Nonsomatotopic Organization of the Higher Motor Centers in Octopus

Hyperredundant limbs with a virtually unlimited number of degrees of freedom (DOFs) pose a challenge for both biological and computational systems of motor control. In the flexible arms of the octopus, simplification strategies have evolved to reduce the number of controlled DOFs [1], [2] and [3]. Motor control in the octopus nervous system is hierarchically organized [4] and [5]. A relatively small central brain integrates a huge amount of visual and tactile information from the large optic lobes and the peripheral nervous system of the arms [6], [7], [8] and [9] and issues commands to lower motor centers controlling the elaborated neuromuscular system of the arms. This unique organization raises new questions on the organization of the octopus brain and whether and how it represents the rich movement repertoire. We developed a method of brain microstimulation in freely behaving animals and stimulated the higher motor centers—the basal lobes—thus inducing discrete and complex sets of movements. As stimulation strength increased, complex movements were recruited from basic components shared by different types of movement. We found no stimulation site where movements of a single arm or body part could be elicited. Discrete and complex components have no central topographical organization but are distributed over wide regions.     

A hitherto unknown transketolase-catalyzed reaction

Yeast transketolase, in addition to catalyzing the transferase reaction through utilization of two substrates--the donor substrate (ketose) and the acceptor substrate (aldose)--is also able to catalyze a one-substrate reaction with only aldose (glycolaldehyde) as substrate. The interaction of glycolaldehyde with holotransketolase results in formation of the transketolase reaction intermediate, dihydroxyethyl-thiamin diphosphate. Then the glycolaldehyde residue is transferred from dihydroxyethyl-thiamin diphosphate to free glycolaldehyde. As a result, the one-substrate transketolase reaction product, erythrulose, is formed. The specific activity of transketolase was found to be 0.23 U/mg and the apparent Km for glycolaldehyde was estimated as 140 mM.     

Vincamine: A psychogeriatric agent blocking synaptic potentiation in hippocampus

The action of vincamine on the physiology of the CAl region of the in vitro hippocampal slice preparation was investigated. At concentrations of 1, 10 and 100 μM, a five-minute perfusion with vincamine did not affect the synaptically-mediated activation of pyramidal neurons evoked by stimulation of the Schaffer-commissural fiber system. The effect of vincamine on the excitability of the pyramidal neurons was investigated by studying its effect on the antidromically-elicited field potential and the input-output relation of Schaffer-commissural fiber input. No effect on either of the two parameters was seen at a concentration of 100 μM of vincamine.Vincamine did, however, attenuate both the post-tetanic (PTP) and long-term potentiation (LTP) evoked by repetitive stimulation of the Schaffer-commissural fiber system. At a concentration of 100 μM of vincamine, PTP was significantly reduced and LTP was almost completely suppressed.     

On the stability of a model of testosterone dynamics

We prove the global asymptotic stability of a well-known delayed negative-feedback model of testosterone dynamics, which has been proposed as a model of oscillatory behavior. We establish stability (and hence the impossibility of oscillations) even in the presence of delays of arbitrary length.Supported in part by AFOSR Grant F49620-01-1-0063, NIH Grant P20 GM64375, and Dimacs.E.D. Sontag: Supported in part by AFOSR Grant F49620-01-1-0063 and NIH Grant R01 GM46383.Acknowledgement We would like to thank Augusto Ponce for useful suggestions.     

Immunohistochemical detection of [corrected] TrkB in the enteric nervous system of the small intestine in pigeon (Columba livia)

The presence and cell localization of TrkB, the main receptor for the neurotrophins (NTs), was investigated immunohistochemically in the small intestine of adult pigeons, with special reference to the enteric nervous system (ENS). Several neuronal (neurofilament proteins and PGP 9.5) and glial cell (S100 protein) markers were studied in parallel. TrkB immunoreactivity (TrkB-IR) was found to be restricted to immunohistochemically-identified glial cells present in the enteric plexuses, and to Schwann cells forming the perivascular plexus. Also, TrkB-IR was detected in enterochromaffin cells and in unidentified dendritic cells within the gut-associated lymphoid tissue. The present results demonstrate that as for mammals, TrkB in the ENS is restricted to the glial cells. The possible function of the TrkB ligands, however, remains to be established.     

Centrin: its secondary structure in the presence and absence of cations

Centrin is a low molecular mass (20 kDa) protein that belongs to the EF-hand superfamily of calcium-binding proteins. Local and overall changes were investigated for interactions between cations and Chlamydomonas centrin using Fourier transform infrared (FT-IR) and circular dichroic (CD) spectroscopies. FT-IR spectral features studied included the amide I' band and the side-chain absorbances for aspartate residues located almost exclusively at the calcium-binding sites in the spectral region of 1700-1500 cm(-1). The amide I' band is exquisitely sensitive to changes in protein secondary structure and is observed to shift from 1626.5 to 1642.7 cm(-1) in the presence and absence of calcium. These spectral bands are complex and were further studied using two-dimensional Fourier transform infrared (2D-FT-IR) correlation along with curve-fitting routines. Using these methods the secondary structure contributions were determined for holocentrin and apocentrin. The alpha-helical content in centrin was determined to be 60%-53% in the presence and absence of cations, respectively. Furthermore, the beta-strand content was determined to be 12%-36%, while the random coil component remained almost constant at 7%-13.5% in the presence and absence of cations, respectively. Changes in the side-chain band are mostly due to the monodentate coordination of aspartate to the cation. A shift of approximately 4 cm(-1) (for the COO- antisymmetric stretch in Asp) from 1565 to 1569 cm(-1) is observed for apocentrin and holocentrin, respectively. Thermal dependence revealed reversible conformational transition temperatures for apocentrin at 37 degrees C and holocentrin at 45 degrees C, suggesting greater stability for holocentrin.     

How to move with no rigid skeleton? The octopus has the answers

The octopus is amazingly flexible and shows exceptional control and coordination in all its movements. It seems remarkable to us skeletal creatures that the octopus achieves all this without a single bone.