Distinct neuron populations for simple and compound calls in the primary auditory cortex of awake marmosets.

Marmosets are highly social non-human primates that live in families. They exhibit rich vocalization, but the neural basis underlying this complex vocal communication is largely unknown. Here we report the existence of specific neuron populations in marmoset A1 that respond selectively to distinct simple or compound calls made by conspecific marmosets. These neurons were spatially dispersed within A1 but distinct from those responsive to pure tones. Call-selective responses were markedly diminished when individual domains of the call were deleted or the domain sequence was altered, indicating the importance of the global rather than local spectral-temporal properties of the sound. Compound call-selective responses also disappeared when the sequence of the two simple-call components was reversed or their interval was extended beyond 1 s. Light anesthesia largely abolished call-selective responses. Our findings demonstrate extensive inhibitory and facilitatory interactions among call-evoked responses, and provide the basis for further study of circuit mechanisms underlying vocal communication in awake non-human primates.

Local homogeneity of tonotopic organization in the primary auditory cortex of marmosets.

Marmoset has emerged as a useful nonhuman primate species for studying brain structure and function. Previous studies on the mouse primary auditory cortex (A1) showed that neurons with preferential frequency-tuning responses are mixed within local cortical regions, despite a large-scale tonotopic organization. Here we found that frequency-tuning properties of marmoset A1 neurons are highly uniform within local cortical regions. We first defined the tonotopic map of A1 using intrinsic optical imaging and then used in vivo two-photon calcium imaging of large neuronal populations to examine the tonotopic preference at the single-cell level. We found that tuning preferences of layer 2/3 neurons were highly homogeneous over hundreds of micrometers in both horizontal and vertical directions. Thus, marmoset A1 neurons are distributed in a tonotopic manner at both macro- and microscopic levels. Such organization is likely to be important for the organization of auditory circuits in the primate brain.

Cerebellar interpositus nuclear inputs impinge on paraventricular neurons of the hypothalamus in rats.

Several reports have indicated that the cerebellum is involved in regulation of some non-somatic activities through the cerebellohypothalamic projections. Therefore, the modulatory effects of the cerebellar interpositus nucleus (IN) on neuronal activity of the paraventricular nucleus of the hypothalamus (PVN) was investigated in this study by using in vivo extracellular recording technique in rats. We recorded from 115 PVN neurons, 51 (44.3%) responded to the cerebellar IN stimulation. Of the responsive PVN neurons tested for their sensitivity to hypertensive and/or hyperosmotic stimulations, 66.7% (6/9) and 75.0% (6/8) responded to intravenous metaraminol and hypertonic saline administration, respectively. These results demonstrate that the cerebellar IN afferent inputs impinge on the PVN neurons, including those baroreflex-sensitive and osmoresponsive neurons, suggesting that the cerebellum may actively participate in the cardiovascular regulation and osmoregulation through the cerebellohypothalamic projections.

Convergence of gastric vagal and cerebellar fastigial nuclear inputs on glycemia-sensitive neurons of lateral hypothalamic area in the rat.

Gastric vagal and cerebellar fastigial nuclear afferents have been implicated in the regulation of food intake by their communication with lateral hypothalamic area (LHA), which is generally referred to be the feeding center. This study was designed to examine the possible convergence of the inputs from the gastric vagal trunks and cerebellar fastigial nucleus (FN) on the LHA neurons. Among recorded 191 LHA neurons, 99 (51.8%) responded to the stimulation of the gastric vagal trunks, of which 55 (55.6%) also responded to the cerebellar FN stimulation. Of 62 LHA neurons that responded to the gastric vagal stimulation, 43 (69.4%) showed an inhibitory response to the intravenous glucose application indicating they were glycemia-sensitive neurons. When the gastric vagal trunks and cerebellar FN were stimulated simultaneously, a summation of the responses usually could be seen in the recorded LHA neurons (16/20, 80%). Moreover, of 45 LHA neurons that responded to both of the gastric vagal trunks and FN stimuli, 30 (66.7%) were identified to be glycemia-sensitive neurons. These results demonstrated that gastric vagal afferents could reach glycemia-sensitive neurons of the LHA, and that the inputs from cerebellar FN and gastric vagal trunks could converge onto glycemia-sensitive neurons in the LHA. According to the facts that gastric vagal inputs and blood glucose level may transmit meal-related visceral signals and FN may forward the somatic information to the LHA, we suggest that an integration of the somatic-visceral response related to the food intake may take place in the LHA following the gastric vagal and cerebellar FN afferent inputs and the integration may play an important role in the short-term regulation of feeding behavior.