Most of the animals know seasons via environmental signals and adapt the development and reproduction to cyclic seasonal changes. Among those, length of a day (photoperiod) is the most reliable because of constancy through years, and thus many animals use photoperiod as a seasonal cue. The physiological response of organisms to photoperiod is called photoperiodism. The blow fly, Protophormia terraenovae has relatively large body size of 1cm length, and live in high-latitude regions such as Hokkaido or Aomori prefecture in Japan. Females of the blow fly have adult diapause induced under the short-day and low-temperature conditions in autumn. It is believed that the diapausing flies overwinter, for instances, among stacked fallen leaves beneath snow. Overwintered flies mate and lay eggs from spring to early summer. Now we have accumulated data about photoperiodic photoreceptors (photoreceptors in the compound eye), an endocrine organ (corpus allatum), and brain neurosecretory cells (PI neurons and PL neurons) regulating diapause induction and reproduction in P. terraenovae. Furthermore, it has been demonstrated that circadian clock neurons (small ventral lateral neuron, s-LN_v) driving circadian rhythm are involved in photoperiodism in this species, and that LN_v including s-LN_v synapses upon PL neurons crucial for diapause induction. Besides, both the expression pattern of a circadian clock gene (period) in the brain and subcellular localization of PERIOD in LN_v alter in a photoperiod-dependent manner. Light information received in the compound eyes is probably translated into photoperiodic information, such as long days or short days in LN_v. It seems that PL neurons receiving the short-day information from LN_v change own electrophysiological properties to induce diapause. In this review, I introduce neural bases underlying photoperiodism of insects, focusing on the knowledge revealed in a non-model organism, P. terraenovae.

Females of social Hymenoptera mate only at the beginning of their adult lives and produce offspring until their death without additional mating. In most ant species, queens live for over a decade, indicating that ant queens can store large numbers of spermatozoa throughout their long lives. Because morphology of the spermatheca (sperm storage organ) in ant queens is very unique among social Hymenoptera, this organ should be important for long-term sperm storage mechanisms in ants. Sperm cells are immotile in the spermatheca of queens at 5 years after mating. This may be effective to maintain a low metabolic activity of spermatozoa that prevents cellular damage and inhibits reactive oxygen species production. The immotile spermatozoa begin to swim when they are exposed to PBS buffer. This indicates that spermatozoa do not lack flagellum functions and continue to survive even after storage for 5 years. Sperm morphology of ants is similar to that of other hymenopteran species, however differences of the cellular characterization is still unknown (e.g. tolerance to oxidative stress) . Highly expressed genes in the ant spermatheca relative to those in body samples have been identified. The genes identified include those encoding antioxidant enzymes, chaperones, and energy metabolism enzymes as well as novel genes that have no similar sequences in the public databases. In future study, it should be necessary to identify the genes responsible for the sperm longevity in ant queens and shed light on molecular and cellular mechanisms of the long-term sperm storage.

Visual search is the first step for humans’ shopping and animals’ foraging. “Object skill” is an important skill for quickly detecting a valuable object and deciding to accept or reject it. Rhesus monkeys (Macaca Mulatta) show remarkable performance for quickly finding a “good object” among many objects after repetitive object-reward association learning. Monkeys can discriminate many good objects from many bad objects (〜300 objects) for long time after learning (more than 100 days). What neuronal circuits enable animals to retain this high-capacity and long-term memory for finding valuable objects? Our previous and current studies indicate that the basal ganglia circuits are involved in detecting good or bad objects and making saccade to good objects based on this memory. Our optogenetic and neuropharmacological experiments demonstrated that two parallel circuits in the basal ganglia work in a coordinated manner for the object skill. Direct pathway in the basal ganglia, which is activated by presentation of good objects, facilitates saccade to good objects. Indirect pathway, which is activated by presentation of bad objects, suppressed saccade to bad objects. Not only accepting good objects but also rejecting bad objects is critical for finding and selecting a valuable object among many objects.

In this note, we introduce comprehensive voltage-sensitive dye (VSD) imaging using a double-sided microscope. We performed this imaging technique on the nervous system of the medicinal leech (Hirudo verbana). In the leech segmental ganglion, there are two neuronal layers: ventral and dorsal surfaces, where cell bodies of approximately 400 neurons, including sensory, motor, and interneurons, distribute. We applied a new generation VSD (VoltageFluor) to both ventral and dorsal surfaces of the ganglion to achieve simultaneous VSD imaging in a whole ganglion. We could detect both small synaptic potentials and action potentials in imaged neurons with a high S/N ratio. Future issues are to develop long-time imaging in a low photo-bleaching condition and its application to semi-intact leech preparations.