Schreiner organs: A new craniate chemosensory modality in hagfishes

Abstract

An extensive system of sensory organs resembling taste buds was previously known in the skin of hagfishes. These sensory organs, called here Schreiner organs, are found throughout the epidermis of both Eptatretus stoutii and Myxine glutinosa. They are found also at high densities in the prenasal sinus, nasopharyngeal duct, and pharynx, and at lower densities in the oral and velar chambers. Schreiner organs are multicellular aggregates composed of acetylated tubulin-immunoreactive receptor cells and nonimmunoreactive cells. A considerable range of variation was found in Schreiner organ morphology, but discrete classes of organs could not be recognized. Schreiner organs are innervated by all sensory trigeminal rami, the glossopharyngeal/vagal nerve, and cutaneous rami of spinal nerves, but not by the facial nerve. The central projections of these rami form a continuous tract in the trigeminal sensory zone and the dorsolateral funiculus of the spinal cord. Some Schreiner organs may be represented in the nucleus of the solitary tract, but this structure is certainly not the primary recipient zone of Schreiner organ afferents. In light of these systemic differences between vertebrate taste systems and the Schreiner organ system of hagfishes, it is concluded that Schreiner organs are not homologous to taste buds. This sensory modality of hagfishes has no direct homolog in vertebrates and appears to be a specialization of hagfishes, perhaps derived from the primitive somatosensory system of the earliest craniates.

Solitary chemoreceptor cells in the nasal cavity serve as sentinels of respiration

“…For example, the nasal epithelium of hagfish is replete with such cells (22), as is the olfactory epithelium of goldfish (23). The SCCs of nonmammalian vertebrates, like the gustducin-immunoreactive cells of the nasal cavity in rodents, form intimate, embracing contacts with branched nerve processes (21), many of which can arise from the In this example, on application of cycloheximide, the steady prestimulus rate is drastically reduced to a near apnea (rate is less than one breath per 10 sec.).…”

“…trigeminal nerve (22). Despite the phylogenetically wide abundance of SCCs throughout the nonmammalian vertebrates, such cells are not generally described for mammals.…”

A Trajectory of Increasing Activity and the Elaboration of Chemosensory Modality: A New Perspective on Vertebrate Origins

“…Gnathostomes are endowed with olfactory, gustatory, and solitary chemosensory systems (reviewed by Finger, 1997;Northcutt, 2004). Lampreys and hagfishes possess an olfactory system, while hagfishes lack taste-bud homologues (Braun, 1998;Northcutt, 2004). Instead, hagfishes possess an evolutionarily distinct chemosensory system, the so-called Schreiner system (Braun, 1998).…”

“…Lampreys and hagfishes possess an olfactory system, while hagfishes lack taste-bud homologues (Braun, 1998;Northcutt, 2004). Instead, hagfishes possess an evolutionarily distinct chemosensory system, the so-called Schreiner system (Braun, 1998). Similar to taste buds, the Schreiner organs are multicellular, and they are not only distributed in the oropharyngeal epithelium, but also on the body surface (Braun, 1998).…”

“…Instead, hagfishes possess an evolutionarily distinct chemosensory system, the so-called Schreiner system (Braun, 1998). Similar to taste buds, the Schreiner organs are multicellular, and they are not only distributed in the oropharyngeal epithelium, but also on the body surface (Braun, 1998). One of the most distinct differences between gustatory and Schreiner systems is that taste buds are innervated by sensory branches of the facial (VII), glossopharyngeal (IX), and vagus (X) nerves, whereas the Schreiner system adds the trigeminal (V) nerve as a component.…”