Studies of sympathetic nerve activity in cutaneous nerves in healthy subjects using intraneural microneurography : The relationship between nerve activity and effector organ response

Sammanfattning: The aim of the research presented in this thesis is to gain new knowledge of the characteristic features of sympathetic nerve activity of cutaneous nerves in healthy adult humans using intraneural microneurography. One further goal is to study the relationship between nerve activity and effector organ response.The study has three main aims: I) to study temperature regulating mechanisms in human subjects, rhythm generating mechanism of nerve activity and the relationship between nerve activity and effector organs, including sweat glands and blood vessels, II) to study regional similarities and differences in sympathetic nerve activity recorded from different cutaneous nerves, III) to study effector organ response, without central nervous system influences, through intraneural stimulation after proximal nerve blocking.The most important results are as follows: 1) By exposing a human subject to warm and cold environments, it is possible to obtain selective activation of either the sudomotor or vasoconstrictor neural system. 2) Bursts of both sudomotor and vasoconstrictor activity occur at certain intervals and several types of rhythmic activity can be observed. 3) Sudomotor bursts have a shorter duration compared to vasoconstrictor bursts. 4) The rhythm generating mechanisms may help to restrict the firing rates of individual nerve fibres to low ranges, which provides high gain in the neuroeffector transfer function. 5) Simultaneous double nerve recordings provide evidence that in the distal glabrous skin area the thermoregulatory functions are mainly executed via vasoconstrictor nerve fibres. Instead, sudomotor fibres are brought into action only at relatively high temperatures. In the hairy skin of forearm and hand reflex thermoregulation is to large extent executed via sudomotor nerve fibres. 6) Intraneural electrical stimulation of sympathetic postganglionic axons in human skin nerves after proximal nerve blocking shows differences between sudomotor and vasoconstrictor effector organ responses.These results improve our knowledge of the function of the sympathetic nervous system in healthy human subjects.