Allopregnanolone: The missing link to explain the effects of stress on tic exacerbation?

Co-Occurring Anxiety in Youth with Tic Disorders: A Review

Objective: To review the current state of the literature regarding anxiety symptoms and anxiety disorders in chronic tic disorder (CTD). Results: We conducted a literature search on anxiety and tic disorders. Anxiety symptoms and anxiety disorders are common in youth with CTD, with ∼30%-50% of youth with CTD having at least one co-occurring anxiety disorder. Tics often improve by young adulthood but anxiety symptoms tend to persist, or worsen, over time. Anxiety and tics are closely related, but the exact nature of their relationship is poorly understood. We discuss some potential ways in which anxiety and tics are linked with an emphasis on the underlying brain circuitry involved. The relationship between anxiety and tics may be related to the premonitory urge. In addition, stress hormones may link anxiety and tics. Individuals with CTD have greater activation of their hypothalamic-pituitary-adrenal system in response to acute stress. We also review the impact of anxiety on youth with CTD and approaches to management of anxiety in youth. Conclusions: Anxiety is common in youth with CTD, is associated with more severe CTD, and can adversely affect a child's function. Thus, it is important to identify anxiety disorders in CTD and manage them appropriately.

Prefrontal allopregnanolone mediates the adverse effects of acute stress in a mouse model of tic pathophysiology

Ample evidence suggests that acute stress can worsen symptom severity in Tourette syndrome (TS); however, the neurobiological underpinnings of this phenomenon remain poorly understood. We previously showed that acute stress exacerbates tic-like and other TS-associated responses via the neurosteroid allopregnanolone (AP) in an animal model of repetitive behavioral pathology. To verify the relevance of this mechanism to tic pathophysiology, here we tested the effects of AP in a mouse model recapitulating the partial depletion of dorsolateral cholinergic interneurons (CINs) seen in post-mortem studies of TS. Mice underwent targeted depletion of striatal CINs during adolescence and were tested in young adulthood. Compared with controls, partially CIN-depleted male mice exhibited several TS-relevant abnormalities, including deficient prepulse inhibition (PPI) and increased grooming stereotypies after a 30-min session of spatial confinement - a mild acute stressor that increases AP levels in the prefrontal cortex (PFC). These effects were not seen in females. Systemic and intra-PFC AP administration dose-dependently worsened grooming stereotypies and PPI deficits in partially CIN-depleted males. Conversely, both AP synthesis inhibition and pharmacological antagonism reduced the effects of stress. These results further suggest that AP in the PFC mediates the adverse effects of stress on the severity of tics and other TS-related manifestations. Future studies will be necessary to confirm these mechanisms in patients and define the circuitry responsible for the effects of AP on tics.

Prefrontal allopregnanolone synergizes with D1 receptor activation to disrupt sensorimotor gating in male Sprague-Dawley rats

RATIONALE

The prepulse inhibition (PPI) of the startle reflex is the best-established index of sensorimotor gating. We documented that the neurosteroid allopregnanolone (AP) is necessary to reduce PPI in response to D₁ dopamine receptor agonists. Since Sprague-Dawley (SD) rats are poorly sensitive to the PPI-disrupting effects of these drugs, we hypothesized that AP might increase this susceptibility.

OBJECTIVES

We tested whether AP is sufficient to increase the vulnerability of SD rats to PPI deficits in response to the D₁ receptor full agonist SKF82958.

METHODS

SD rats were tested for PPI after treatment with SKF82958 (0.05-0.3 mg/kg, SC) in combination with either intraperitoneal (1-10 mg/kg) or intracerebral (0.5 μg/μl/side) AP administration into the medial prefrontal cortex (mPFC) or nucleus accumbens shell. To rule out potential confounds, we measured whether SKF82958 affected the endogenous mPFC levels of AP.

RESULTS

SD rats exhibited marked PPI deficits in response to the combination of systemic and intra-mPFC AP with SKF82958 but not with the D₂ receptor agonist quinpirole (0.3-0.6 mg/kg, SC). SKF82958 did not elevate mPFC levels of AP but enhanced the content of its precursor progesterone. The PPI deficits caused by SKF82958 in combination with AP were opposed by the AP antagonist isoallopregnanolone (10 mg/kg, IP) and the glutamate NMDA receptor positive modulator CIQ (5 mg/kg, IP).

CONCLUSION

These results suggest that AP enables the detrimental effects of D₁ receptor activation on sensorimotor gating. AP antagonism or glutamatergic modulation counters these effects and may have therapeutic potential for neuropsychiatric disorders characterized by gating deficits.

Altered visual cortex excitability in premenstrual dysphoric disorder: Evidence from magnetoencephalographic gamma oscillations and perceptual suppression

Premenstrual dysphoric disorder (PMDD) is a psychiatric condition characterized by extreme mood shifts during the luteal phase of the menstrual cycle (MC) due to abnormal sensitivity to neurosteroids and unbalanced neural excitation/inhibition (E/I) ratio. We hypothesized that in women with PMDD in the luteal phase, these factors would alter the frequency of magnetoencephalographic visual gamma oscillations, affect modulation of their power by excitatory drive, and decrease perceptual spatial suppression. Women with PMDD and control women were examined twice-during the follicular and luteal phases of their MC. We recorded visual gamma response (GR) while modulating the excitatory drive by increasing the drift rate of the high-contrast grating (static, 'slow', 'medium', and 'fast'). Contrary to our expectations, GR frequency was not affected in women with PMDD in either phase of the MC. GR power suppression, which is normally associated with a switch from the 'optimal' for GR slow drift rate to the medium drift rate, was reduced in women with PMDD and was the only GR parameter that distinguished them from control participants specifically in the luteal phase and predicted severity of their premenstrual symptoms. Over and above the atypical luteal GR suppression, in both phases of the MC women with PMDD had abnormally strong GR facilitation caused by a switch from the 'suboptimal' static to the 'optimal' slow drift rate. Perceptual spatial suppression did not differ between the groups but decreased from the follicular to the luteal phase only in PMDD women. The atypical modulation of GR power suggests that neuronal excitability in the visual cortex is constitutively elevated in PMDD and that this E/I imbalance is further exacerbated during the luteal phase. However, the unaltered GR frequency does not support the hypothesis of inhibitory neuron dysfunction in PMDD.