Amygdalo-nigral inputs target dopaminergic and GABAergic neurons in the primate: a view from dendrites and soma

The central nucleus (CeN) of the amygdala is an important afferent to the DA system that mediates motivated learning. We previously found that CeN terminals in nonhuman primates primarily overlap the elongated lateral VTA (parabrachial pigmented nucleus, PBP, A10), and retrorubral field(A8) subregion. Here, we examined CeN afferent contacts on cell somata and proximal dendrites of DA and GABA neurons, and distal dendrites of each, using confocal and electron microscopy (EM) methods, respectively. At the soma/proximal dendrites, the proportion of TH+ and GAD1+ cells receiving at least one CeN afferent contact was surprisingly similar (TH = 0.55: GAD1=0.55 in PBP; TH = 0.56; GAD1 =0.51 in A8), with the vast majority of contacted TH+ and GAD1+ soma/proximal dendrites received 1-2 contacts. Similar numbers of tracer-labeled terminals also contacted TH-positive and GAD1-positive small dendrites and/or spines (39% of all contacted dendrites were either TH- or GAD1-labeled). Overall, axon terminals had more symmetric (putative inhibitory) axonal contacts with no difference in the relative distribution in the PBP versus A8, or onto TH+ versus GAD1+ dendrites/spines in either region. The striking uniformity in the amygdalonigral projection across the PBP-A8 terminal field suggests that neither neurotransmitter phenotype nor midbrain location dictates likelihood of a terminal contact. We discuss how this afferent uniformity can play out in recently discovered differences in DA:GABA cell densities between the PBP and A8, and affect specific outputs.

Significance statement

The amygdala's central nucleus (CeN) channels salient cues to influence both appetitive and aversive responses via DA outputs. In higher species, the broad CeN terminal field overlaps the parabrachial pigmented nucleus ('lateral A10') and the retrorubral field (A8). We quantified terminal contacts in each region on DA and GABAergic soma/proximal dendrites and small distal dendrites. There was striking uniformity in contacts on DA and GABAergic cells, regardless of soma and dendritic compartment, in both regions. Most contacts were symmetric (putative inhibitory) with little change in the ratio of inhibitory to excitatory contacts by region.We conclude that post-synaptic shifts in DA-GABA ratios are key to understanding how these relatively uniform inputs can produce diverse effects on outputs.

Corticotropin-releasing factor-dopamine interactions in male and female macaque: Beyond the classic VTA

Dopamine (DA) is involved in stress and stress-related illnesses, including many psychiatric disorders. Corticotropin-releasing factor (CRF) plays a role in stress responses and targets the ventral midbrain DA system, which is composed of DA and non-DA cells, and divided into specific subregions. Although CRF inputs to the midline A10 nuclei ("classic VTA") are known, in monkeys, CRF-containing terminals are also highly enriched in the expanded A10 parabrachial pigmented nucleus (PBP) and in the A8 retrorubral field subregions. We characterized CRF-labeled synaptic terminals on DA (tyrosine hydroxylase, TH+) and non-DA (TH-) cell types in the PBP and A8 regions using immunoreactive electron microscopy (EM) in male and female macaques. CRF labeling was present mostly in axon terminals, which mainly contacted TH-negative dendrites in both subregions. Most CRF-positive terminals had symmetric profiles. In both PBP and A8, CRF symmetric (putative inhibitory) synapses onto TH-negative dendrites were significantly greater than asymmetric (putative excitatory) profiles. This overall pattern was similar in males and females, despite shifts in the size of these effects between regions depending on sex. Because stress and gonadal hormone shifts can influence CRF expression, we also did hormonal assays over a 6-month time period and found little variability in basal cortisol across similarly housed animals at the same age. Together our findings suggest that at baseline, CRF-positive synaptic terminals in the primate PBP and A8 are poised to regulate DA indirectly through synaptic contacts onto non-DA neurons.

Development of an Orthotopic Murine Model of Rectal Cancer in Conjunction With Targeted Short-Course Radiation Therapy

PURPOSE

Orthotopic tumors more closely recapitulate human cancers than do ectopic models; however, precision targeting of such internal tumors for radiation therapy (RT) without inducing systemic toxicity remains a barrier. We developed an innovative murine orthotopic rectal tumor model where the insertion of clinical grade titanium fiducial clips on opposing sides of the rectal tumor allowed for targeted administration of short-course radiation therapy (SCRT). With this novel approach, clinically relevant RT regimens can be administered to orthotopic tumors to explore the biology and efficacy of radiation alone or as a combination therapy in a murine model that closely recapitulates human disease.

METHODS AND MATERIALS

Murine Colon 38-luciferase tumor cells were injected into the rectal wall of syngeneic mice, and fiducial clips were applied to demarcate the tumor. An SCRT regimen consisting of 5 consecutive daily doses of 5 Gy delivered by an image-guided conformal small animal irradiator was administered 9 days after implantation. Tumor burden and survival were monitored along with histological and flow cytometric analyses on irradiated versus untreated tumors at various time points.

RESULTS

SCRT administered to orthotopic rectal tumors resulted in a reduction in tumor burden and enhanced overall survival with no apparent signs of systemic toxicity. This treatment paradigm resulted in significant reductions in tumor cellularity and increases in fibrosis and hyaluronic acid production, recapitulating the SCRT-induced effects observed in human cancers.

CONCLUSIONS

We have established a means to target murine orthotopic rectal tumors using fiducial markers with a fractionated and clinically relevant SCRT schedule that results in an RT response similar to what is observed in human rectal cancer. We also validated our model through examining various parameters associated with human cancer that are influenced by irradiation. This model can be used to further explore RT doses and scheduling, and to test combinatorial therapies.

J domain-independent regulation of the Rb family by polyomavirus large T antigen

The ability of polyomavirus large T antigen (LT) to promote cell cycling, to immortalize primary cells, and to block differentiation has been linked to its effects on tumor suppressors of the retinoblastoma susceptibility (Rb) gene family. Our previous studies have shown that LT requires an intact N-terminal DnaJ domain, in addition to an Rb binding site, for activation of simple E2F-containing promoters and stimulation of cell cycle progression. Here we show that some LT effects dependent on interaction with the Rb family are largely DnaJ independent. In differentiating C2C12 myoblasts, overexpression of LT caused apoptosis. Although this activity of LT completely depended on Rb binding, LTs with mutations in the J domain remained able to kill. Comparisons of Rb(-) and J(-) LTs revealed additional differences. Wild-type but not Rb(-) LT activated the cyclin A promoter under serum starvation conditions. Genetic analysis of the promoter linked the Rb requirement to an E2F site in the promoter. LTs with mutations in the J domain were still able to activate the promoter. Finally, J mutant LTs caused changes in phosphorylation of both pRb and p130. In the case of p130, Thr-986 was shown to be a site that is regulated by J mutant LT. Taken together, these observations reveal that LT regulation of Rb function can be separated into both DnaJ-dependent and DnaJ-independent pathways.