Functional circuitry involved in the regulation of whisker movements

Abstract

Neuroanatomical tract-tracing methods were used to identify the oligosynaptic circuitry by which the whisker representation of the motor cortex (wMCx) influences the facial motoneurons that control whisking activity (wFMNs). Injections of the retrograde tracer cholera toxin subunit B into physiologically identified wFMNs in the lateral facial nucleus resulted in dense, bilateral labeling throughout the brainstem reticular formation and in the ambiguus nucleus as well as predominantly ipsilateral labeling in the paralemniscal, pedunculopontine tegmental, Kölliker-Fuse, and parabrachial nuclei. In addition, neurons in the following midbrain regions projected to the wFMNs: superior colliculus, red nucleus, periaqueductal gray, mesencephalon, pons, and several nuclei involved in oculomotor behaviors. Injections of the anterograde tracer biotinylated dextran amine into the wMCx revealed direct projections to the brainstem reticular formation as well as multiple brainstem and midbrain structures shown to project to the wFMNs. Regions in which retrograde labeling and anterograde labeling overlap most extensively include the brainstem parvocellular, gigantocellular, intermediate, and medullary (dorsal and ventral) reticular formations; ambiguus nucleus; and midbrain superior colliculus and deep mesencephalic nucleus. Other regions that contain less dense regions of combined anterograde and retrograde labeling include the following nuclei: the interstitial nucleus of medial longitudinal fasciculus, the pontine reticular formation, and the lateral periaqueductal gray. Premotoneurons that receive dense inputs from the wMCx are likely to be important mediators of cortical regulation of whisker movements and may be a key component in a central pattern generator involved in the generation of rhythmic whisking activity. Keywordscentral pattern generator; motor cortex; facial nucleus; brainstem; rat Production of rhythmic whisker movements ("whisking") is a critical exploratory behavior in several mammalian species (see, e.g., Vincent, 1912;Brecht et al., 1997) and is emerging as a model system for studying mechanisms of voluntary movements (Kleinfeld et al., 1997). Whisking consists of large-amplitude protractions of the large mystacial vibrissae, with spectral components between 6 and 9 Hz (Semba and Komisaruk, 1984). The whisker representation of the motor cortex (wMCx) occupies approximately one-third of the rodent motor cortex, and low-intensity stimulation of this region evokes whisker protractions (Donoghue and Wise, 1982;Weiss and Keller, 1994). The patterns of afferent, efferent, and intracortical connections of the wMCx suggest that the area is devoted primarily to regulating whisker movements (Donoghue and Parham, 1983;Miyashita et al., 1994;Weiss and Keller, 1994). However, the mechanisms by which the wMCx regulates whisking are at present unknown. Support for a role of the wMCx in regulating whisking is derived from studies demonstrating correlations between wMCx unit activity and EMG recorded from the whis...

Facial nerve injuries cause changes in central nervous system microglial cells

“…Tampoco se presentaron diferencias entre los grupos en cuanto al patrón de distribución celular ni en el número de células por campo (t (6) =1,16; p=0,29), o en el área ocupada por las mismas (t (6) =0,89; p=0,41).…”

“…Los músculos asociados a los movimientos de las vibrisas son controlados por motoneuronas cuyos somas se ubican en el núcleo facial, las cuales, a su vez, están comandadas por múltiples estructuras premotoras (6). En la corteza cerebral, las células piramidales de la capa V de la corteza motora agranular medial, o corteza motora primaria de las vibrisas (Vibrissal Motor Cortex, vM1), actúan mediante proyecciones monosinápticas directas sobre las motoneuronas del núcleo del nervio facial que comandan el movimiento de las vibrisas (neuronas córtico-faciales) (7).…”

Cellular mechanisms of motor control in the vibrissal system

“…3b-e) [34] may predispose facial nucleus motor neurons to rhythmic discharges. Facial nucleus neurons receive direct sensory input from trigeminal brainstem neurons [35], as well as widespread inputs from other motor centers, some of which will be discussed below [36].…”

“…The persistence of whisking after removal of the entire cerebral cortex primed researchers to look for a subcortical whisking CPG. Thus, anatomical [36] and physiological/pharmacological [34] studies delineated brain stem circuits involved in the control of whisking. Brainstem neurons, including serotonergic cells that provide inputs to the whisking motor neurons in the facial nucleus, may form the brainstem pattern generator for whisking.…”

Retracción a largo plazo del árbol dendrítico de neuronas piramidales córtico-faciales por lesiones periféricas del nervio facial

“…Estas motoneuronas reciben comandos monosinápticos de células piramidales córtico-faciales de la capa V de la corteza motora primaria de las vibrisas (4) y de otras estructuras premotoras troncoencefálicas (5). Cuando las vibrisas se baten e interaccionan con objetos, la inflexión provocada en las mismas es transformada por mecanorreceptores en patrones espacio-temporales de actividad neuronal (6), que son conducidos por la rama infraorbitaria del nervio trigémino (7,8).…”