Gastric dysregulation induced by microinjection of 6-OHDA in the substantia nigra pars compacta of rats is determined by alterations in the brain-gut axis

Abstract

Toti L, Travagli RA. Gastric dysregulation induced by microinjection of 6-OHDA in the substantia nigra pars compacta of rats is determined by alterations in the brain-gut axis. Am J Physiol Gastrointest Liver Physiol 307: G1013-G1023, 2014. First published October 2, 2014; doi:10.1152/ajpgi.00258.2014.-Idiopathic Parkinson's disease (PD) is a late-onset, chronic, and progressive motor dysfunction attributable to loss of nigrostriatal dopamine neurons. Patients with PD experience significant gastrointestinal (GI) issues, including gastroparesis. We aimed to evaluate whether 6-hydroxy-dopamine (6-OHDA)-induced degeneration of dopaminergic neurons in the substantia nigra pars compacta (SNpc) induces gastric dysmotility via dysfunctions of the brain-gut axis. 6-OHDA microinjection into the SNpc induced a Ͼ90% decrease in tyrosine hydroxylase-immunoreactivity (IR) on the injection site. The [13 C]-octanoic acid breath test showed a delayed gastric emptying 4 wk after the 6-OHDA treatment. In control rats, microinjection of the indirect sympathomimetic, tyramine, in the dorsal vagal complex (DVC) decreased gastric tone and motility; this inhibition was prevented by the fourth ventricular application of either a combination of ␣1-and ␣2-or a combination of D1 and D2 receptor antagonists. Conversely, in 6-OHDA-treated rats, whereas DVC microinjection of tyramine had reduced effects on gastric tone or motility, DVC microinjection of thyrotropin-releasing hormone induced a similar increase in motility as in control rats. In 6-OHDA-treated rats, there was a decreased expression of choline acetyl transferase (ChAT)-IR and neuronal nitric oxide synthase (NOS)-IR in DVC neurons but an increase in dopamine-␤-hydroxylase-IR in the A2 area. Within the myenteric plexus of the esophagus, stomach, and duodenum, there were no changes in the total number of neurons; however, the percentage of NOS-IR neurons increased, whereas that of ChAT-IR decreased. Our data suggest that the delayed gastric emptying in a 6-OHDA rat model of PD may be caused by neurochemical and neurophysiological alterations in the brain-gut axis.brainstem; gastric motility; immunohistochemistry; Parkinson's disease IDIOPATHIC PARKINSON'S DISEASE (PD) is generally considered a movement disorder characterized by bradykinesia, rigidity, tremor, and gait/postural disorders related to the severe degeneration of the dopaminergic neurons in the substantia nigra pars compacta (SNpc) of the basal ganglia. Although the movement disorder has dominated the attention of clinicians and researchers, it is becoming increasingly recognized that PD also involves a prominent nonmotor pathology. In fact, patients with PD experience a remarkably broad spectrum of prodromic nonmotor symptoms that include sleep disorders, orthostatic hypotension, and gastrointestinal (GI) dysfunctions, all of which add significantly to the overall disability caused by PD (9,22,26,33,38,42).GI symptoms, such as dysphagia, nausea, delayed gastric emptying and dysmotility, and constipation, often precede ...

Enteric Dysfunctions in Experimental Parkinsons Disease: Alterations of Excitatory Cholinergic Neurotransmission Regulating Colonic Motility in Rats

“…In these experiments, colonic tissues from 6-OHDA rats displayed a significant decrease in immunopositivity for ChAT, whereas the overall density of HuC/D1 myenteric neurons did not vary, suggesting that nigrostriatal denervation leads to a reduced expression of ChAT in myenteric cholinergic neurons, likely resulting in an impairment of colonic cholinergic neurotransmission. Of note, Toti and Travagli (2014) recently described a reduced density of ChAT1 myenteric neurons in the upper GI tract, without a concomitant variation of total neuronal density in 6-OHDA rats. In line with this picture, evidence of unchanged overall density of myenteric neurons was previously obtained in patients with PD, suggesting that PD-related GI dysmotility is not associated with a loss of neurons in the myenteric plexus but rather with alterations in the chemical coding of specific enteric neurons .…”

“…In particular, there is evidence that the vagus nerve exerts tonic anti-inflammatory actions and contributes to the maintenance of intestinal homeostasis (Matteoli and Boeckxstaens, 2013), whereas vagotomy confers an increased susceptibility to the development of inflammatory bowel diseases (Ghia et al, 2006). In addition, Toti and Travagli (2014) recently found a reduced expression of ChAT in the DMV of rats with 6-OHDA-induced nigrostriatal denervation. Based on this knowledge, it is conceivable that 6-OHDA-induced nigrostriatal denervation might impair the DMV-vagus nerve anti-inflammatory pathway, and that this alteration might result in a condition of mild chronic bowel inflammation, leading to persistent dysfunctions in the enteric neuromuscular compartment.…”

A Nigro−Vagal Pathway Controls Gastric Motility and Is Affected in a Rat Model of Parkinsonism

“…After 7 days of recovery, rats were anaesthetized, euthanized with a bilateral pneumothorax, perfused-fixed, and the midbrain at the level of the SNpc and medulla were processed for immunohistochemistry 16 (see below).…”

“…At the conclusion of the experiments, rats were euthanized, perfused-fixed, and brain and gastric tissues were harvested for immunohistochemistry and localization of microinjection sites 16 .…”

“…The detailed methods were described previously 16-18 . Primary antibodies were i) rabbit-α -choline acetyltransferase (ChAT; Chemicon, Temecula, CA; 1:5000); ii) mouse-α-tyrosine hydroxylase (TH; Chemicon; 1:10000); iii) rabbit-α-cFOS (Santa Cruz Technologies, Dallas, TX; 1:1000; in these studies, rats were fixed 90min after NMDA microinjection in SNpc); iv) mouse-α-dopamine-1 receptors (Sigma, St. Louis, MO; 1:2500); v) goat-α-CTB (List Biological Labs, Campbell, CA; 1:100000); vi) rabbit-α-PGP 9.5 (Millipore, Billerica, MA; 1:500); vii) mouse-α- Ser 129 α-synuclein (Abcam, Cambridge, UK; 1:1000).…”