It is becoming increasingly clear that the brain processes sensory stimuli differently according to whether they are passively or actively acquired, and these differences can be seen early in the sensory pathway. In the nucleus of the solitary tract (NTS), the first relay in the central gustatory neuraxis, a rich variety of sensory inputs generated by active licking converge. Here we show that taste responses in the NTS reflect these interactions. Experiments consisted of recordings of taste-related activity in the NTS of awake rats as they freely licked exemplars of the five basic taste qualities (sweet, sour, salty, bitter, umami). Nearly all taste-responsive cells were broadly tuned across taste qualities. A subset responded to taste with long latencies (>1.0 s), suggesting the activation of extra-oral chemoreceptors. Analyses of the temporal characteristics of taste responses showed that spike timing conveyed significantly more information than spike count alone in almost half of NTS cells, as in anesthetized rats, but with less information per cell. In addition to taste-responsive cells, the NTS contains cells that synchronize with licks. Since the lick pattern per se can convey information, these cells may collaborate with taste-responsive cells to identify taste quality. Other cells become silent during licking. These latter “anti-lick” cells show a surge in firing rate predicting the beginning and signaling the end of a lick bout. Collectively, the data reveal a complex array of cell types in the NTS, only a portion of which include taste-responsive cells, which work together to acquire sensory information.

Loneliness, the subjective experience of social isolation, may reflect, in part, underlying neural processing of social signals. Aging may exacerbate loneliness due to decreased social networks and increased social isolation, or it may reduce loneliness due to preferential attentional processing of positive information and increased interactions with emotionally close partners. Here, we conducted a functional magnetic resonance imaging (fMRI) study of loneliness in younger (N = 50, 26 female, M = 20.4) and older (N = 49, 30 female, M = 62.9) adults. Compared to younger adults, older adults were less lonely and dwelled longer on faces, regardless of valence. Previous studies in younger adults found that loneliness was negatively correlated with ventral striatal (VS) activation to pleasant social pictures of strangers yet positively correlated with VS activation to faces of close others. In the present study, we observed no association between loneliness and VS activation to social pictures of strangers in either age group. Further, unlike previous studies, we observed no association between social network size and amygdala activation to social stimuli. Additional research is needed to examine the effect of loneliness and social network size on neural processing of different dimensions of social stimuli.

Sex differences and gonadal hormone influences are well known for diverse aspects of forebrain amine and indolamine neurotransmitter systems, the cognitive and affective functions they govern and their malfunction in mental illness. This study explored whether hormone regulation/ dysregulation of these systems could be related to gonadal steroid effects on catechol-Omethyltransferase and monoamine oxidase which are principal enzymatic controllers of forebrain dopamine, serotonin and norepinephrine levels. Driven by male over female differences in cortical enzyme activities, by male-specific associations between monoamine oxidase and catechol-Omethyltransferase gene polymorphisms and cognitive and dysfunction in disease and by malespecific consequences of gene knockouts in mice, the question of hormone sensitivity was addressed here using a male rat model where prefrontal dopamine levels and related behaviors are also known to be affected. Specifically, quantitative O-methylation and oxidative deamination assays were used to compare the activities of catechol-O-methyltransferase's soluble and membrane-bound isoforms and of monoamine oxidase's A and B isoforms in the pregenual medial prefrontal cortex and dorsal striatum of male rats that were sham operated, gonadectomized or gonadectomized and supplemented with testosterone propionate or with estradiol for 28 days. These studies revealed significant effects of hormone replacement but not gonadectomy on the soluble but not the membrane-bound isorfom of catechol-O-methyltransferase in both striatum and cortex. A significant, cortex-specific testosterone-but not estradiol-attenuated effect (increase) of gonadectomy on monoamine oxidase's A but not B isoform was also observed. Although none of these actions suggest potential roles in the reguation/dysregulation of prefrontal dopamine, the suppressive effects of testosterone on cortical monoamine oxidase-A that were observed could have bearing on the increased incidence of cognitive deficits and symptoms of depression and anxiety that are repeatedly observed in males in conditions of hypogonadalism related to aging, other biological factors or in prostate cancer where androgen deprivation is used as a neoadjuvant treatment. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author ManuscriptNeuroscience. Author manuscript; available in PMC 2011 February 3. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptThe prefrontal cortices are essential in mediating highest order executive functions such as planning, working memory and behavi...

Prospective studies using [C]harmine are possible given its test-retest repeatability when binding is quantified using arterial blood. Results with SIME of input function show potential for simplifying data acquisition by replacing arterial catheterization with one arterial blood sample at 20 min post-injection. Estimation of [C]harmine binding potentials remains a challenge that warrants further investigation.