde tracer into their contralateral medial rectus, superior rectus, and levator palpebrae muscles. We only observed close associations between anterogradely labeled boutons and the dendrites of medial rectus MIF and levator palpebrae motoneurons. However, relatively few of these associations were present, suggesting these are not the main cerebellar targets. In contrast, labeled boutons in SOA, and in the adjacent central mesencephalic reticular formation (cMRF), densely innervated a subpopulation of neurons. Based on their location, these cells may represent premotor near response neurons that supply medial rectus and preganglionic Edinger–Westphal motoneurons. We also identified lens accommodation-related cerebellar afferent neurons via retrograde trans-synaptic transport of the N2c rabies virus from the ciliary muscle. They were found bilaterally in the fastigial and posterior interposed nuclei, in a distribution which mirrored that of neurons retrogradely labeled from the SOA and cMRF. Our results suggest these cerebellar neurons coordinate elements of the near response during symmetric vergence and disjunctive saccades by targeting cMRF and SOA premotor neurons.

A projection by the superior colliculus to the supraoculomotor area (SOA) located dorsal to the oculomotor complex was first described in 1978. This projection’s targets have yet to be identified, although the initial study suggested that vertical gaze motoneuron dendrites might receive this input. Defining the tectal targets is complicated by the fact the SOA contains a number of different cell populations. In the present study, we used anterograde tracers to characterize collicular axonal arbors and retrograde tracers to label prospective SOA target populations in macaque monkeys. Close associations were not found with either superior or medial rectus motoneurons whose axons supply singly innervated muscle fibers. S-group motoneurons, which supply superior rectus multiply innervated muscle fibers, appeared to receive a very minor input, but C-group motoneurons, which supply medial rectus multiply innervated muscle fibers, received no input. A number of labeled boutons were observed in close association with SOA neurons projecting to the spinal cord, or the reticular formation in the pons and medulla. These descending output neurons are presumed to be peptidergic cells within the centrally projecting Edinger–Westphal population. It is possible the collicular input provides a signaling function for neurons in this population that serve roles in either stress responses, or in eating and drinking behavior. Finally, a number of close associations were observed between tectal terminals and levator palpebrae superioris motoneurons, suggesting the possibility that the superior colliculus provides a modest direct input for raising the eyelids during upward saccades.

Research indicates that access to higher education is insufficient: a focus on student attainment through and beyond postsecondary education is needed (Carrell & Sacerdote, 2017). This study assesses the impact of a college attainment program serving underrepresented female students. Mixed-methods combined quantitative measures of student outcomes with qualitative analysis of perceptions regarding program impact. Qualitative indicators were compared with the literature on key characteristics of college attainment programs (Webb et al, 2017). Findings indicate academic and social gains for participants and highlight associated program strategies. Results will inform the development, implementation, and evaluation of college attainment programs supporting all students.

The ventral posterior medial nucleus (VPM) is amandatory relay for orofacial sensory information targeting the primary somatosensory cortex. We characterized the morphology of VPM axons arising in the principal trigeminal sensory nucleus (pV) through injections of biotinylated dextran amine (BDA) placed in pV of and monkeys. Labeled terminals formed a patchy bilateral distribution. Within contralateral VPM, patches were found primarily, but not exclusively, within the laterally located, vertical segment, and in ipsilateral VPM, primarily, but not exclusively, in the medially located, horizontal segment. Two fiber types were labeled: thin and thick. Thin fibers were poorly branched and diffusely distributed. They were studded with small boutons. Most labeled fibers were thick and they branched extensively to form distinctive terminal arbors decorated with numerous boutons that varied in size and shape. Quantitative analysis of thick fiber arbor features showed little difference between the sides, although contralateral boutons were significantly larger than ipsilateral ones. Bouton distribution with respect to counterstained somata suggests that proximal dendrites are their main target. Indeed, ultrastructural examination demonstrated that they provide large diameter dendrites with numerous contacts. Direct comparison of thick fiber terminal arbors to cytochrome oxidase (CO) staining revealed that these arbors are much smaller than individual CO-rich patches believed to designate rods containing discrete body area representations. Thus, each terminal arbor appears to heavily innervate a small number of VPM neurons within a rod. This relationship would serve to maintain relatively small receptive fields within the topographic representation of the face.

The central mesencephalic reticular formation (cMRF) occupies much of the core of the midbrain tegmentum. Physiological studies indicate that it is involved in controlling gaze changes, particularly horizontal saccades. Anatomically, it receives input from the ipsilateral superior colliculus (SC) and it has downstream projections to the brainstem, including the horizontal gaze center located in the paramedian pontine reticular formation (PPRF). Consequently, it has been hypothesized that the cMRF plays a role in the spatiotemporal transformation needed to convert spatially coded collicular saccade signals into the temporally coded signals utilized by the premotor neurons of the horizontal gaze center. In this study, we used neuroanatomical tracers to examine the patterns of connectivity of the cMRF in macaque monkeys in order to determine whether the circuit organization supports this hypothesis. Since stimulation of the cMRF produces contraversive horizontal saccades and stimulation of the horizontal gaze center produces ipsiversive saccades, this would require an excitatory cMRF projection to the contralateral PPRF. Injections of anterograde tracers into the cMRF did produce labeled terminals within the PPRF. However, the terminations were denser ipsilaterally. Since the PPRF located contralateral to the movement direction is generally considered to be silent during a horizontal saccade, we then tested the hypothesis that this ipsilateral reticuloreticular pathway might be inhibitory. The ultrastructure of ipsilateral terminals was heterogeneous, with some displaying more extensive postsynaptic densities than others. Postembedding immunohistochemistry for gamma-aminobutyric acid (GABA) indicated that only a portion (35%) of these cMRF terminals are GABAergic. Dual tracer experiments were undertaken to determine whether the SC provides input to cMRF reticuloreticular neurons projecting to the ipsilateral pons. Retrogradely labeled reticuloreticular neurons were predominantly distributed in the ipsilateral cMRF. Anterogradely labeled tectal terminals were observed in close association with a portion of these retrogradely labeled reticuloreticular neurons. Taken together, these results suggest that the SC does have connections with reticuloreticular neurons in the cMRF. However, the predominantly excitatory nature of the ipsilateral reticuloreticular projection argues against the hypothesis that this cMRF pathway is solely responsible for producing a spatiotemporal transformation of the collicular saccade signal.