Trigeminal autonomic cephalalgias (TACs) comprise cluster headaches and are characterized by unilateral neuralgiform headache attacks associated with autonomic responses and somatic responses. An animal model for evaluating the anatomical basis of the TAC-like response is not currently available. Twenty-five rats weighing 550-650 g were anaesthetized with urethane. The TAC-like response was produced either by subcutaneous injection of formalin into the unilateral facial cheek or by electrical stimulation of the unilateral intact trigeminal nerve. The induced TAC-like response, which included ipsilateral common carotid arterial flow (iCCAF) and other autonomic responses, was studied in intact nerves or after cutting either the ipsilateral trigeminal nerve or the ipsilateral facial nerve. The formalin injections produced concentration-dependent iCCAF increases accompanied by ipsilateral autonomic responses of rhinitis-like nasal congestion, nasal mucus, meiosis, lacrimation, red eye, and eyelid oedema. The formalin (5% or 10%, 0.5 cc)-induced responses were nearly abolished by sectioning of either the facial or trigeminal nerve. The electrical stimulation (15 V, 60 Hz, and 0.4 ms) of the intact trigeminal nerve or its ophthalmo-maxillary branch also produced stimulation strength-dependent iCCAF increases as well as autonomic responses; however, the electrical stimulation-induced iCCAF increases and other autonomic responses could still be induced by electrical stimulation of the central but not the peripheral end of the ophthalmo-maxillary branch (n = 8) or the trigeminal nerve (n = 2). Thus, an animal model for inducing the TAC-like response by subcutaneous formalin injection into the rat facial cheek was established. The TAC-like response could be sequentially mediated via the afferent trigeminal nerve, trigeminal nucleus, dorsal facial nucleus, and efferent facial nerve.