Afferent connections of the parabrachial nucleus in C57BL/6J mice

Abstract

Although the mouse is an experimental model with an increasing importance in various fields of Neuroscience, the characteristics of its central gustatory pathways have not yet been well documented. Recent electrophysiological studies using the rat and hamster have revealed that taste processing in the brainstem gustatory relays is under the strong influence of inputs from forebrain gustatory structures. In the present study, we investigated the organization of afferent projections to the mouse parabrachial nucleus (PbN), which is located at a key site between the brainstem and gustatory, viscerosensory and autonomic centers in the forebrain. We made injections of the retrograde tracer Fluorogold centered around the "waist" area of the PbN, whose neurons are known to be highly responsive to taste stimuli. Retrogradely labeled neurons were found in the infralimbic, dysgranular and agranular insular cortex as well as the claustrum; the bed nucleus of the stria terminalis and the substantia innominata; the central nucleus of the amygdala; the lateral and medial preoptic areas, the paraventricular, the dorsomedial, the ventromedial, the arcuate, and the lateral hypothalamic areas; the periaqueductal gray, the substantia nigra pars compacta, and the ventral tegmental area; the supratrigeminal nucleus, rostral and caudal nucleus of the solitary tract; the parvicellular intermediate and gigantocellular reticular nucleus; the caudal and interpolar divisions of the spinal trigeminal nucleus, dorsomedial spinal trigeminal nucleus, and the area postrema. Numbers of labeled neurons in the main components of the gustatory system including the insular cortex, bed nucleus of the stria terminalis, central nucleus of the amygdala, lateral hypothalamus, and rostral nucleus of the solitary tract were quantified. These results are basically consistent with those of the previous rat and hamster studies, but some species differences were found. Functional implications of these afferent inputs are discussed with an emphasis on their role in taste.Keywords taste system; cortex; amygdala; hypothalamus; bed nucleus of the stria terminalis; nucleus of the solitary tract

Gustatory neural responses to umami stimuli in the parabrachial nucleus of C57BL/6J mice

“…Moreover, decerebration at the level of the superior colliculus decreased PbN spontaneous firing rates in rats (Tokita et al 2004). The mouse PbN receives dense projections from taste-related structures in the forebrain (Tokita et al 2009). Finally it should be also noted that the anesthetic used might have an influence on spontaneous neural activity.…”

“…This also represents the first investigation into physiological characteristics of taste-responsive neurons in this brainstem area in this species, a key interface between brainstem and forebrain gustatory areas (Tokita et al 2009;. Neurophysiological investigations into the mouse central taste system have begun only recently, including two recent studies on taste-response properties in neurons in the NST (McCaughey 2007;Lemon and Margolskee 2009).…”

Sensory regulation of dopaminergic cell activity: Phenomenology, circuitry and function

“…Indeed, existing evidence suggests that the lateral habenula may provide information to DA neurons concerning aversive, non-noxious stimuli (Matsumoto and Hikosaka, 2007). If information about noxious stimuli is provided by the PBN (which does not receive an input from the lateral habenula, Tokita et al, 2009), this suggests that signals concerning these two types of negative outcome may be provided to DA neurons by different circuitry, an observation which is likely to be important for the debate about the neural separation of different classes of punishment signal (e.g. Boksem et al, 2008).…”

“…As well as receiving nociceptive information from the spinal cord, the PBN also receives inputs from widespread areas of the brain (Tokita et al 2009), including the rostral part of nucleus of the solitary tract (Herbert et al, 1990), a brain area involved in the processing of gustatory information (Norgren and Leonard, 1973). Gustatory processing in the PBN is normally associated with an area which includes aspects of the lateral and medial subnuclei surrounding the superior cerebellar peduncle, as well as neurons within it (Karimnamazi and Travers 1998), all of which according to our retrograde anatomical results project to the SNc and VTA.…”

Characterizing the neuropeptide pathways between the forebrain and the pons.

“…The current state of knowledge indicates striking similarity in the anatomical connectivity of the PBN and ventral forebrain in mice compared to rats and hamsters. That is, neurons in the mouse PBN are reciprocally connected to the CeA, BNST, and LH (Tokita et al, 2009;Tokita et al, 2010). The neurochemical cell types that comprise these centrifugal pathways have not yet been elucidated.…”