Parallel streams of raphe VGLUT3-positive inputs target the dorsal and ventral hippocampus in each hemisphere.

The hippocampus (HP) receives neurochemically diverse inputs from the raphe nuclei, including glutamatergic axons characterized by the expression of the vesicular glutamate transporter type 3 (VGLUT3). These raphe-HP VGLUT3 projections have been suggested to play a critical role in HP functions, yet a complete anatomical overview of raphe VGLUT3 projections to the forebrain, and in particular to the HP, is lacking. Using anterograde viral tracing, we describe largely nonoverlapping VGLUT3-positive projections from the dorsal raphe (DR) and median raphe (MnR) to the forebrain, with the HP receiving inputs from the MnR. A limited subset of forebrain regions such as the amygdaloid complex, claustrum, and hypothalamus receives projections from both the DR and MnR that remain largely segregated. This highly complementary anatomical pattern suggests contrasting roles for DR and MnR VGLUT3 neurons. To further analyze the topography of VGLUT3 raphe projections to the HP, we used retrograde tracing and found that HP-projecting VGLUT3-positive neurons (VGLUT3HP ) distribute over several raphe subregions (including the MnR, paramedian raphe, and B9 cell group) and lack co-expression of serotonergic markers. Strikingly, double retrograde tracing experiments unraveled two parallel streams of VGLUT3-positive projections targeting the dorsal and ventral poles of the HP. These results demonstrate highly organized and segregated VGLUT3-positive projections to the HP, suggesting independent modulation of HP functions such as spatial memory and emotion-related behavior.

Poly(3,4-ethylenedioxythiophene) (PEDOT) Coatings for High-Quality Electromyography Recording.

Conducting polymer coatings on metal electrodes are an efficient solution to improve neural signal recording and stimulation, due to their mixed electronic-ionic conduction and biocompatibility. To date, only a few studies have been reported on conducting polymer coatings on metallic wire electrodes for muscle signal recording. Chronic muscle signal recording of freely moving animals can be challenging to acquire with coated electrodes, due to muscle movement around the electrode that can increase instances of coating delamination and device failure. The poor adhesion of conducting polymers to some inorganic substrates and the possible degradation of their electrochemical properties after harsh treatments, such as sterilization, or during implantation limits their use for biomedical applications. Here, we demonstrate the mechanical and electrochemical stability of the conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT) doped with LiClO4, deposited on stainless steel multistranded wire electrodes for invasive muscle signal recording in mice. The mechanical and electrochemical stability was achieved by tuning the electropolymerization conditions. PEDOT-coated and bare stainless steel electrodes were implanted in the neck muscle of five mice for electromyographic (EMG) activity recording over a period of 6 weeks. The PEDOT coating improved the electrochemical properties of the stainless steel electrodes, lowering the impedance, resulting in an enhanced signal-to-noise ratio during in vivo EMG recording compared to bare electrodes.

Optogenetic Activation of Septal Glutamatergic Neurons Drive Hippocampal Theta Rhythms.

The medial septum and diagonal band of Broca (MS-DBB) has an essential role for theta rhythm generation in the hippocampus and is critical for learning and memory. The MS-DBB contains cholinergic, GABAergic, and recently described glutamatergic neurons, but their specific contribution to theta generation is poorly understood. Here, we examined the role of MS-DBB glutamatergic neurons in theta rhythm using optogenetic activation and electrophysiological recordings performed in in vitro preparations and in freely behaving mice. The experiments in slices suggest that MS-DBB glutamatergic neurons provide prominent excitatory inputs to a majority of local GABAergic and a minority of septal cholinergic neurons. In contrast, activation of MS-DBB glutamatergic fiber terminals in hippocampal slices elicited weak postsynaptic responses in hippocampal neurons. In the in vitro septo-hippocampal preparation, activation of MS-DBB glutamatergic neurons did increase the rhythmicity of hippocampal theta oscillations, whereas stimulation of septo-hippocampal glutamatergic fibers in the fornix did not have an effect. In freely behaving mice, activation of these neurons in the MS-DBB strongly synchronized hippocampal theta rhythms over a wide range of frequencies, whereas activation of their projections to the hippocampus through fornix stimulations had no effect on theta rhythms, suggesting that MS-DBB glutamatergic neurons played a role in theta generation through local modulation of septal neurons. Together, these results provide the first evidence that MS-DBB glutamatergic neurons modulate local septal circuits, which in turn contribute to theta rhythms in the hippocampus.

Parvalbumin Interneurons of Hippocampus Tune Population Activity at Theta Frequency.

Hippocampal theta rhythm arises from a combination of recently described intrinsic theta oscillators and inputs from multiple brain areas. Interneurons expressing the markers parvalbumin (PV) and somatostatin (SOM) are leading candidates to participate in intrinsic rhythm generation and principal cell (PC) coordination in distal CA1 and subiculum. We tested their involvement by optogenetically activating and silencing PV or SOM interneurons in an intact hippocampus preparation that preserves intrinsic connections and oscillates spontaneously at theta frequencies. Despite evidence suggesting that SOM interneurons are crucial for theta, optogenetic manipulation of these interneurons modestly influenced theta rhythm. However, SOM interneurons were able to strongly modulate temporoammonic inputs. In contrast, activation of PV interneurons powerfully controlled PC network and rhythm generation optimally at 8 Hz, while continuously silencing them disrupted theta. Our results thus demonstrate a pivotal role of PV but not SOM interneurons for PC synchronization and the emergence of intrinsic hippocampal theta.

Early alterations in hippocampal circuitry and theta rhythm generation in a mouse model of prenatal infection: implications for schizophrenia.

Post-mortem studies suggest that GABAergic neurotransmission is impaired in schizophrenia. However, it remains unclear if these changes occur early during development and how they impact overall network activity. To investigate this, we used a mouse model of prenatal infection with the viral mimic, polyriboinosinic-polyribocytidilic acid (poly I:C), a model based on epidemiological evidence that an immune challenge during pregnancy increases the prevalence of schizophrenia in the offspring. We found that prenatal infection reduced the density of parvalbumin- but not somatostatin-positive interneurons in the CA1 area of the hippocampus and strongly reduced the strength of inhibition early during postnatal development. Furthermore, using an intact hippocampal preparation in vitro, we found reduced theta oscillation generated in the CA1 area. Taken together, these results suggest that redistribution in excitatory and inhibitory transmission locally in the CA1 is associated with a significant alteration in network function. Furthermore, given the role of theta rhythm in memory, our results demonstrate how a risk factor for schizophrenia can affect network function early in development that could contribute to cognitive deficits observed later in the disease.

Small-conductance Cl- channels contribute to volume regulation and phagocytosis in microglia.

The shape and volume of microglia (brain immune cells) change when they activate during brain inflammation and become migratory and phagocytic. Swollen rat microglia express a large Cl(-) current (I(Clswell)), whose biophysical properties and functional roles are poorly understood and whose molecular identity is unknown. We constructed a fingerprint of useful biophysical properties for comparison with I(Clswell) in other cell types and with cloned Cl(-) channels. The microglial I(Clswell) was rapidly activated by cell swelling but not by voltage, and showed no time-dependence during voltage-clamp steps. Like I(Clswell) in many cell types, the halide selectivity sequence was I(-) > Br(-) > Cl(-) > F(-). However, it differed in lacking inactivation, even at +100 mV with high extracellular Mg(2+), and in having a much lower single-channel conductance: 1-3 pS. Based on these fundamental differences, the microglia channel is apparently a different gene product than the more common intermediate-conductance I(Clswell). Microglia express several candidate genes, with relative mRNA expression levels of: CLIC1 > ClC3 > I(Cln) > or = ClC2 > Best2 > Best1 > or = Best3 > Best4. Using a pharmacological toolbox, we show that all drugs that reduced the microglia current (NPPB, IAA-94, flufenamic acid and DIOA) increased the resting cell volume in isotonic solution and inhibited the regulatory volume decrease that followed cell swelling in hypotonic solution. Both channel blockers tested (NPPB and flufenamic acid) dose-dependently inhibited microglia phagocytosis of E. coli bacteria. Because I(Clswell) is involved in microglia functions that involve shape and volume changes, it is potentially important for controlling their ability to migrate to damage sites and phagocytose dead cells and debris.