Motor centers

Axons of antennal ORCs project through the antennal nerve to enter the brain at the level of the ipsilateral antennal lobe (AL) of the deutocerebrum (52). ORC axons project from the flagellum to targets in the AL, but axons from antennal mechanosensory neurons bypass the AL and project instead to an "antennal mechanosensory and motor center" in the deutocerebrum posteroventral (with respect to the body axis of the animal) to the AL (52, 58, 64). In moths and certain other insect groups, sex-pheromonal information is processed in a prominent male-specific neuropil structure in each AL called the macroglomerular complex (MGC) (16, 52, 64, 65). 

Phenobarbital noticeably reduces the excitation of motor centers of the brain, and therefore is used in treating both minor and major epileptic attacks, chorea, and spastic paralysis. Luminal, adonal, seconal, and many others are synonyms for this drug. 

In the normal state, the putamen receives afferents from the motor and somatosensory cortical areas and communicates with the GPi/SNr through a direct inhibitory pathway and though a multisynaptic (GPe, STN) indirect pathway. In PD, dopamine deficiency leads to increased inhibitory activity from the putamen onto the GPe and disinhibition of the STN. STN hyperactivity by virtue of its gluta-matergic action produces excessive excitation of the GPi/SNr neurons, which overinhibit the thalamocortical and brain stem motor centers. 

Barbiturates depress neuronal activity in the CNS. This is accompanied by decreased cerebral metabolic oxygen consumption and decreased cerebral blood flow, since the coupling of blood flow to brain metabolism is preserved with the barbiturates. It also results in a decrease in ICP. Barbiturates depress neuronal activity in the cerebral cortex, thalamus and motor centers. Barbiturates are effective anticonvulsants (see Ch. 9), reduce intraocular pressure, increase the threshold of spinal reflexes and provide excellent muscle relaxation. The barbiturates lack specific analgesic effects and are, therefore, not suitable as the sole anesthetic for invasive procedures. 

The expression of GP5 is limited to brain and retina (Watson et al., 1994, 1996). We recently completed an analysis of GP5 expression in mouse brain using in situ hybridization (Zhang et al., manuscript submitted). Besides it presence in motor centers such as forebrain motor cortex, the analysis revealed prominent expression of GPj in several afferent and sensory neural systems. The latter included multiple rhinencephalic structures the olfactory bulb, accessory olfactory nucleus, piriform and entorhinal cortex, septal nuclei, indusium griseum, mammillary nuclei... 

The matching dichotomy of sensilla construction and neuroanatomical organization of sensory neuropils suggests that in crustaceans chemical information is received and processed in two fundamentally different modes. One mode is Olfaction which we define as chemoreception mediated by the aesthetasc - OL pathway the second mode is Distributed Chemoreception, which we define as chemoreception mediated by bimodal sensilla on all appendages and the associated striated neuropils that serve as local motor centers. Distributed chemoreception not only comprises taste, which we define as contact chemoreception in the context of... 

Separate but concurrent research efforts by many investigators in basic neurophysiology were making significant advancements in developing an understanding of how cortical and spinal neural systems control motor function. Extensive research on control of movement by hundreds of neuroscientists has revealed correlations between parameters of limb movement and neural activity in many motor centers, including the primary motor cortex, premotor and supplementary motor cortex, cerebellum, and spinal cord. 

A considerable number of natural products are derived from indole. Very important is the essential amino acid tryptophan (133), a constituent of many proteins. Enzymatic conversion of tryptophan in living organisms produces additional natural products, for example, serotonin (134, 5-hydroxytryptamine) by hydroxylation and decarboxylation. It occurs in the semm of warm-blooded animals as a vasoconstrictor, and is one of the agents responsible for maintaining vascular tone. Moreover, it acts as a neurotransmitter, that is, it is essential for conducting impulses between nerve cells. Bufotenin (135), a poison occurring in the skin of toads, causes a rise in blood pressure and paralyzes the spinal and cerebral motor centers. Psilocin (136), the psychoactive substance in the Mexican mushroom Teonanacatl, increases excitability and causes hallucinations. 

The evidence discussed above indicates that amphioxus has divisions (1) a diencephalic forebrain with perhaps an anterior midbrain, but without a telencephalon and (3) the posterior hindbrain and spinal cord (or rhombospinal region), but have left open the question of whether the amphioxus nerve cord includes a region comparable to the vertebrate MHB. Posterior to the proposed tectum, Lacalli s (1996) anatomical studies revealed a number of ventral motor neurons and interneurons, which he termed the primary motor center . In vertebrates, motor nuclei occur in the MHB region and also throughout the hindbrain. Lacalli (1996) considers the posterior part of the primary motor center to be a hindbrain structure lying perhaps at the level of the rhombomere 2 equivalent, and points out that if this is true, then there would be very little space left between there and the tectum for either rhombomere 1 or the MHB . 

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