How does the intravenous administration of cholecystokinin provoke panic attacks? Background

I recently read a paper (The James-Lange theory of emotions: a critical examination and an alternative theory), in which the James-Lange Theory was challenged by Walter Bradford Cannon. 

Hence it was stated that:


  {Emotional responses can be distinguished by on the basis of autonomic activity., emotions were less intense when the brain was disconnected from the viscera} ... Some artificial manipulations of organ activity can induce emotions such as intravenous administration of of cholecystokinin (a gastric peptide) which can provoke panic attacks.


Question

What is the physiological process of intravenously inducing an emotion?
Emotions are often linked to chemical activity in the brain. Neurotransmitters such as serotonin , dopamine, norepinephrine etc are linked to inducing emotional states, therefore if you can take a drug which will increase the amount of a transmitter then you will respond accordingly e.g. MDMA > serotonin > feeling of escstacy/happiness (Meyer &amp; Quenzer, 2013).

In the case of Cholecystokinin (CCK), Singh et al found evidence suggesting that activation of the brain CCK-B receptor induces anxiety and that selective antagonists of this receptor represent a separate class of anxiolytic (relaxing) agents. 

Simply:


Inject drug  
drug reaches blood brain barrier  
drug crosses or is turned into drug that can cross (e.g. codiene > morphine) 
drug turns into neurotransmitter/ or precursor to (e.g. 5HTP > serotonin) 
binds to/ activates receptor this activation causes an emotional/physical
response


This process varies depending on the drug but that is loosely it as I understand it. Much of this taken from the Meyers textbook, which I read a long time ago so feel free to correct me. 

Singh, L., Lewis, A. S., Field, M. J., Hughes, J., &amp; Woodruff, G. N. (1991). Evidence for an involvement of the brain cholecystokinin B receptor in anxiety. Proceedings of the National Academy of Sciences, 88(4), 1130-1133.

Meyer, J. S., &amp; Quenzer, L. F. (2013). Psychopharmacology: Drugs, the brain, and behavior.