Complex animal behaviors are built from dynamical relationships between sensory inputs, neuronal activity, and motor outputs in patterns with strategic value. Connecting these patterns illuminates how nervous systems compute behavior. Here, we study Drosophila larva navigation up temperature gradients toward preferred temperatures (positive thermotaxis). By tracking the movements of animals responding to fixed spatial temperature gradients or random temperature fluctuations, we calculate the sensitivity and dynamics of the conversion of thermosensory inputs into motor responses. We discover three thermosensory neurons in each dorsal organ ganglion (DOG) that are required for positive thermotaxis. Random optogenetic stimulation of the DOG thermosensory neurons evokes behavioral patterns that mimic the response to temperature variations. In vivo calcium and voltage imaging reveals that the DOG thermosensory neurons exhibit activity patterns with sensitivity and dynamics matched to the behavioral response. Temporal processing of temperature variations carried out by the DOG thermosensory neurons emerges in distinct motor responses during thermotaxis.

The evolutionary expansion of sensory neuron populations detecting important environmental cues is widespread, but functionally enigmatic. We investigated this phenomenon through comparison of homologous neural pathways of Drosophila melanogaster and its close relative Drosophila sechellia, an extreme specialist for Morinda citrifolia noni fruit. D. sechellia has evolved species-specific expansions in select, noni-detecting olfactory sensory neuron (OSN) populations, through multigenic changes. Activation and inhibition of defined proportions of neurons demonstrate that OSN population increases contribute to stronger, more persistent, noni-odor tracking behavior. These sensory neuron expansions result in increased synaptic connections with their projection neuron (PN) partners, which are conserved in number between species. Surprisingly, having more OSNs does not lead to greater odor-evoked PN sensitivity or reliability. Rather, pathways with increased sensory pooling exhibit reduced PN adaptation, likely through weakened lateral inhibition. Our work reveals an unexpected functional impact of sensory neuron expansions to explain ecologically-relevant, species-specific behavior.

Olfactory receptor neurons (ORNs) convey sensory information directly to the CNS via conventional glutamatergic synaptic contacts in olfactory bulb glomeruli. To better understand the process by which information contained in the odorant-evoked firing of ORNs is transmitted to the brain, we examined the properties of glutamate release from olfactory nerve (ON) terminals in slices of the rat olfactory bulb. We show that marked paired pulse depression is the same in simultaneously recorded periglomerular and tufted neurons, and that this form of short-term plasticity is attributable to a reduction of glutamate release from ON terminals. We used the progressive blockade of NMDA receptor (NMDAR) EPSCs by MK-801 [(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-10-imine hydrogen maleate] and stationary fluctuation analysis of AMPA receptor (AMPAR) EPSCs to determine the probability of release (P(r)) of ON terminals; both approaches indicated that P(r) is unusually high (>/=0.8). The low-affinity glutamate receptor antagonists gamma-d-glutamylglycine and l-amino-5-phosphonovaleric acid blocked ON-evoked AMPAR- and NMDAR-mediated EPSCs, respectively, to the same extent under conditions of low and high P(r), suggesting that multivesicular release is not a feature of ON terminals. Although release from most synapses exhibits a highly nonlinear dependence on extracellular Ca(2+), we find that the relationship between glutamate release and extracellular Ca(2+) at ON terminals is nearly linear. Our results suggest that ON terminals have specialized features that may contribute to the reliable transmission of sensory information from nose to brain.

Females of many animal species behave very differently before and after mating. In Drosophila melanogaster, changes in female behavior upon mating are triggered by the sex peptide (SP), a small peptide present in the male's seminal fluid. SP activates a specific receptor, the sex peptide receptor (SPR), which is broadly expressed in the female reproductive tract and nervous system. Here, we pinpoint the action of SPR to a small subset of internal sensory neurons that innervate the female uterus and oviduct. These neurons express both fruitless (fru), a marker for neurons likely to have sex-specific functions, and pickpocket (ppk), a marker for proprioceptive neurons. We show that SPR expression in these fru+ ppk+ neurons is both necessary and sufficient for behavioral changes induced by mating. These neurons project to regions of the central nervous system that have been implicated in the control of reproductive behaviors in Drosophila and other insects.

The complete sequence of the 16,295 bp mouse L cell mitochondrial DNA genome has been determined. Genes for the 12S and 16S ribosomal RNAs; 22 tRNAs; cytochrome c oxidase subunits I, II and III; ATPase subunit 6; cytochrome b; and eight unidentified proteins have been located. The genome displays exceptional economy of organization, with tRNA genes interspersed between rRNA and protein-coding genes with zero or few noncoding nucleotides between coding sequences. Only two significant portions of the genome, the 879 nucleotide displacement-loop region containing the origin of heavy-strand replication and the 32 nucleotide origin of light-strand replication, do not encode a functional RNA species. All of the remaining nucleotide sequence serves as a defined coding function, with the exception of 32 nucleotides, of which 18 occur at the 5’ ends of open reading frames. Mouse mitochondrial DNA is unique in that the translational start codon is AUN, with any of the four nucleotides in the third position, whereas the only translational stop codon is the orthodox UAA. The mouse mitochondrial DNA genome is highly homologous in overall sequence and in gene organization to human mitochondrial DNA, with the descending order of conserved regions being tRNA genes; origin of light-strand replication; rRNA genes; known protein-coding genes; unidentified protein-coding genes; displacement-loop region.

Mycobacterium tuberculosis has a complex life cycle transitioning between active and dormant growth states depending on environmental conditions. LipN (Rv2970c) is a conserved mycobacterial serine hydrolase with regulated catalytic activity at the interface between active and dormant growth conditions. LipN also catalyzes the xenobiotic degradation of a tertiary ester substrate and contains multiple conserved motifs connected with the ability to catalyze the hydrolysis of difficult tertiary ester substrates. Herein, we expanded a library of fluorogenic ester substrates to include more tertiary and constrained esters and screened 33 fluorogenic substrates for activation by LipN, identifying its unique substrate signature. LipN preferred short, unbranched ester substrates, but had its second highest activity against a heteroaromatic five-membered oxazole ester. Oxazole esters are present in multiple mycobacterial serine hydrolase inhibitors but have not been tested widely as ester substrates. Combined structural modeling, kinetic measurements, and substitutional analysis of LipN showcased a fairly rigid binding pocket preorganized for catalysis of short ester substrates. Substitution of diverse amino acids across the binding pocket significantly impacted the folded stability and catalytic activity of LipN with two conserved motifs (HGGGW and GDSAG) playing interconnected, multidimensional roles in regulating its substrate specificity. Together this detailed substrate specificity profile of LipN illustrates the complex interplay between structure and function in mycobacterial hormone-sensitive lipase homologues and indicates oxazole esters as promising inhibitor and substrate scaffolds for mycobacterial hydrolases.

Recent work has highlighted that many types of variables are represented in each neocortical area. How can these many neural representations be organized together without interference, and coherently maintained/updated through time? We recorded from large neural populations in posterior cortices as mice performed a complex, dynamic task involving multiple interrelated variables. The neural encoding implied that correlated task variables were represented by uncorrelated modes in an information-coding subspace. We show via theory that this can enable optimal decoding directions to be insensitive to neural noise levels. Across posterior cortex, principles of efficient coding thus applied to task-specific information, with neural-population modes as the encoding unit. Remarkably, this encoding function was multiplexed with rapidly changing, sequential neural dynamics, yet reliably followed slow changes in task-variable correlations through time. We can explain this as due to a mathematical property of high-dimensional spaces that the brain might exploit as a temporal scaffold.

Voltage-gated CaV1.2 channels (L-type calcium channel α1C subunits) are critical mediators of transcription-dependent neural plasticity. Whether these channels signal via the influx of calcium ion (Ca2+), voltage-dependent conformational change (VΔC), or a combination of the two has thus far been equivocal. We fused CaV1.2 to a ligand-gated Ca2+-permeable channel, enabling independent control of localized Ca2+ and VΔC signals. This revealed an unexpected dual requirement: Ca2+ must first mobilize actin-bound Ca2+/calmodulin-dependent protein kinase II, freeing it for subsequent VΔC-mediated accumulation. Neither signal alone sufficed to activate transcription. Signal order was crucial: Efficiency peaked when Ca2+ preceded VΔC by 10 to 20 seconds. CaV1.2 VΔC synergistically augmented signaling by N-methyl-D-aspartate receptors. Furthermore, VΔC mistuning correlated with autistic symptoms in Timothy syndrome. Thus, nonionic VΔC signaling is vital to the function of CaV1.2 in synaptic and neuropsychiatric processes.