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Trans-synaptic regulation of the growth and development of adrenergic neurons
viii
Frontiers in Catecholamine Reae~ch
TRANS-SYNAPTIC REGULATION OF THE GROWTH AND DEVELOPMENT OF ADRENERGIC NEURONS Ira B. Black Dept . of Neurology, Cornell Univ. School oP Medicine, New York 10021, U.S .A . The trophic effects of nerve on muscle have been well-documented. However little is known about the trophic influences of one nerve on another neuron. The superior cervical ganglion (SCG) in the developing mouse was employed as a model system to investigate not only neuronal growth and development, but also inter neural communication and neuronal plasticity . Choline acetyltransferase (ChAc), the enzyme catalyzing the conversion of acetyl-Co-A and choline to acetylcholine, served as a marker for the development of pre-synaptic cholinergic fibers in the ganglion . This enzyme is highly localized to these pre-synaptic terminals. Maturation of post-synaptic neurons was followed by measuring the activity of tyrosine hydroxylase (T-OH), the rate-limiting enzyme in the biosynthesis of norepinephrine, the post-gang ionic neurotransmitter . During the course of development ChAc activity increases over a forty to fifty-fold range; describing a hyperbolic curve, and approximating adult levels at three weeks of age. T-OH activity, on the other hand, increases six to eight fold during ontogeny~r and reaches adult levels at two weeks of age. Considerable evidence suggests that this increase is due to de novo enzyme protein synthesis. During the, same period of time total ganglion proteia gradually rises to two to three-fold, rendering the changes in specific enzyme activities highly significant . Estimation of synapse numbers electron microscopically in ganglia from mice of different ages permitted correlation of the biochemistry and morphology of maturation . Ganglion synapses increase markedly during the post-natal period, from approximately 8,000 on day 1 of life to 3,000,000 during adulthood. The developmental curve of ChAc activity is virtually congruent with that of synapse numbers, suggesting that increased enzyme activity reflects the formation of synaptic connections. On the other hand, the major increase in T-OH activity parallels the marked, rise in synapse numbers, suggesting that the formation of synaptic contacts may be necessary for maturation of T-OH activity . This hypothesis may be investigated by unilaterally decentralizing ganglia in neonatal mice . Surgical transaction of the preganglionic nerve trunk prevents the normal development of T-OH activity in post-synaptic adrenergic neurons, enzyme activity remaining depressed for at least three months after surgery. These observations suggest that presynaptic nerve terminals regulate the biochemical maturation of postsynaptic adrenergic neurons in SCG. Efforts to identify the trans-synaptic messages) focussed on Nerve Grdwth Factor (NGF) and acetylcholine itself . Ganglia were unilaterally decentralized in neonatal mice, and one group of animals was treated with saline while another
Frontiers in Catecholamine Research
ix
was treated with Nerve Growth Factor . NGF administration results in a marked increase in T-OH activity in intact ganglia reflecting the growth response of adrenergic neurons. Decentralization markedly inhibits the response to NGF. However, even in decentralized ganglia, NGF treatment results in a small but significant increase in T-OH activity . On the basis of these observations it would appear that NGF cannot entirely replace presynaptic terminals during maturation and therefore that NGF cannot represent the sole traassynaptic message involved in the regulation of T-OH development. The traps-synaptic role of acetylcholine was investigated by treating neonatal mice with the ganglion-blocking agents chlorisondamine or pempidine . These compounds prevent depolarization of post-synaptic neurons in sympathetic ganglia by competing with acetylcholine for receptor sites. Treatment with these agents prevents the normal development of T-OH activity in post-synaptic neurons of the SCG, reproducing the effect of ganglion decentralization . These observations suggest that acetycholine-induced depolarization of post-synaptic neurons is necessary for the normal development of T-OH activity in these cells. Consequently, it may not be necessary to postulate the existence of some es yet unidentified traps-synaptic trophic factors, since the normal pre-synaptic transmitter may also regulate the maturation of adrenergic neurons. In addition to the anterograde traps-synaptic regulation discussed above, post-synaptic neurons exert retrograde influences on the development of pre-synaptiç nerves in SCG. Treatment of neonatal mice with 6-hydroxydopamine (6-0HDA) or anti-Nerve Growth Factor Antiserum (anti-NGF), substances which selectively destroy ganglionic adrenergic neurons, prevents the normal maturation of pre-synaptic ChAc activity . These findings suggest that destruction of postsynaptic neurons prevents the normal maturation of pre-synaptic nerves in SCG. These results in conjunction with the previous observations suggest that a reciprocal regulatory relationship exists between the pre- and post-synaptic neurons in developing mouse autonomic ganglia. NOREPINEPHRIIVE AS A CENTRAL SYNAPTIC TRANSMITTER F . E. Bloom snd B. J . Hoffer Lab. oP Neurophermacology, N1MH, St. Elizabeths Hospital, Washington D . C . 20032, U .S .A .
Recent advances in the analysis of synaptic functional roles mediated by norepinephrine within the central nervous system can be divided into categories consisting of consecutive phases of electrophysiological and pharmacological research . At the most superficial level of analysis are additional studies on the effects of iontophoretically applied norepinephrine, or catecholamine synergists and antagonists, on the discharge rates end patterns of spontaneously active or amino acid-activated neurons in various portions of the brain. The predominant
Frontiers in Catecholamine Reae~ch
TRANS-SYNAPTIC REGULATION OF THE GROWTH AND DEVELOPMENT OF ADRENERGIC NEURONS Ira B. Black Dept . of Neurology, Cornell Univ. School oP Medicine, New York 10021, U.S .A . The trophic effects of nerve on muscle have been well-documented. However little is known about the trophic influences of one nerve on another neuron. The superior cervical ganglion (SCG) in the developing mouse was employed as a model system to investigate not only neuronal growth and development, but also inter neural communication and neuronal plasticity . Choline acetyltransferase (ChAc), the enzyme catalyzing the conversion of acetyl-Co-A and choline to acetylcholine, served as a marker for the development of pre-synaptic cholinergic fibers in the ganglion . This enzyme is highly localized to these pre-synaptic terminals. Maturation of post-synaptic neurons was followed by measuring the activity of tyrosine hydroxylase (T-OH), the rate-limiting enzyme in the biosynthesis of norepinephrine, the post-gang ionic neurotransmitter . During the course of development ChAc activity increases over a forty to fifty-fold range; describing a hyperbolic curve, and approximating adult levels at three weeks of age. T-OH activity, on the other hand, increases six to eight fold during ontogeny~r and reaches adult levels at two weeks of age. Considerable evidence suggests that this increase is due to de novo enzyme protein synthesis. During the, same period of time total ganglion proteia gradually rises to two to three-fold, rendering the changes in specific enzyme activities highly significant . Estimation of synapse numbers electron microscopically in ganglia from mice of different ages permitted correlation of the biochemistry and morphology of maturation . Ganglion synapses increase markedly during the post-natal period, from approximately 8,000 on day 1 of life to 3,000,000 during adulthood. The developmental curve of ChAc activity is virtually congruent with that of synapse numbers, suggesting that increased enzyme activity reflects the formation of synaptic connections. On the other hand, the major increase in T-OH activity parallels the marked, rise in synapse numbers, suggesting that the formation of synaptic contacts may be necessary for maturation of T-OH activity . This hypothesis may be investigated by unilaterally decentralizing ganglia in neonatal mice . Surgical transaction of the preganglionic nerve trunk prevents the normal development of T-OH activity in post-synaptic adrenergic neurons, enzyme activity remaining depressed for at least three months after surgery. These observations suggest that presynaptic nerve terminals regulate the biochemical maturation of postsynaptic adrenergic neurons in SCG. Efforts to identify the trans-synaptic messages) focussed on Nerve Grdwth Factor (NGF) and acetylcholine itself . Ganglia were unilaterally decentralized in neonatal mice, and one group of animals was treated with saline while another
Frontiers in Catecholamine Research
ix
was treated with Nerve Growth Factor . NGF administration results in a marked increase in T-OH activity in intact ganglia reflecting the growth response of adrenergic neurons. Decentralization markedly inhibits the response to NGF. However, even in decentralized ganglia, NGF treatment results in a small but significant increase in T-OH activity . On the basis of these observations it would appear that NGF cannot entirely replace presynaptic terminals during maturation and therefore that NGF cannot represent the sole traassynaptic message involved in the regulation of T-OH development. The traps-synaptic role of acetylcholine was investigated by treating neonatal mice with the ganglion-blocking agents chlorisondamine or pempidine . These compounds prevent depolarization of post-synaptic neurons in sympathetic ganglia by competing with acetylcholine for receptor sites. Treatment with these agents prevents the normal development of T-OH activity in post-synaptic neurons of the SCG, reproducing the effect of ganglion decentralization . These observations suggest that acetycholine-induced depolarization of post-synaptic neurons is necessary for the normal development of T-OH activity in these cells. Consequently, it may not be necessary to postulate the existence of some es yet unidentified traps-synaptic trophic factors, since the normal pre-synaptic transmitter may also regulate the maturation of adrenergic neurons. In addition to the anterograde traps-synaptic regulation discussed above, post-synaptic neurons exert retrograde influences on the development of pre-synaptiç nerves in SCG. Treatment of neonatal mice with 6-hydroxydopamine (6-0HDA) or anti-Nerve Growth Factor Antiserum (anti-NGF), substances which selectively destroy ganglionic adrenergic neurons, prevents the normal maturation of pre-synaptic ChAc activity . These findings suggest that destruction of postsynaptic neurons prevents the normal maturation of pre-synaptic nerves in SCG. These results in conjunction with the previous observations suggest that a reciprocal regulatory relationship exists between the pre- and post-synaptic neurons in developing mouse autonomic ganglia. NOREPINEPHRIIVE AS A CENTRAL SYNAPTIC TRANSMITTER F . E. Bloom snd B. J . Hoffer Lab. oP Neurophermacology, N1MH, St. Elizabeths Hospital, Washington D . C . 20032, U .S .A .
Recent advances in the analysis of synaptic functional roles mediated by norepinephrine within the central nervous system can be divided into categories consisting of consecutive phases of electrophysiological and pharmacological research . At the most superficial level of analysis are additional studies on the effects of iontophoretically applied norepinephrine, or catecholamine synergists and antagonists, on the discharge rates end patterns of spontaneously active or amino acid-activated neurons in various portions of the brain. The predominant