The responsiveness of human eccrine sweat glands to choline and carbachol. Application to the study of peripheral cholinergic functioning in Alzheimer-type dementia

Expression of the high-affinity choline transporter, CHT1, in the neuronal and non-neuronal cholinergic system of human and rat skin

Choline is an essential component in acetylcholine biosynthesis, and is involved in cell signaling. It is unable to permeate the cell membrane and requires a transporter to enter the cell. Neurons that synthesize acetylcholine take up choline by a recently cloned high-affinity choline transporter (choline transporter 1) that is Na+-dependent and can be blocked by hemicholinium-3. The aim of this study was to determine the expression and to analyze the distribution of choline transporter 1 in human and rat skin. The mRNA for choline transporter 1 was detected in rat and human skin and in the human keratinocyte cell line HaCaT. A polyclonal anti-serum was developed against the N-terminal region of the human and rat protein. In rat and human skin, choline transporter 1 immunoreactivity was present in nerve fibers. In addition, keratinocytes, HaCaT cells and cells of the internal root sheath of the hair follicle contained choline transporter 1 immunoreactivity. The labeling patterns of nonconfluent vs confluent cultured cells and the distribution of choline transporter 1 along the epidermal layer suggest an association of choline transporter 1 with keratinocyte differentiation. In conclusion, this study shows the presence of the high-affinity choline transporter choline transporter 1 in nerve fibers and epithelial cells in the human and rat skin supporting the pivotal role of this transporter in both the neuronal and non-neuronal cholinergic system of the skin.

Altered pupillary size and darkness and light reflexes in Alzheimer's disease

The purpose was to compare resting pupil diameter in darkness and light, and the pupillary darkness and light reflexes between a group of patients with Alzheimer's disease and a group of healthy old people. Nine medication free patients with Alzheimer's disease and nine healthy control subjects, matched for sex and age with the patients, participated. There were six men and three women and the median age was 72 years in both groups. Pupil diameter was monitored with an infrared television pupillometer. Resting pupil diameter was smaller in the Alzheimer's disease group (P = 0.041, in darkness). The amplitude and the maximum dilatation velocity of the darkness reflex were smaller for the Alzheimer's disease group (maximum dilatation velocity P < 0.002). The amplitude and the 75% recovery time of the light reflex response were reduced in the Alzheimer's disease group (P < 0.002 and P = 0.034 respectively). There was no difference in the latency of the reflex response between the two groups. The reduced pupil size and diminished darkness reflex in the Alzheimer's disease group are consistent with a sympathetic deficit in the patients. The reduction in light reflex amplitude and recovery time are likely to be secondary to the grossly diminished pupil size in the patient group. The lack of any change in light reflex latency in the patients with Alzheimer's disease argues against an afferent defect. The pupillary changes in patients with Alzheimer's disease are qualitatively the same as those seen in healthy old people and are consistent with the notion of "accelerated aging" in Alzheimer's disease.

Muscarinic receptors on human eccrine sweat gland in aging and Alzheimer's disease

Age and Alzheimer's disease-related changes have been reported in the peripheral cholinergic system controlling sweating. We present (1) evidence of a high affinity muscarinic receptor localized on human eccrine sweat gland and (2) muscarinic receptor concentrations on eccrine gland samples from 22 patients with probable Alzheimer's disease of various degrees of dementia, 8 age-matched controls, and 11 young controls. Muscarinic receptors were measured using autoradiography with 3H-NMS as ligand. We found no evidence of changes related to aging or Alzheimer's disease in the overall concentration of receptors or in the amount of gland showing binding. Nor was there any correlation between the degree of dementia as measured by the Global Deterioration Scale or the Mini-Mental State Exam and 3H-NMS binding. In conclusion, we find no evidence that previously reported sweat gland functional changes associated with aging and Alzheimer's disease are reflected in changes in eccrine gland muscarinic receptor density.

Immunohistochemical, morphological and functional changes in the peripheral sudomotor neuro-effector system in elderly people

Age-related changes in the human peripheral sudomotor neuro-effector system have been investigated in six 80-year-olds and six young adults. Histochemical and immunohistochemical studies on forearm skin biopsies showed diminished vasoactive intestinal polypeptide (VIP) and calcitonin gene related peptide (CGRP)-like immunoreactivity and a virtual absence of acetylcholinesterase in the elderly sudomotor nerve endings compared to the young. Reduced size of nerve bundles and decreased density of sympathetic nerve endings adjacent to the sweat glands of old people were shown by the neuronal marker, protein gene product (PGP 9.5), and by electron microscopy. Image analysis techniques were also used to demonstrate a marked regression in secretory coil size with age. Functional decrements accompanying the neurochemical and morphological changes in the neuro-effector system were measured in ten 80-year-olds by local quantitative nicotine axon reflex responses and compared with 12 young adults. These studies demonstrate marked regressive changes in both the nerve endings and target cells in old age and appear to express a significant loss of vigour in trophic interactions.

In vivo studies on receptor pharmacology of the human eccrine sweat gland

The receptor pharmacology of the human sweat gland was studied in vivo. The axon-reflex response was mediated by nicotinic receptors which were activated by nicotine and acetylcholine, but not pilocarpine, and inhibited by hexamethonium. The direct response was mainly muscarinic, responding to pilocarpine and acetylcholine. A component of the direct response was nicotinic, since it was activated by nicotine and blocked by hexamethonium in a dose-dependent manner. The axon-reflex response to nicotine and acetylcholine was partially blocked by pilocarpine, especially when application of pilocarpine preceded the procedure. The inhibition of the nicotinic response may be secondary to M1 antagonism since pilocarpine is an M2 agonist and M1 antagonist and pirenzepine, a specific M1 antagonist, caused similar effects as pilocarpine.

The effect of diazepam on the responsiveness of human eccrine sweat glands to carbachol: influence of ambient temperature

The effect of diazepam (10 mg, p.o.) on the responsiveness of eccrine sweat glands to intradermally injected carbachol and on critical flicker fusion frequency was compared in 6 male healthy volunteers under two ambient temperature conditions, 22 degrees C and 35 degrees C. Carbachol evoked dose-related increases in sweat gland activity. Responsiveness to carbachol was significantly enhanced under the 35 degrees C condition as compared to the 22 degrees C condition, this being reflected in a higher value of Emax of the dose-response curve for carbachol under the 35 degrees C condition. Diazepam had no significant effect on responses to carbachol under the 22 degrees C condition, but prevented the increase in responsiveness produced by high ambient temperature. High ambient temperature had no significant effect on critical flicker fusion frequency. Diazepam significantly reduced critical flicker fusion frequency under both temperature conditions. It is suggested that diazepam may block the increase in sympathetic outflow normally evoked by high ambient temperature, thereby preventing the development of sweat gland hyper-responsiveness.

Effects of locally administered anticholinesterase agents on the secretory response of human eccrine sweat glands to acetylcholine and carbachol

The effects of locally administered physostigmine and di-isopropylphosphorofluoridate (DFP) were compared on the secretory response of sweat glands to intradermally injected acetylcholine and carbachol in healthy male volunteers (physostigmine: six subjects; DFP: one subject). The response to acetylcholine reached its peak within 10 s of injection and then rapidly declined, whereas the response to carbachol increased steadily reaching a peak between 5 and 7 min after injection. The response to acetylcholine was potentiated in the presence of both physostigmine and DFP, whilst the response to carbachol was not significantly affected by either of these drugs. The difference in the time-course of responses to acetylcholine and carbachol may be attributed to differences in the susceptibility of the two drugs to metabolism by acetylcholinesterase; carbachol, unlike acetylcholine, being virtually immune to metabolism by this enzyme. It is concluded that the response to carbachol is mediated by a direct stimulatory action on post-synaptic muscarinic receptors rather than by activation of pre-synaptic nicotinic receptors leading to the release of endogenous acetylcholine.

Effects of locally and systemically administered cholinoceptor antagonists on the secretory response of human eccrine sweat glands to carbachol

Eleven healthy male volunteers participated in a study comparing the effects of locally and systemically administered cholinoceptor antagonists on the secretory response of sweat glands to intradermally injected carbachol chloride. Atropine sulphate administered locally into the skin antagonised the response to carbachol: the dose-response curve for carbachol was shifted to the right without any depression of the maximum of the curve. The nicotinic receptor antagonists hexamethonium bromide and (+)-tubocurarine chloride, however, had little effect on the response to carbachol. Atropine sulphate, administered systemically by intramuscular injection, caused a non-surmountable antagonism of the response to carbachol: the maximum of the dose-response curve was depressed with little change in the value of ED50. Atropine methonitrate (a mixed muscarinic/nicotinic receptor antagonist), and hexamethonium bromide (a nicotinic receptor antagonist), both with poor access to the central nervous system, were injected intramuscularly: both caused non-surmountable antagonism of the response to carbachol. It is concluded that the response to carbachol is mediated by muscarinic rather than nicotinic receptors. The effect of atropine sulphate on the response to carbachol depends on the route of administration: while locally applied atropine sulphate appears to act as a competitive antagonist, systemically applied atropine sulphate, like atropine methonitrate and hexamethonium bromide, appears to act in a non-competitive manner. It is suggested that the systemically administered cholinoceptor antagonists reduce the response to carbachol by interacting with cholinoceptors in sympathetic ganglia: such an interaction would reduce the impulse flow in sudomotor fibres resulting in decreased sensitivity of the sweat glands to carbachol.

Hyper-responsiveness of eccrine sweat glands to carbachol in anxiety neurosis: comparison of male and female patients

The responsiveness of eccrine sweat glands to intradermally injected carbachol was studied in six male and six female healthy volunteers and six male and six female patients suffering from anxiety neurosis. Consistently greater responses to carbachol were obtained in the healthy males than in the healthy females. Analysis of the dose-response curves showed that this was reflected in a higher value of Emax in the males. Consistently greater responses to carbachol were obtained in the anxious males than in the healthy males, this being reflected in a higher value of Emax for the anxious subjects. Consistently greater responses to carbachol were obtained in the anxious females than in the healthy females, this being reflected in a higher value of Emax for the anxious subjects. In contrast to the results obtained with the healthy subjects, there was no sex-related difference in responsiveness to carbachol among the anxious patients. It is suggested that the hyper-responsiveness of sweat glands in anxiety states involves the sensitization of normally 'dormant' sweat glands by impulse flow in sudomotor sympathetic fibres. The upper limit to the value of Emax for carbachol, which may be determined by the number of potentially responsive glands, may be similar in the two sexes.

The effects of a psychological "stressor" and raised ambient temperature on the pharmacological responsiveness of human eccrine sweat glands: implications for sweat gland hyper-responsiveness in anxiety states

The responsiveness of eccrine sweat glands to local intradermal injections of carbachol was studied in six male healthy volunteers using a plastic paint impression method. A psychological "stressor" (performance of a mental arithmetic task) resulted in an increase in the sizes of the responses evoked by carbachol, this being reflected in a higher value of Emax obtained under the "stress" than under the "non-stress" condition. A rise in ambient temperature from 20 degrees C to 35 degrees C resulted in qualitatively similar effects on the dose-response curve. These results are discussed in the context of recent observations on the pharmacological responsiveness of sweat glands in patients suffering from anxiety neurosis.