The central nervous control of walking in the locust, Schistocerca Americana

Rhythmic motor behaviors in all animals appear to be under the control of "central pattern generator" circuits, neural circuits which can produce output patterns appropriate for behavior even when isolated from their normal peripheral inputs. Insects have been a useful model system in which to study the control of legged terrestrial locomotion. Much is known about walking in insects at the behavioral level, but to date there has been no clear demonstration that a central pattern generator for walking exists. The focus of this thesis is to explore the central neural basis for locomotion in the locust, Schistocerca americana.

Rhythmic motor patterns could be evoked in leg motor neurons of isolated thoracic ganglia of locusts by the muscarinic agonist pilocarpine. These motor patterns would be appropriate for the movement of single legs during walking. Rhythmic patterns could be evoked in all three thoracic ganglia, but the segmental rhythms differed in their sensitivities to pilocarpine, their frequencies, and the phase relationships of motor neuron antagonists. These different patterns could be generated by a simple adaptable model circuit, which was both simulated and implemented in VLSI hardware. The intersegmental coordination of leg motor rhythms was then examined in preparations of isolated chains of thoracic ganglia. Correlations between motor patterns in different thoracic ganglia indicated that central coupling between segmental pattern generators is likely to contribute to the coordination of the legs during walking.

The work described here clearly demonstrates that segmental pattern generators for walking exist in insects. The pattern generators produce motor outputs which are likely to contribute to the coordination of the joints of a limb, as well as the coordination of different limbs. These studies lay the groundwork for further studies to determine the relative contributions of central and sensory neural mechanisms to terrestrial walking.

Synthesis and characterization of 1,1-di-tert-butyldiazene

The synthesis and direct observation of 1,1-di-tert-butyldiazene (16) at -127°C is described. The absorption spectrum of a red solution of 1,1-diazene 16 reveals a structured absorption band with λ max at 506 run (Me_2O, -125°C). The vibrational spacing in S_1 is about 1200 cm^(-1). The excited state of 16 emits weakly with a single maximum at 715 run observed in the fluorescence spectrum (Me_2O:CD_2Cl_2, -196°C). The proton NMR spectrum of 16 occurs as a singlet at 1.41 ppm. Monitoring this NMR absorption at -94^0 ± 2°C shows that 1,1-diazene 16 decomposes with a first-order rate of 1.8 x 10^(-3) sec(-1) to form isobutane, isobutylene and hexarnethylethane. This rate is 10^8 and 10^(34) times faster than the thermal decomposition of the corresponding cis and trans 1,2-di-tert-butyldiazene isomers. The free energy of activation for decomposition of 1,1-diazene 16 is found to be 12.5 ± 0.2 kcal/mol at -94°C which is much lower than the values of 19.1 and 19.4 kcal/lmole calculated at -94°C for N-(2,2,6,6- tetramethylpiperidyl)nitrene (3) and N-(2,2,5,5- tetrarnethylpyrrolidyl)nitrene (4), respectively. This difference between 16 and the cyclic-1,1-diazenes 3 and 4 can be attributed to a large steric interaction between the tert-butyl groups in 1,1-diazene 16.

In order to investigate the nature of the singlet-triplet gap in 1,1-diazenes, 2,5-di-tert-butyl-N-pyrrolynitrene (22) was generated but was found to be too reactive towards dimerization to be persistent. In the presence of dimethylsulfoxide, however, N-pyrrolynitrene (22) can be trapped as N-(2,5-di-tert-butyl- N'-pyrrolyl)dimethylsulfoxirnine (38). N-(2,5-di-tert-butyl-N'-pyrrolyl)dimethylsulfoximine (38-d^6) exchanges with free dimethylsulfoxide at 50°C in solution, presumably by generation and retrapping of pyrrolynitrene 22.

Industrial democracy

Since the beginning of human relations, some of the more ambitious and more capable members of society have by various means found and practiced methods of exploiting the efforts of their fellowmen to their own personal interest. These individuals have been naturally gifted at organization and control and have been able to dominate their slower, less mentally active associates. It is a cumulative process, once having been started the act of further subjugation becoming easier and easier as the clever person gets more and more control over the other.

I. The effect of N,N,N',N' -tetramethylethylenediamine on the Schlenk Equilibrium. II. The nature of the Di-Grignard reagent

I. The influence of N,N,N’,N’-tetramethylethylenediamine on the Schlenk equilibrium

The equilibrium between ethylmagnesium bromide, diethylmagnesium, and magnesium bromide has been studied by nuclear magnetic resonance spectroscopy. The interconversion of the species is very fast on the nmr time scale, and only an averaged spectrum is observed for the ethyl species. When N,N,N’,N’-tetramethylethylenediamine is added to solutions of these reagents in tetrahydrofuran, the rate of interconversion is reduced. At temperatures near -50°, two ethylmagnesium species have been observed. These are attributed to the different ethyl groups in ethylmagnesium bromide and diethylmagnesium, two of the species involved in the Schlenk equilibrium of Grignard reagents.

II. The nature of di-Grignard reagents

Di-Grignard reagents have been examined by nuclear magnetic resonance spectroscopy in an attempt to prove that dialkylmagnesium reagents are in equilibrium with alkylmagnesium halides. The di-Grignard reagents of compounds such as 1,4-dibromobutane have been investigated. The dialkylmagnesium form of this di-Grignard reagent can exist as an intramolecular cyclic species, tetramethylene-magnesium. This cyclic form would give an nmr spectrum different from that of the classical alkylmagnesium halide di-Grignard reagent. In dimethyl ether-tetrahydrofuran solutions of di-Grignard reagents containing N N,N,N’,N’-Tetramethylethylenediamine, evidence has been found for the existence of an intramolecular dialkylmagnesium species. This species is rapidly equilibrating with other forms, but at low temperatures, the rates of interconversion are reduced. Two species can be seen in the nmr spectrum at -50°. One is the cyclic species; the other is an open form.

Inversion of the carbon at the carbon-magnesium bond in di-Grignard reagents has also been studied. This process is much faster than in corresponding monofunctional Grignard reagents.