Cytoarchitecture and topographic projections of the gustatory centers in a teleost, Carassius carassius

Abstract

The neuronal connections in the central gustatory system of the crucian carp were examined by means of degeneration and HRP methods. Cell morphology in the primary gustatory lobes was studied in Golgi-impregnated material. Medium-sized neurons of the facial lobe emit axons which project to the secondary gustatory nucleus. The nucleus intermedius facialis of Herrick ('05) projects bilaterally. Large neurons send axons through the spinal trigeminal tract to terminate in the spinal trigeminal nucleus and in the medial funicular nucleus. In the vagal lobe, second-order neurons for the ascending projections are located in the superficial part of the sensory zone. These neurons project exclusively to the ipsilateral secondary gustatory nucleus. Neurons located in the deeper part of the sensory zone send axons to the motor zone and to the brainstem reticular formation to form short reflex arcs. The glossopharyngeal lobe has similar neuronal connections to the vagal sensory zone. Both facial and vagal lobes receive afferent projections from the following central structures: nucleus posterioris thalami, nucleus diffusus lobi inferioris, optic tectum, motor nucleus of the trigeminal nerve, medullary reticular formation, and the gray matter of the upper spinal cord. The facial lobe has an additional afferent from the mesencephalic reticular formation. The major sources to the medullary gustatory lobes are the nucleus posterioris thalami and nucleus diffusus lobi inferioris. Each type of neuron classified by morphology and location in the facial, glossopharyngeal, and vagal lobes was correlated with its particular destination. Topographic projections were demonstrated in the secondary and tertiary gustatory centers.

The tertiary gustatory center in sunfishes is not nucleus glomerulosus

“…The efferent projections of the secondary gustatory nucleus in Lepomis show essentially the same pattern of tertiary gustatory connections in percomorphs as has been demonstrated for cyprinids [5,6] and silurids [2]. It is surprising, that while the secondary gustatory nucleus is much smaller in Lepornis than it is in cyprinids or silurids, the tertiary gustatory nucleus is of similar dimension.…”

“…Although a histologically comparable nucleus cannot be recognized in cypriniform teleosts, attempts have been made to identify a homologous structure within the preglomerular complex of the latter teleosts. For example, a 'nucleus glomerulosus' in the crucian carp, Carassius carassius, has been shown to receive a tertiary gustatory projection after lesioning of, or horseradish peroxidase (HRP) injections into, the secondary gustatory nucleus [5,6]. If nucleus glomerulosus of percomorphs is homologous to this tertiary gustatory center demonstrated in Carassius, then it would consequently be expected to receive a substantial projection from the secondary gustatory nucleus.…”

“…1A, 2A,B and 3), which lies immediately rostral to the posterior part of nucleus glomerulosus. This preglomerular division has been termed nucleus glomerulosus in Carassius carassius [5,6], but some authors have questioned the implied homology to the percomorph nucleus glomerulosus by using quotation marks for 'glomerulosus' [1]. The present paper will refer to it as nucleus gustatorius tertius.…”

Fiber Connections of the Inferior Lobe in a Percomorph Teleost, <i>Thamnaconus (Navodon) modestus</i>

“…Involvement of this area in the control of feeding and aggressive behavior has been suggested by electrical stimulation experiments in cichlids [Demski and Knigge, 1971;Demski, 1973]. Gustatory inputs to this structure have been reported in acanthopterygian teleosts [sunfish : Wullimann, 1988;tilapia: Yoshimoto et al, 1998] and in ostariophysan teleosts [catfish: Kanwal et al, 1988;Lamb and Caprio, 1993;Lamb and Finger, 1996; crucian carp: Morita et al, 1980Morita et al, , 1983 for review see Meek and Nieuwenhuys, 1998]. In an acanthopterygian teleost Thamnaconus, visual inputs via the corpus glomerulosum (CG) to the inferior lobe have also been reported [Sakamoto and Ito, 1982].…”

Afferent and Efferent Connections of the Dorsocentral Telencephalon in an Electrosensory Teleost, <i>Gymnotus carapo</i>

“…In teleosts the hypothalamus is the target of multisensory convergence [Finger, 1980;Morita et al, 1980Morita et al, , 1983Wulliman, 1988;Striedter, 1990]. Keller et al [1990] identified projections from nucleus electrosensorius in the inferior lobe of Eigenmania.…”