Cajal's nucleus of the stria medullaris: characterization by in situ hybridization and immunohistochemistry for enkephalin

The Neuromeric/Prosomeric Model in Teleost Fish Neurobiology

The neuromeric/prosomeric model has been rejuvenated by Puelles and Rubenstein [Trends Neurosci. 1993;16(11):472-9]. Here, its application to the (teleostean) fish brain is detailed, beginning with a historical account. The second part addresses three main issues with particular interest for fish neuroanatomy and looks at the impact of the neuromeric model on their understanding. The first one is the occurrence of four early migrating forebrain areas (M1 through M4) in teleosts and their comparative interpretation. The second issue addresses the complex development and neuroanatomy of the teleostean alar and basal hypothalamus. The third topic is the vertebrate dopaminergic system, with the focus on some teleostean peculiarities. Most of the information will be coming from zebrafish studies, although the general ductus is a comparative one. Throughout the manuscript, comparative developmental and organizational aspects of the teleostean amygdala are discussed. One particular focus is cellular migration streams into the medial amygdala.

Untangling the dorsal diencephalic conduction system: a review of structure and function of the stria medullaris, habenula and fasciculus retroflexus

The often-overlooked dorsal diencephalic conduction system (DDCS) is a highly conserved pathway linking the basal forebrain and the monoaminergic brainstem. It consists of three key structures; the stria medullaris, the habenula and the fasciculus retroflexus. The first component of the DDCS, the stria medullaris, is a discrete bilateral tract composed of fibers from the basal forebrain that terminate in the triangular eminence of the stalk of the pineal gland, known as the habenula. The habenula acts as a relay hub where incoming signals from the stria medullaris are processed and subsequently relayed to the midbrain and hindbrain monoaminergic nuclei through the fasciculus retroflexus. As a result of its wide-ranging connections, the DDCS has recently been implicated in a wide range of behaviors related to reward processing, aversion and motivation. As such, an understanding of the structure and connections of the DDCS may help illuminate the pathophysiology of neuropsychiatric disorders such as depression, addiction and pain. This is the first review of all three components of the DDCS, the stria medullaris, the habenula and the fasciculus retroflexus, with particular focus on their anatomy, function and development.

Left Habenula Mediates Light-Preference Behavior in Zebrafish via an Asymmetrical Visual Pathway

Habenula (Hb) plays critical roles in emotion-related behaviors through integrating inputs mainly from the limbic system and basal ganglia. However, Hb also receives inputs from multiple sensory modalities. The function and underlying neural circuit of Hb sensory inputs remain unknown. Using larval zebrafish, we found that left dorsal Hb (dHb, a homolog of mammalian medial Hb) mediates light-preference behavior by receiving visual inputs from a specific subset of retinal ganglion cells (RGCs) through eminentia thalami (EmT). Loss- and gain-of-function manipulations showed that left, but not right, dHb activities, which encode environmental illuminance, are necessary and sufficient for light-preference behavior. At circuit level, left dHb neurons receive excitatory monosynaptic inputs from bilateral EmT, and EmT neurons are contacted mainly by sustained ON-type RGCs at the arborization field 4 of retinorecipient brain areas. Our findings discover a previously unidentified asymmetrical visual pathway to left Hb and its function in mediating light-preference behavior. VIDEO ABSTRACT.

A premammillary lateral hypothalamic nuclear complex responds to hedonic but not aversive tastes in the male rat

The lateral hypothalamic area (LHA) has two major roles: arousal/waking and food intake controls. Here, it is shown that a premammillary part of the LHA is neurochemically and cytoarchitectonically distinct from the tuberal LHA in male rats. This part contains nuclear masses, namely the parasubthalamic nucleus and the calbindin nucleus, involved in pathways that predict its participation in the control of food intake. Analyzing c-Fos expression in experiments related to feeding behavior, this region responded specifically to the ingestion of palatable nutriments.

The distribution of GAD67-mRNA in the adult zebrafish (teleost) forebrain reveals a prosomeric pattern and suggests previously unidentified homologies to tetrapods

We used in situ hybridization on sections to examine the distribution of GAD67-expressing cell populations in the entire forebrain of the adult zebrafish. GAD67 is predominantly expressed in the olfactory bulb (OB), all regions of the subpallium (including the dorsal, ventral, central, and lateral nucleus of the area ventralis [Vd, Vv, Vc, and Vl, respectively]), as well as preoptic (PPa, PPp, and PM), pretectal (PPd, PPv, PCN, PSp, and PSm), ventral (= pre-) thalamic (I, VM, and VL), hypothalamic (Hr, Hi, and Hc), preglomerular (P, PGa, PGl, PGm, and RT), and posterior tubercular (TPp and TPm) nuclei. Only scattered GAD67-expressing cells are seen in all pallial zones (Dm, Dd, Dc, Dl, and Dp) and in the previously unidentified bed nucleus of the stria medullaris (BNSM). The BNSM appears to be the adult teleostean derivative of the larval eminentia thalami (EmT). We identify the GAD67-positive entopeduncular nucleus proper (EN) as being homologous to the entopeduncular nucleus of nonprimate mammals. GAD67 is strongly expressed in the anterior thalamic nucleus (A). The anterior thalamic nucleus is laterally bordered by a distinct GAD67-expressing cell population, which we interpret as the previously unidentified reticular thalamic nucleus (RTN) of teleosts. Furthermore, we identified a GAD67-positive thalamic nucleus, the intercalated nucleus (IC), which is sandwiched between the GAD67-negative dorsal (DP) and central posterior (CP) thalamic nuclei. Overall, the distribution of GAD67-expressing cells highly resembles the distribution of gamma-aminobutyric acid (GABA)/GAD67-expressing cells found in the early zebrafish (teleost) forebrain and thus allows us to propose a prosomeric fate map of GABAergic cell populations.

The structural organization of connections between hypothalamus and cerebral cortex

Motivated behavior requires coordinated somatic, autonomic, and endocrine responses, and may be divided into initiation, procurement, and consummatory phases (Swanson, L.W. and Mogenson, G.J., Neural mechanisms for the functional coupling of autonomic, endocrine and somatomotor responses in adaptative behavior, Brain Res. Rev., 3 (1981) 1-34). Obviously, such behavior may involve the entire central nervous system, although it is important to identify circuitry or systems that mediate the behavior directed toward specific goal objects. This problem has recently been clarified by the identification of hypothalamic subsystems important for the execution of instinctive behaviors related to ingestion, reproduction, and defense. These subsystems are modulated by sensory (reflex), central control (e.g., circadian), and voluntary (cortical) inputs. The latter are dominated by inputs from the ventral temporal lobe and medial prefrontal region, which are both direct and via associated parts of the basal nuclei (ganglia). Hypothalamic output is characterized by descending projections to brainstem and spinal motor systems, and by projections back to the cerebral cortex, which are both direct and via a continuous rostromedial part of the dorsal thalamus. This thalamic region includes the anterior, medial, and midline groups, which in turn innervate a continuous ring of cortex that includes the hippocampal formation and the cingulate, prefrontal, and insular regions. Parts of this thalamic region also innervate the ventral striatum, which receives a massive input from the cortical rings as well.

Chemoarchitecture of the rat lateral septal nucleus

The distribution of neurons and terminal fields that contain a variety of neurotransmitters and steroid hormone receptors has been examined with in situ hybridization and immunohistochemistry in closely spaced series of sections throughout the rostrocaudal extent of the rat lateral septal nucleus, as well as the adjacent septohippocampal and septofimbrial nuclei. The results indicate that the lateral septal nucleus is divided into major rostral, caudal, and ventral parts that differ from the widely used cytoarchitectonic parcellation into dorsal, intermediate, and ventral parts. Furthermore, the rostral, caudal, and ventral parts are turn divided into about 20 zones, regions, and domains on the basis of differential terminal fields and neurons that express particular neuropeptides and steroid hormone receptors. In general, the small zones and regions form dorsoventrally oriented sheets or bands that are arranged in a complex way. Differential connections of these lateral septal components are analyzed in the accompanying paper (Risold, P. Y. and Swanson, L. W., Connections of the rat lateral septal complex, Brain Res. Rev., 24 (1997) 115-195).